Side project - restoration work on Millivac MV-864A meter, part 2

METER DOES NOT MECHANICALLY RESTORE ALL THE WAY TO ZERO POINT

The meter on the face has a screw that changes a coil spring tension to make the pointer align exactly with the left side (zero) position of the scale. Moving the screw will move the pointer further away or closer but it never gets all the way to the zero line. Not sure what I will be able to do about this.

DECIDED TO CHECK POWER SUPPLY VOLTAGES AND OTHER CHECKS OF THE CIRCUITS

I opened the meter, with the expensive manual I purchased, looking for the test points listed for the +8.5, -6 and other voltages. The first thing I noticed is that the board shown in the manual does not look like my board. The one in my meter is larger and includes the resistor networks for the range switch. 

More importantly, it has no test points labeled TP1, TP2 and TP3. It does have points such as TP63, TP61 and TP62, but they are tied together or otherwise don't make sense as the place to check the supply voltages. 

The schematic shows five transistors, five diodes and a bunch of passive components for the power supply, but mine had only two transistor looking objects. The schematic has silicon transistor numbers on it, but my board has an obsolete germanium MHT3030 power transistor made by GPD Optoelectronics and a GE RA1 three lead component. 

I was able to track down an old GE manual and found the RA1 as a reference controller for power supplies, consisting of a germanium transistor and a zener diode encapsulated in a single TO-5 style can. The GE manual showed me an example circuit which matches decently with the connections I can see on my meter's board. 

I am reverse engineering the power supply part of the PCB in my meter - components that start with a 6 such as R601 or C602. The power transformer and the primary side circuit match well, but it diverges on the output side. The transformer has a long winding with three taps between the two ends. The center tap and the two outer connections are fed through a pair of diodes (half wave rectifier) in both the schematic and in my board. If you number the secondary wires as 7, 5, 8, 6, 9 then the center tap is 8 and the ends are 7 and 9. 

On the schematic, 5 and 6 are unconnected. The pilot light is powered from a resistor off the output of the two diodes. Yet, on my meter, windings 5 and 6 are connected to the pilot light, driving it with AC. 

I am carefully reverse engineering the power supply as it exists on my meter, drawing it out and noting parts values. I will then check whether it is working as intended and make adjustments if necessary. That will happen in a later workshop session. 

I paid a relatively high price for the manual from the manufacturer, who used my serial number but didn't have a version of the manual old enough. The sent me the oldest version in their files, which as I mentioned was in the silicon semiconductor era while mine is an old design using germanium devices. I suspect I will find many differences in the rest of the manual and schematic as I work on this project. 

More Bench Testing of the 1130 MRAM memory board

FLAKY BEHAVIOR OF DIRECT PORT MAPPING OBSERVED

I ran the program to load the memory and happened to put a scope probe on the Storage Write signal which I should be toggling on for each of the memory locations, but saw the signal stuck steadily at high. In some other cases I saw results that didn't match what I expected from the program to read memory.

I switched back to digitalWrite from the direct port access just in case there was something going on that I didn't understand with port access on the Due, which has an ARM chip rather than the usual Arduino processor type. 

 However, in retrospect this is due to the weirdness that occurs when the laptop is plugged into the wall using its power brick. Running just on batteries should eliminate these gremlins. 

NEW PROGRAMS LOADED INTO ARDUINO AND TESTING RESUMED

I ran the loader program that wrote the values 1, 2, 4, 8, 16 . . . 8192 into locations 0, 1, 2, 4, 8, 16 . . . 4096. These locations and values were chosen to have a unique wire I could monitor for each choice. This simplified triggering and monitoring on the oscilloscope.

I saw the B register inputs set low for the desired address and the board was generating the inverted write control signal that causes the MRAM chip to write the data into the selected memory location. The control signal is applied for a bit under 100 nanoseconds and the B register data is gated through to the memory chip at the same time. 

However, when I then ran the reading program (below), all outputs were 0. I could clearly see the address and the B register inputs were correct and all the control logic signals on my board worked properly for the writes. The address and all control logic signals were correct on my board for the read, yet the data was not the 1 value I expected. 

My XOR logic is producing a 1 for each of the two check bits and those pulses are emitted correctly during the reads. Earlier I had seen outputs that were 1 but my guess is that the strange power injection when my laptop is on AC power, through the Arduino, has damaged one or more chips on my board. 

Possible bad chips are the MRAM memory itself, the buffer chips feeding it the B register data, or some of the open collector NAND gates that pass along the pulse for any 1 bit read. Once I pin down the failure further I can replace parts and resume testing. 

NEXT SESSION PLAN

I will tack wires on the data bit 15 pin of the MRAM chip and on the input to the buffer that feeds the B register values to the chip. Using the scope, I will be able to verify that the B register value reaches the buffer and is passed through at the proper time to the MRAM pin. I can then look at the MRAM chip pin when doing a read to see if the 1 bit is making it back out. I will also be able to see if there is a 1 coming out of MRAM on a read but no pulse out of the NAND gates. 

