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. 

Reassembly of the 1132 printer - part 2

SUCCESSFUL LAPAROSCOPIC SURGERY ON PRINT CLUTCH CAM

There was one Print Clutch Dog that had slipped off its pivot point, which I deferred repairing until this point in the assembly. I had to remove the top guide bar/comb in order to bend the adjacent disk away far enough to nudge the dog back onto its pivot. It took about ten minutes to finesse it, but mission successful. The guide bar went back on. 

I didn't have much time today as I was at the Space Force Museum most of the time. 

Reassembly of the 1132 printer - part 1

BEGAN REASSEMBLY OF PRINTER MECHANICAL PARTS

I began assembling onto the frame the subassemblies I had worked on. I first installed the Print Clutch Cam shaft onto the machine with the Print Clutch Cams all resting in their idle position. This is where they will sit if the Print Clutch Dog is held out of the shaft flutes by the Print Clutch Latch lever. 

The cams are separated by the comb slots of the guide I inserted while working on the workbench. When I put the Clutch Print Cam shaft onto the machine, there was another comb guide at the bottom into which all 120 cams had to fit. This was a very slow and tedious process, taking about an hour of time to move them carefully to fit into the comb teeth before the shaft settled down in place on the frame.

Meshed at right, trying to get the rest into bottom comb

A couple of Clutch Dogs popped off their pivots

In the process of getting the cams into the bottom comb and installing the shaft, I ended up with a few of the cams rotated compared to all the others. I also had a couple Print Clutch Dogs pop off their pivots, which I will have to resolve with a 'laparoscopic surgery'. 

I finally had the full set of cams engaged in both top and bottom combs. A third comb was added at right angles, but that was a breeze now that the top and bottom of the cam disks were properly spaced.

All engaged, with the shaft ready to attach

Third comb bar added to further stabilize the cams

I installed the two bearing caps and tightened them down. There were a number of restraining screws to reinstall that keep bearings from walking out of the side of the frame.

I then reattached the ribbon mechanisms and other parts that had been removed when I took the bearing caps apart. The left and right ribbon mechanisms are connected by a bar that runs through the print machinery, between the Print Clutch Cam shaft and the Print Wheel Drive shaft. I got that squared away. 

shaft just visible going through hole in frame

Shaft emerges at the other side

Final tweaks to the 1130 core memory replacement (MRAM) board

FINAL VALUE CAPACITORS INSTALLED IN THE TIMING CHAINS

The updated capacitor values for the timing chains arrived, but very late. They were shipped Fedex ground with a scheduled delivery of Aug 14. Due to a string of missteps and poor execution, such as sitting 36 hours in some depots before moving, it finally was out for delivery on Monday August 18th.

I did receive the package by 1PM Monday, in time to still get over to my shop for a short time. I put these new timing capacitors on the board. I then installed all 17 of the bypass capacitors at each integrated circuit location. 

BEGAN ANOTHER ROUND OF TESTING. 

As I was verifying that the replaced chips output a negative going sense pulse when a bit being read was 1, I realized I had installed 74LS03 chips which have a minimum VCC requirement of 4.75V but my board operates on 3.3V. They were working properly however I ordered 74HC03 chips which work fine with 3.3V VCC and are the same footprint. I will replace the five output chips with the new 74HC03.

I was able to verify that the MRAM chip does store data and return it properly, at least for a default storage address. I used a bench tool to generate a positive pulse for storage read and for storage write, setting up the input data and observing the sense output of the board. 

I am going to set up a bit more elaborate test where I set various storage addresses, store different data patterns in them, and then read the addresses to check that these are discrete locations giving the associated data patterns. It still uses a debounced pushbutton to emit the read and write signals. All the timing on the oscilloscope shows it should operate correctly at 1130 speed. 

CABLED UP FINAL POWER CONNECTIONS

I put together the wiring between the power regulator module and my board, along with wires that will attach to the 1130 power supply terminal strip at the bottom of the gate where the memory compartment sits. They have ring terminals on them so that I can quickly hook up the memory when I am ready to test on the IBM 1130. 

SHIELDING BOX TO BE BUILT AND INSTALLED

I do plan to build a metal box to fit over the MRAM chip since it is sensitive to magnetic fields. I set up four ground pads on the PCB where I expect the box will be soldered down. The ground plane underneath the MRAM chip is unbroken as well. 

I found a good shielding box on Amazon that would fit reasonably well - a bit larger footprint but will clear other parts on the board. It is made of Mu-Metal, a material with high magnetic permeability that would strongly attenuate any changing magnetic fields outside the box. However, once it was ordered, the vendor confessed that it is not in stock and cancelled the order. The product listing remains on Amazon with the same unrealistic delivery estimates to lure the unwary. 

I may have to form my own box, which may challenge my skills with metal work given the limited tools I own for the purpose. However, if I can form the part up so that I can solder overlapped seams and it is not too misshapen or ugly, I could use that. I bought some heavy copper sheets, since MuMetal prices were near $100 in the minimum quantities they offered. 

FINAL STEP WILL BE CONFORMAL COATING OVER THE BOARD

I will coat the board with silicone to insulate and protect it while it lies inside the gate of the IBM 1130. However, I will wait until I have completed testing and won't need to change the board or any parts on it. 

Freeing up 1132 printer components - part 8

FINISHING THE PRINT CLUTCH LATCH LEVERS

The oil worked overnight and with just a bit more work, all the levers move freely. 

FINISHING THE PRINT CLUTCH CAM AND CLUTCH DOG WORK

Most of the mechanism in the printer is lubricated by spraying IBM #6 oil on the parts without disassembly. However, the flutes of the Print Clutch Cam Shaft should be lubricated with IBM #17 grease. I have modern replacements for these lubricants. 

Thus, I began from the right side, making sure every Clutch Dog pivoted freely, that the Print Clutch Cam rotated around the shaft when the dog tooth was not engaged, and then sliding it against the finished Cam disks. I would grease up a section of the shaft and then process Print Clutch Cams until I had mostly filled that area. Below is a picture with a section of the shaft having been greased, before working on the Print Clutch Cam disks to the left of it. 

The maintenance manual recommends engaging the comb to keep the Print Clutch Cam disks in their proper spacing. It is also supposed to keep any Print Clutch Dogs from popping off their pivots. I hooked up the comb as suggested, but my initial packing of the Print Clutch Cam disks was too tight together requiring me to massage the parts to fit in the comb. During that work, two Print Clutch Dogs popped off their pivots. 

I believe I can reset the dogs onto the pivots once the shaft is back in the machine, so I will leave the two dangling for the time being. 

It is time to reassemble the printer mechanism, adjusting as I reinstall to prepare it for hand testing and eventually testing hooked to the IBM 1130. 

CLEANUP AND TESTING OF THE CARRIER ASSEMBLY

The carrier assembly has an electric motor, a gearbox, clutches, two solenoids, and the carriage control tape mechanism. First up was a cleaning - removing nut shells and other infestation consequences. I then checked the lubrication and movement of the gear box and other key parts. 

The gear train is very stiff - solidified lubricants at work - and needs much work to free up the rotating parts. 

POWERING THE CARRIER WITH A 48V BENCH SUPPLY

The carrier motor runs on 48VDC as do the solenoids that engage either single space or skipping movements. I used a bench supply and testing the motor. It attempted to turn but the high friction of the gearbox was too much for it, even with 50W delivered to the motor. I will test again once I get the mechanical parts freed up. 

CARRIAGE CIRCUIT BREAKER (CB) FROZEN AND LOOKING CORRODED

IBM uses the term Circuit Breaker (CB) for a switch that activated by moving parts - either activated by cams or in this case by a plunger popping up and down in slots around a gear. The CB will send a pulse at each line position as the carriage moves - the slots are spaced to produce six lines per inch vertically on the print forms. 

The metal leads for the switch contacts look very corroded and blackened from the acidic rodent urine atmosphere. The spring loaded plunger is frozen in position up in a gear slot. I will have to free up the plunger motion and then either clean the contacts or replace them to get this key CB working. It is how the carriage knows to stop after spacing one line.