Bench testing strange power supply behavior testing MRAM board - followup

FROM TIME TO TIME, BENCH SUPPLY SHOWED ZERO POWER DRAW

I was puzzled why this occurred yet 3.3V appeared on the output line going to my PCB. I originally ascribed this to buffer capacitors not needing energy pumped into them for a period, but this didn't really satisfy me. 

DISCOVERED THIS IS A CONSEQUENCE OF LAPTOP POWER BRICK CONNECTION

The test setup for the 1130 MRAM core memory replacement board used an Arduino Due to drive signals onto my PCB, a bench supply to deliver the +12V that will eventually come from the 1130 computer, a prototyping tool that provides the 3.3V pullup for the open collector sense output lines of my board, and an oscilloscope to capture the behavior of the board under test. 

The Arduino gets its power from the USB cable connected to my laptop. The ground of the Arduino, bench power supply, prototyping tool, oscilloscope and my board are all tied together. The odd behavior occurs when I have my laptop plugged into its charging brick - somehow this is causing difficulties but if I just run the laptop on batteries all is well. The brick must be driving energy into the test system somehow. The laptop is a Lenovo L340. 

Continued testing of the 1130 MRAM Core Memory Replacement board

SWAPPED IN THE HC CHIP VERSION FOR 3.3V SUPPLY

I had installed 7400 series chips (and other types) on the board that were able to work on a 3.3V power supply, but a recent switch from an AND to a NAND gate, open collector, I put in 74LS03 which require a minimum of 4.75 VCC. The 74HC03 parts arrived last night and were installed on the board. 

TESTING ON THE BENCH

I am working to rigorously test the PCB while on the bench before I install it on the IBM 1130 system. I wanted to write to different memory addresses using unique data values, then test by reading the locations and comparing the returned values. 

I whipped up some code on an Arduino Due (because it uses 3.3V logic levels), expanding on my previous code that generated the correct timing of Storage Read and Storage Write signals that would come from the IBM 1130. These alternated for 1.8 microseconds duration. I stored fourteen addresses and corresponding data values in the program then stepped through the list cyclically. At the start of a Storage Read it sets the memory address (and data value for the upcoming write). The Sense pulses are generated during the Storage Read and then the location is updated during the Storage Write. 

I used direct port mapping to write the pins since the DigitalWrite function is relatively slow. The Due requires that a 1 be written in one control register to turn on a pin, but it doesn't turn off it 0 is written there. Instead, a 1 has to be written in a different control register that clears pins. 

After the first pass, the memory would have had all locations set up with the prepared values from the program. I would then set the scope to trigger on Storage Read rising edge or an address bit rising edge and monitor three output lines from the board at a time. Due to limited pins on the Arduino, I couldn't simultaneously produce the 16 B register data values, the 13 SAR address values and capture the 16 Sense pulses to verify. 

With just 3 pins that I can monitor at a time on the scope, I had to be clever to test the correct data returned from each location. These are open collector inverted outputs, thus a 1 bit pulls its pin to ground else it is pulled up to 3.3V using a resistor.

The addresses I chose were 0, 1, 2, 4, 8, 16, 32, 64. 128. 256, 512, 1024, 2048 and 4096. I can uniquely trigger on those addresses except for address 0. The values written were 1 through 14 decimal in sequence. 

I had previously validated that all 16 sense pulses are generated when the corresponding bit was written in memory, also that all 16 of the data value (B reg) bits were stored in the memory words. This is just a test to be certain that we are addressing memory correctly. Any result of 0 detects an addressing or write failure. 

When I tried to observe the outputs from the Arduino I found that it just could not keep up with the 1.8 microsecond durations of the memory cycle. To get reliable results, I had to slow it down to 1.8 milliseconds for read and 1.8 milliseconds for write. That won't stop my memory board from working, since my logic triggers on the edge of the read or write signal and its not sensitive to its duration. 

The connections using jumper wires are a bit fragile, thus I had to deal with some erratic results. More frustratingly, I would sometimes turn on the +12V bench supply and see zero current being drawn. The wire connection on my PCB showed 3.3V which is the correct output of the regulator, so I didn't understand why this was happening. 

UNDERSTANDING THE WEIRD RESULTS

The power confusion is due to the ability of the voltage regulator to buffer quite a bit of energy, when combined with the very low draw of my board, so that it can sit drawing zero power from the bench supply for long periods. 

I then realized that the slow speed I set up for alternating Storage Read and Storage Write cycles didn't completely solve the glacial relative speed of the Arduino compared to my board. I saw that the delay from when I set Storage Read high until the main loop of the software set the Storage Address Register and B Register outputs to the board was approximately 6 microseconds. I was already using direct port mapping for speed but the problem is that the read is accomplished rapidly and the output is provided from my board in about 800 nanoseconds (0.8 microseconds) thus the data being read does not have the proper address yet. 

The residual address from the prior pass of the Arduino code is what the MRAM is reading, not the one I intended. I checked a few cases and felt comfortable that this is why I see the wrong bit being output for a given address.

WILL REWRITE THE ARDUINO DRIVING PROGRAM

I cannot use the timer based 1.8 microsecond or even the drastically slowed 1.8 millisecond control signals because the Arduino can't set up all my outputs in time for the very fast board circuitry. Instead, I will use the Arduino at its native speed to set up the SAR and B values, then toggle the Storage Read and Storage Write signals from the code. 

Specifically, I will split the program into one that only does Storage Reads in order to observe with the oscilloscope as above. The other version of the program will execute one pass writing the intended values into memory. 

Restoration of top cover glass for IBM 1132 printer

GLASS BROKE ON TOP COVER

The cover of the 1132 printer has a glass window to allow the operator to watch what is being printed while lowering the noise due to the cover being closed. Sometime in the past this printer had its glass cover broken - bits of glass were inside the machine although most had been cleaned up before I received the machine for renovation. 

The glass had rubber channels around all four edges. These fit under metal channels that hold the rubber and glass up against the underside of the printer cover. 

All the parts to hold the sheet of glass in place were present - minus the nuts - so all I needed to do was buy a replacement glass or acrylic sheet to the correct size.

BUYING REPLACEMENT ACRYLIC

Ace Hardware in my area has a service to cut acrylic sheets to size, which is perfect for a replacement. They can also cut glass if I decide to go with a glass sheet instead. I carefully measured the size I needed and then went to the hardware store to get the new window cut. 

The rubber channels from IBM are so degraded that they don't work well. I believe I will need to buy some weatherstrips and press them into service. 

Too, one of the edges is rusted out (see below). I fit the acrylic I had cut onto the printer, but have left the peel off plastic cover to minimize scratches until the printer arrives back at its home in New Jersey.

DEALING WITH SEVERE RUSTING ON RECESS IN THE COVER

The glass plate is slanted with the front lower and the back higher so the operator looking through the top gets a good view of the printed page yet the cover clears the tall forms tractor on the back of the carriage. This forms a recess at the front where rainwater collected and sat for long periods of time, judging by the rusting away of the sheet metal rising vertically from the glass to the top of the cover at that recess. The paint is peeling away, creating a mottled appearance of rust and thick peeling paint. 

I plan to remove the paint from the vertical sheet, sand the surface a bit, use rust converter to seal the surface, and then spray paint as close to a color match as I could. The same spray paint will be used to touch up the rotary mode switch on the IBM 1130 which had some rust spots and peeling paint. 

Reassembly of the 1132 printer - part 9

REED RELAY REPLACEMENT PCB ASSEMBLED AND ATTACHED

A complex reed relay (RR1) was discovered to have an open coil. This relay has four reed switches - two are normally closed and two are normally open. Three of the four switches are used by the PCB that contained this relay. It had a 48V coil. 

The RR1 relay activates when the printer controller logic in the 1130 has activated the Carriage Magnet to move the paper down one line or to skip until a hole is detected in some channel of the carriage control tape. 

Three relays RR1, RR2 and RR3 are used in order to have the Silicon Controlled Rectifiers energized from the time the Carriage Magnet is activated until the printer carriage reaches the next line position where the Carriage CB switch closes.  

I was not able to find a similar reed relay but worked out a solution using a pair of SPDT reed relays to substitute for the three reed switches that were used in RR1. The relays were not 48V, thus I also had to drop the voltage to the 5-6V range of the parts I bought. A small PCB I designed mounted the two reed relays and the dropping resistor. 

I installed the two replacement reed relays, which were in 8 DIP form, plus a 2W resistor onto my new PCB. I added wires between this small PCB and the main IBM PCB which had contained the failed RR1 relay. 

CARRIAGE CONTROL TAPE PCB REINSTALLED

The IBM PCB mounts on the side of the frame at the right rear of the machine, with three connectors that plug into it from two sides. With that in place, I mounted the small new PCB with my relay substitute just above it. 

FORMS TRACTOR AND PAPER FEED GUIDES INSTALLED

The printer uses continuous forms with pin feed holes on the two edges of the paper. A tractor mechanism holds the paper with pins through the feed holes and advances it when the platen turns. This was inserted on top of the carriage mechanism.

A guide attaches to the top rear of the carriage to guide the new paper up into the forms tractor and to guide the printed pages as they come out of the machine. Often the operator would have a box of blank forms up against the rear of the printer with the paper fed up through the tractor and then an empty box behind the blank paper box to catch the output as it comes down from the paper guide. 

Dealing with the broken clutch fork on the 1132 printer carriage mechanism

IDENTIFIED BROKEN PART IN CARRIAGE

The knob which switches the platen in and out of engagement with the gear box is shown in the diagram below from the parts catalog, with the parts circled in green. The knob rotates and a pin on the inside turns with the shaft. That pin fits in the notch in the metal fork piece on the top of the assembly to the right.

The next diagram is an exploded view where you can see the piece that has one of its fork tines broken off. It is hooked onto the shaft with a tapered pin. 

With one of the tines of the fork broken, the pin on the back of the knob shaft can't move the fork back and forth, twisting the shaft to cause the platen clutch to engage or disengage. I believed I needed to restore the U shaped channel or add back the second tine so that the knob shaft can cause the fork's shaft to turn in both directions.

FINDING THAT SPRING IN CLUTCH OBVIATES NEED FOR THE SECOND TINE

While I was watching the motion of the knob and the fork, considering ways to replace the tine's function, I noticed that the platen clutch would be held out of engagement by the remaining tine when the knob was turned to Out but when the knob is turned to In, the clutch pulls the fork over to engage. 

That is, the tine doesn't need to move the fork since the spring force in the clutch assembly is trying to pull it to the engaged side at all times. It takes positive force to disengage, using the remaining tine, but when that force is removed the clutch snaps into operation. 

NO WORK NECESSARY, THE IN/OUT KNOB WORKS PROPERLY AS IT IS

I can cross this task off the restoration list since the printer works properly without having to address the broken tine of the fork. 

Side Project - Restoring an HP 4261A LCR (inductance, capacitance and resistance) meter

HP LCR METER

The 4261A meter measures the resistance, capacitance or inductance of components. It applies signals at 120Hz and 1KHz, treating the attached device as an series or parallel equivalent circuit. It measures resistances from 100mΩ to 10MΩ, capacitance from 10pF to 10mF, and inductances from 10 μH to 1000H. 

In addition it measures the dissipation (energy loss due to phase angle) for inductance and capacitance. The meter steps through ranges and in auto mode will even switch between series and parallel equivalent measurements for the device. 

QUICK INSPECTION

The device was a bit dirty but seemed in good shape otherwise. It had been powered on by the seller so I did the same and tried some measurements. The results were reasonable and the device appeared to be mostly working okay. 

I will perform all the tests and adjustments using the manual, after which I will determine whether there are any defects I have to find and fix. I ordered high precision capacitors, resistors and inductors for the testing. 

TESTING POWER SUPPLIES

The power supply was slightly off, but after adjustment all was correct with power. 

SELF TEST CHECKS

The device has two self tests that can be performed by sliding a switch on the inside to either test 1 or test 2 positions. I ran both tests. 

Test 1 will step the device through all its ranges, displaying a count of 1888 with proper decimal point positioning and a dissipation reading of 000. I saw a few ranges where it displayed 'out of range' instead of 1888, but the manual indicates that this is the expected result. 

Test 2 will display measured values of 1000 as it steps through all ranges, with some tests using shorted input terminals and others using open terminals. A few ranges were 'out of range' but that was also to be expected. 

I will run calibration and adjust this meter once my reference parts arrive, which will give me a very useful tool when I am repairing devices. 

Side project - repairing a Sony VP-5000 U-Matic video tape deck for the Space Force Museum

U-MATIC VIDEO MACHINES FOR PROFESSIONAL VIDEO WORK

The video recorder/playback universe spanned broadcast studio requirements with its 2" high speed tape down to home units such as VHS or Betamax with 1/2" wide tape. An intermediate level of quality (and expense) existed for professional but non-broadcast uses, such as the Sony U-Matic machines using 3/4" wide tape cassettes. 

EXAMINING THE MACHINE AND IDENTIFYING PARTS NEEDING REPLACEMENT

I opened this up and looked over the machine to see if there are any signs of damage or parts that definitely need replacement. I expect that the rubber parts are degraded. They didn't seem to be have hardened to develop cracks but I suspect their elasticity is lessened which would cause slippage for belts. 

EBAY KIT AVAILABLE FOR THE RUBBER BELTS AND TIRE

I found a kit with the rubber drive belts and the rubber tire for the main drive wheel which I purchased from eBay. This should give me replacements for all the worn parts, as these typically dry out on these machines (and on their Betamax smaller kin). The parts arrived and were ready for the restoration work. 

PURCHASE SERVICE MANUAL INCLUDING SCHEMATICS

Having the detailed schematics, adjustment procedures and other service information is essential to get a device like this operating properly. I received it and was ready to move forward with the restoration. 

CASSETTE LOADS BUT MACHINE GOES TO STANDBY, WON'T EJECT

Sliding the cassette into the front of the drive starts the load sequence, where it lowers the cassette into the machine, threads the tape around the head and should then be in stop mode waiting to play or perform other operations. Instead the deck enters Stand By mode which indicates some issue arose. Hitting Eject will not unload the tape, the machine remains in Stand By state. 

BELTS AND TIRE REPLACED, STILL GOES INTO STANDBY MODE

Once the new rubber was installed I tried again and did get the tape to load then let me start playback. However, attempting to return to Stop mode, rewind, fast forward or eject forced the machine into Stand By mode.

replaced main capstan motor

closing up the bottom side

Replaced belt that drives the threading motor and tire

Replaced cassette loading belt

DISCOVERED THE PINCH ROLLER ARM IS STICKING AS IT PIVOTS

There is an arm that moves the pinch roller on the tape to deliver controlled speed during playback, then moves out of the way for eject or fast tape movements. The arm stuck partway out, which the logic detected as a failure to complete its mechanical motion. There are many sensors in the deck to provide feedback to the logic state machines. 

I realized that it was just sticky old lubrication causing the problem. I partially disassembled it and dropped in some clock oil. The lever soon returned to free movement, so that the machine will now load, eject, play, rewind and all the other mechanical operations. 

NEXT UP - DISPLAYING IMAGE TO VERIFY THAT VIDEO AND AUDIO WORK

I will play the tape I brought with me from the museum and attempt to connect it to a monitor and audio system. The mechanisms might be moving tape just as intended but if the electronics can't extract the contents from the tapes it will still be broken. 

If it is working, I will make all the adjustments and lubricate it so that it is ready for use extracting content from the archives. 

Installation of new rubber drive belts for IBM 1132 printer

TWO DRIVE BELTS WERE IN BAD SHAPE

A pulley in the machine steps down the speed of the AC motor to produce 300 RPM at the print clutch cam shaft and 111.6 RPM at the print wheel.  The print wheel spins through the 48 characters that the printer can produce, thus it takes just over half a second to complete one rotation. 

Any print line that uses all 48 of the characters would need about 0.54 seconds to print on all the columns with all the characters. Spacing down one line in order to print the next line on the page takes approximately .2 seconds, allowing time for the print wheels of the last character being printed to finish movement and for the carriage to move down one line. 

This means the absolute maximum rate that lines with all 48 characters can be printed is about 1.36 lines per second, roughly 81 lines per minute. Lines with fewer characters can finish when the last character that exists on the line has been printed. For example, lines with only numbers could print around 110 lines per minute. A standard page at 6 lines per inch vertical pitch has 66 printable lines, thus the printer barely prints faster than 1 page per minute. 

There is a belt from the motor to the pulley, and a second belt that runs from a different circumferential ring to the gear train that links the print clutch cams and the print wheels. These had sat in a fixed position for decades, thus the rubber set into the shape and would thump for quite a while until (if) it relaxed to neutral shape. Worse, one of the two belts had a tear from the inside edge almost all the way to the outer edge, which would cause the belt to completely fail in a short time. 

NEW BELTS WERE PUT ON THE PULLEYS

I measured the belts, which where 1/2" width standard V belt shapes, and found new belts of the correct size which I could order. When they arrived, I installed them on the pulleys. A protective metal shield covers the belts and pulleys. Fitting that in place around the belts and pulleys was surprisingly difficult. It required a staged assembly - removing a top plate, leaving the center pulley too lose for proper belt tension, installing the metal cover, then reinstalling the top plate. After all that, the belt tension gets set with the belts mostly hidden under the cover!

ADJUSTING AND TIGHTENING CENTER PULLEY TO ATTAIN DESIRED TENSION

The nut on the back of the center pulley axle is accessible from behind the covered belts and pulley. A lug behind the nut allowed me to pull the pully axle to achieve a good tension in both belts. I tested by poking a finger through holes in the metal cover, tweaked the axle position, then tightened it up. 

Reassembly of the 1132 printer - part 8

TOP COVER REATTACHED

The top cover went on next, hinging at the rear and held open by a dashpot and lock plate. The dashpot moderates the rate that the cover closes. 

ORDERED NEW RUBBER DRIVE BELTS

The motor to pulley belt is a 34 1/2" x 1/2" V belt and the pulley to clutch pulley cam shaft belt is a 36" x 1/2" V belt. I ordered one of each from Amazon and had one of them when I returned from a week trip to Rhode Island; the other will arrive in a few days.9

DEALING WITH BROKEN GLASS ON TOP COVER

The printer had a glass window on the top cover, but it had been broken prior to my receiving the equipment. It won't be a complicated repair since it is a simple rectangle shape, I just need to measure, order and install a replacement. In the meantime I installed the top cover to complete the reassembly of the printer. 

GOT MY PCB TO REPLACE REED RELAY ON THE SIDE PCB

One of the three reed relays on the printed circuit board mounted on the left front of the printer frame had an open coil. I bought a pair of reed relays that will fit on a small daughter PCB I will mount above the IBM PCB to replace the functionality. The remainder of the IBM PCB works properly and just needs to be mounted and connectors attached once I finish up the daughter PCB connection to the IBM board. 

WAITING FOR REPLACEMENT RIBBON

This printer uses 3/4" wide black ribbon wound on open spools. Each end has a rivet that will trip a reverser so that when the end arrives as the machine winds in one direction, the reverser begins using the ribbon in the opposite direction. I have to buy an inked 3/4" ribbon, put on the rivets and attach it to the IBM spools. I found a supplier who provides as many yards of 3/4" ribbon as I wish. The original IBM ribbons are 18 yards long. 

AWAY FOR A WEEK

I am away for a week visiting my daughter, but that gives time for the drive belts and some other things to arrive for when I dive back in early next week. 

Reassembly of the 1132 printer - part 7

FINISHING THE PLATES AROUND THE PRINTER MECHANISM

After some cleaning to remove the surface dust, rust and rodent sludge, I began fitting the remaining plates onto the printer. These are mainly the left mid and front section, but there is also a metal shield around the rubber drive belts and pulleys. 

INSTALLING DOORS ON THE PRINTER

The six doors that fit around the printer pivot on hinges with pins that hold them in place. I put them all back but had to leave as I have other appointments this afternoon. 

Reassembly of the 1132 printer - part 6

REINSTALLING CARRIAGE ASSEMBLY

I brought the mechanism over from the workbench on my hydraulic lift cart so I didn't have to carry it myself due to its weight. I had a wood board placed over the frame onto which I placed the carriage.  I then slide the carriage and lowered it onto its mounts in the machine. 

Bar onto which the carriage installs

Carriage in place

front view of carriage in place

The board went away and I began reinstalling the metal plates that form a floor around the printer unit when viewed from the top of the printer. This involved temporarily lifting one end of the carriage to get two of the plates in place inside the frame. To lift the carriage, the shoulder bolt for the right side has to be removed to tilt the unit up. 

There is a catch-22 situation between the carriage, the metal plates and the shoulder bolt. The bolt unscrews on the same plane as the metal plates, thus one of them will prevent removing or reinserting the bolt. This is the right rear plate. 

The right front plate needs the carriage lifted to get the plate inside the frame for attachment. The left rear plate needs the carriage lifted to get that plate under the carriage assembly since the sheet is formed to fit around some brackets under the carriage. 

obstruction blocking left rear plate from sliding under carriage

Once the right front and left rear plates are attached and fastened down, the carriage is lowered and the shoulder bolt tightened. This has to occur with the right read plate out of the machine. That plate is slid in from the bottom and just makes it past the frame and other obstructions, so that it can also be fastened down. 

The  cable plug was reinserted into the receptacle on the rear of the carriage and its cable straps bolted down on the frame. The ground strap was reconnected from the carriage to the frame. 

INSTALLING PRINT WHEEL ASSEMBLY

The Print Wheel assembly was lowered into place next. Rusty frame and very tight machined fit, so it didn't just slide into place. It did take some judicious tapping with a hammer to move it down to the position where its bolts could be reattached. 

The home-made alignment tool (cut up aluminum ruler) held the wheels in the gap between the R and E characters. I had set the timing disk wheel so that the hole pattern for the numeral 9 was in front of the photocells - this is the position that synchronizes with the wheels when they are held by the alignment tool. I carefully rocked the timing wheel to get the print wheels to mesh with the driving gear at this position. 

Removing the home-made tool was the last step before I covered the wheel and print clutch mechanisms with a plate that hides it from the operator. 

The right side and top plates are all in place, but I am not finished covering the left side. The plates for that were still a bit dirty, so I moved them to the bench where I will clean them off before attaching them in the next work session. 

HAND ROTATION OF PRINT MECHANISM TO ENSURE NO OBSTRUCTIONS EXIST

As my last sanity check, I spun the print mechanism by hand to ensure that no columns were being triggered inadvertently. All print cams did remain at the rest position. Most of the remaining work will be cosmetic, things like the remaining covers, the top and all the doors. 

REATTACHING THE BACK COVER WITH USAGE METER

I bolted the back high cover onto the machine - it had to be removed to use the board to slide the carriage in and out. The printer is looking more and more like the complete product. 

Reassembly of the 1132 printer - part 5

LOOSENED AND ADJUSTED THE RESTORE AND DETENT BARS

I was able to achieve low resistance when I hand turned the print mechanism with all the detents holding their cams in the stopped position and the restore levers attempting to reset the Print Clutch Latch to stop any cams that were turning. 

LATCHING AND RELEASING THE PRINT CAMS

The normal (rest) position of the Knockoff Armature Lever, which has a notch on the end, leaves the high point on one side of the notch underneath the Print Clutch Latch lever. The end of the Print Clutch Lever will bump into the Print Clutch Dog, stretching the spring and pivoting the dog so that its tooth is lifted out of the flutes of the Print Clutch Shaft.

When a magnet causes the Knockoff Armature Lever to pivot, the Print Clutch Latch tip is pulled into the lever notch du to the springs in the latch mechanism. As shown below, the Print Clutch Latch lever pulls off the end of the Print Clutch Dog, whose spring pivots it so the tooth slides into the next flute in the rotating Print Clutch Shaft turning inside the cam. 

Putting this all together, the diagram below shows how all these parts cause the clutch to stop the Print Cam from rotating when the Knockoff Armature Lever is at rest. When the print magnet pulls on the linkage, the Knockoff Armature Lever causes the clutch to be released and the Print Cam begins rotating with the Print Shaft. 

Since the print magnet will disengage quickly, the spring in the Knockoff Armature Lever is ready to pivot it back to its rest position. As soon as the Print Cam actuates the Print Clutch Restore Lever, the Print Clutch Latch is pushed back up and the Knockoff Armature Lever snaps back to its rest position. 

The Print Latch Lever is up in the path of the Print Clutch Dog, allowing it to push the tooth out of the flutes and stop the cam at the end of one rotation. Meanwhile, before the cam comes to a rest, the high point of the cam pushed against the print wheel hanger and caused it to rotate to contact with the ribbon, paper and platen to print a character. 

HAND TESTING OF THE PRINT MECHANISM

With the Print Restore Levers and the Print Clutch Detent levers in place, with the Print Clutch disks oriented to their rest positions, but the Knockoff Armature Levers not yet installed, I tested the mechanism by rotating it by hand.

Without the magnet assembly and its Knockoff Armature Levers in place, all the clutches are triggered by the Print Clutch Latches. The Print Clutch Latches on all of the columns will be pulled away from the Print Clutch Dog. The cams should all turn with the Print Clutch Shaft as a result. 

About one quarter of the way around one rotation, the Print Clutch Restore levers will try to push the Print Clutch Latch back onto the Print Clutch Dog. Without the Armature Knockoff Lever in place, the latch will not activate and the dog tooth remains engaged; it would continue to turn after the first rotation. The only way to stop the rotation is to have the Print Clutch Latch hold the Print Clutch Dog out of the way, which requires the latch to be pushed against its spring either by hand or by the Armature Knockoff Lever. 

When the disks reach about three quarters of a rotation, the high lobe pushes against the Print Wheel Hanger which would complete the printing action. I haven't installed the Print Wheel assembly with the hangers yet so the lobe isn't actually striking anything. 

As mentioned above, all the clutches will trip again at the end of a rotation. However, I can hold up a few Print Clutch Latch levers by hand while rotating, which should cause the Print Clutch disks for those columns to stop turning when the restore lever does it thing. The Print Clutch Detent Lever should keep those cams resting quietly at their idle position. 

The hand stop test worked, when the Print Clutch Latch levers are held in their idle position the associated print cams stop at the detent. 

REINSTALL THE MAGNET UNIT WITH THE KNOCKOFF ARMATURE LEVERS

The magnet unit has the Knockoff Armature Levers which hold the Print Clutch Latch levers against their springs so the latch keeps the Print Clutch Dog from engaging its tooth into the Print Clutch Shaft flutes. The Print Clutch Latch sits on a high point on the Knockoff Armature Lever to accomplish this. 

I slid the magnet unit into the frame and bolted it down. 

HAND CYCLING TO VERIFY ALL CAMS STOP IN THEIR IDLE POSITION

Turning the print mechanism by hand should cause all Print Restore Levers to relatch the clutches on all 120 columns, thus the cams should all stop with the Print Clutch Detent levers in the notches of the cam. Pulling on a link for a column while turning the mechanism should release that one column and cause its print cam to make a single revolution before stopping in the rest position.

That worked perfectly and when I flicked one of the linkage levers in the magnet unit, its print cam performs one rotation. At this point I added the print magnet plate to the magnet unit and confirmed that the idle condition still keeps all the print clutch cams at their stopped detent position.  

Magnet unit and print magnet plate installed

Reassembly of the 1132 printer - part 4

INSTALLING RESTORE LEVERS

The Print Clutch Restore Levers were installed as they will push the Print Clutch Latch Levers so that the Print Clutch Dog is held by the end of the latch lever. They are a more complex set of bars that bolt on midway on the frame at the front side. 

The high point of a lobe on the Print Cam pushes the restore lever, which pushes the Print Clutch Latch up out of a notch on the Knockoff Armature Lever and allows the lever to pivot so the latch will sit on the high part of the Knockoff Armature Lever. 

I was able to install the assembly but the Print Clutch Cams won't rotate past the restore levers. These bars have adjustments to be certain that they lift the Print Clutch Latch out of the Knockoff Armature Lever notch sufficiently but without the restore lever bottoming out on the guide bar onto which they pivot. 

Restore lever assembly outlined in yellow

I will have to loosen this and tweak its position until I can hand rotate the mechanism again. 

REMAINING PARTS TO INSTALL

The carriage must be installed back on the printer, now that it is restored. 

When that is in place, I can drop the Print Wheel assembly into place.

The magnet assembly goes on the front of the print mechanism frame after that. When it is installed, the plate with the 120 magnets gets dropped on and that completes the main part of the printer reinstallation. 

Restoration of the 1132 printer carriage mechanism - part 2

DETENTS WORKING WELL

As the clutch solenoid plate is pulled (as if the magnets were energized), the slow or high speed clutch activates and turns the platen. The detent pops in so that it stops crisply at the nearest print line position. The CB switch plunger pops in and out correctly. No work needed on these functions. 

PLATEN DISENGAGE/ENGAGE LEVER WORKING

The front lever that engages or disengages the platen from the gears was frozen solidly in one position. I got into the mechanism, oiled it and now the lever does what it should. The operator can disengage the platen, push the Carr Restore button to skip until channel 1 on the carriage control tape has a hole, with the paper manually lined up for the first line of printing. Re-engaging the platen synchronizes the physical paper forms with the carriage control tape. 

When I put the front plate and knob back on the lever, it was frozen again. A part had been broken because the knob itself was cemented in place so firmly that someone had snapped a bit of metal trying to turn it. I will need to think up a fix for the broken part in order to have the knob, now freed up with clock oil, work as it should. 

WORKING ON CB SWITCH CONTACTS

The goal of all my contact burnishing was to get the resistance of the switch down to a reasonable level. It was sitting around 220 ohms but when it touched the ohmmeter to the two sides of the contacts, it was much lower.

I realized that the resistance was elsewhere. Push in pins connect wires to the two sides of the switch and one was corroded enough to add the resistance. I removed the pin, cleaned it up and reinserted it. Resistance now about 6 ohms. 

REMOVED OXIDATION ON INTERPOSER SWITCH CONTACTS

There is another set of contacts in the carriage, which turn on when the interposer magnet has fully attracted its arm. The interposer magnet is used to switch the clutch that will be activated when the clutch magnet is energized, switching from low to high speed operation. The switching mechanism needs to have fully engaged before the clutch magnet operates, thus the interposer switch sends feedback to the printer control logic in the IBM 1130 when the switching is complete. 

I burnished for a couple of minutes and had a great low resistance connection when the interposer mechanism had fully pulled back (as it would when the interposer magnet is switched on). 

WORKED TO LOOSEN UP GEAR TRAIN

This was the big problem in the carriage. I kept at it, flowing the clock oil everywhere I could reach and turning it by hand. Suddenly, I felt whatever glue like material was inside give way. The gear starting turning very easily. 

MOTOR TESTED WITH BENCH POWER, CARRIAGE MECHANISM IS WORKING OKAY

I hooked up the 48VDC from a bench power supply to the carriage motor and turned it on. The motor spun right up and turned the continually operating parts of the gear train. When I manually pulled the clutch magnet armature, the carriage advanced a line with the detent falling into place. After I held the interposer magnet mechanism to the switched state and then manually pulled the clutch magnet, the platen turned faster and without detents. 

PREPARING TO REINSTALL THE CARRIAGE IN THE PRINTER

The carriage is fully functional other than the broken part that disengages the platen when the front knob is turned. I can repair that with the carriage mounted on the machine. I put on all the covers and got the carriage ready to move over to the printer for installation. 

Reassembly of the 1132 printer - part 3

INSTALLING DETENT LEVERS

The Print Clutch Detent Levers rest in the notches on the cams to keep them from rotating from this rest position. While the Print Clutch Latch is holding the Print Clutch Dog so the tooth is out of the Print Clutch Shaft flutes, the cams should be sitting with a notch on their perimeter in position for the Print Clutch Detent to fall into the notch and keep the cam from turning.

The bar holding them attaches down high on the frame on the front side of the printer. The bar is a very tight machined fit between the frames, requiring quite a bit of finessing to slid the bar between the frame sides and move it up to the mounting position. I had to tap the bar with a hammer to move it around to line up the threaded holes that bolts will screw into. 

The Print Clutch Restore levers are next up. These are even more difficult to start between the frame sides, as the surface rust on the frame sides meaningfully tightens the clearance between the restore assembly and the frames. I ran out of time fighting with this by the end of the workday. 

Restore lever assembly

Space into which it is installed - about 65% up vertically in the picture

Restoration of the 1132 printer carriage mechanism - part 1

LOOSENING UP THE SHAFTS AND BEARINGS OF THE GEARBOXES

The carriage motor runs continuously as does the main printer motor. A worm gear on the end of the motor turns parts of the gearbox, so they are always turning as long as the motor switch is on. 

Continually turning parts marked in green

The left and right side gears marked in green across the center of the picture above turn at different speeds. A clutch mechanism attached to each gear can couple its motion to the center gears. When either clutch is activated, the platen begins turning at the speed dictated by the left or right gear. The right gear turns the platen at about 150 RPM while the left gear makes the platen turn at 70 RPM. 

Gears marked in yellow turn in slow speed mode

Gears marked in red turn for high speed mode

When either the yellow or red gears are turning, they also turn the platen through a driving gear and a second detent gear ensures good vertical line alignment. 

A detent gear in the gear box has notches in it at each print line position into which a spring loaded detent lever will fall. This ensures that the platen stops precisely at the next line position even if the solenoid deactivation is somewhat imprecise. 

I worried about clearing up the clutches as they are somewhat complex with plenty of spaces for lubricants to freeze up the works. 

exploded view of a clutch

I have been seeping clock oil everywhere I can reach but not getting a significant improvement in turning resistance. This is going to take some time and might require substantial disassembly. 

MOTOR TEST

The 48VDC motor wouldn't turn with the very sticky gear train connected, but once I pulled the worm gear off of the motor, it spun up nicely with my bench power supply. It is a 50W motor but when free spinning it was consuming around 32W. I tried to get some clock oil seeping into the front bearing of the motor, hoping it spins even easier in the future. 

Worm gear removed

shaft ready to spin when 48V applied

CB RESTORATION

The CB (cam driven switch) consists of a cam gear that is on the same shaft as the carriage control tape drum. It has slots for each line position of the platen.

CB microswitch

The microswitch has a spring loaded plunger on the top which rides on the cam gear. The purpose is to send a signal back to the 1130 printer controller logic every time the plunger enters a slot. The printer controller logic activates the solenoid to activate a clutch. That causes the platen to start rotating at about 70 RPM. When the plunger falls into the next slot on the cam gear, the printer controller releases the solenoid so that the platen comes to a stop.

The plunger needed to be freed up to move in and out of the slots. Once it did, I concentrated on the conductivity of the contacts. After thirty minutes of work, the resistance of the points was still above 220 ohms. The corrosion from the rodent urine soaked really deeply into the contact metal.