Disk drive cleaning and restoration efforts - part 1

CONVERTED RUST ON MOUNTING POLE AND SPRINGY STEEL PIECE

I pulled off one of the poles that had rust pitting and the springy steel piece that holds the cartridge entry pivots. They had serious rust damaged. After cleaning and wire brush removal of loose rust, I applied some Naval Jelly to convert the rust to a safe alternative. I still need to do the other side, plus the screws are still rusty. 

FURTHER CLEANING OF THE DISK ARM AND HEADS

I did some more cleaning of the disk heads and arm, finding more evidence that there is no corrosion on these critical components. I used 99% pure isopropyl alcohol on lab tissues to clean off the surface of the two heads. They will need more work with cotton swabs and IPA before they are really clean, but I can already see that while they show signs of some wear they are not damaged beyond use. 

Arm material is in good condition

Lower head seems in decent shape

View of upper head shows no obvious damage

OPENED FILTER BOX, DISCOVERED MAJOR RODENT HOUSING DISTRICT

There is a plate on the bottom of the drive which encloses the HEPA level air filter and plenum which produces air clean enough to blow past the heads while they are flying over the disk surface. Considering that a typical dust particle is many times larger than the flying height, cleanliness is essential. 

I guess I shouldn't have been surprised, but this was jammed full of the wool like nest material and all the small nut shells left behind by the squatters that infested this machine. While the more accessible areas of the machine had the nesting material and shells removed long before it came to me, any place like this which requires substantial disassembly to reach is going to be filled like this. 

After I removed the mess you see above, I could see that some has reached into the air blower thus I will have to partially disassemble that to clear out the foreign debris. 

New cord installed, line filter closed up, almost done unwiring the sequencer box

LINE FILTER BOLTED DOWN AND COVERS INSTALLED

The new cord is wired into the line filter and everything is closed up. It is ready to be plugged into the building power once the sequencer box restoration is complete. 

making connections

SEQUENCER BOX PARTS AND WIRE BUNDLES ALMOST COMPLETELY REMOVED

I continued to strip parts out of the box and disconnect wires, with the aim of removing the entire damaged wire bundle so that I can copy it. I am almost done, but I have a balky screw holding the contactor onto the box. The convenience outlet has to be removed after that and all will be loose. 

The small terminal strip on the bottom, TB-7, had screws and posts that were so corroded by mouse urine that they couldn't be removed. The strip broke and will need replacement. 

Almost all out of box

PLENTY OF WORK AHEAD BUT THE END GAME IS A CLEAN WORKING POWER SYSTEM

I am pleased with the restoration of the raw DC power supply and the new power cord on the line filter. I believe that rock solid power is the essential base for a restored mainframe. 

Once I have a replacement wire bundle, I can begin the installation of parts and rewiring of the sequencer box. As far as I can tell from the visual inspection of the system, this is the last big item to undertake before I begin power testing. 

Working on disk drive, first giving it a good cleaning

FIRST STEP, CLEAN OFF THE DISK DRIVE

Although the drive looked really horrible, when I began to clean up sections I discovered that there are three main categories of impairment that cause the drive to look like it does. We have the foam insulation which became a black powder, there is some kind of oily film which is in turn holding dirt on the parts, and some parts have rusted. 

So far, the parts that have rusted are mostly secondary structures, such as poles to hold a cover on top of the drive, thus rust has no impact on their functioning. The one exception I can see is the main plate that turns the disk platter inside a cartridge has noticeable rust on its surface. Loose rust poses a huge risk for head crashes, thus I will need to convert and seal the rust on this particular part to make things safe. 

I have wiped away the power and the oily dirt from part of the drive already and was pleased to see how nicely it cleans up. The only visible degradation will be the rusty parts and I can deal with them. 

Result of just a little cleaning

I checked key parts such as the disk arm mechanism and found they had no lasting corrosion after I cleaned off the surface contaminants. In the picture above, you can see the rusty parts - a vertical pole, the spring holder to its left and the rotor that spins the disk platter. 

Finished cleaning raw DC supply, assembled and tested it; partially reinstalled line filter

REMOVING FINAL DIRT, GREASE AND MOUSE URINE FROM THE DC SUPPLY

Everything else had been cleaned. I wiped off the transformers and then wiped down the length of all the wires to remove any surface grime. The wire brush treatment had removed the thick brown areas to the point that I didn't think I needed any further cleaning or treatment of the metal. 

REASSEMBLY OF THE SUPPLY

The metal enclosure has markings with the capacitor numbers that match the schematics. Since I had stacked the capacitors in the same relative position as I removed them, that was really just a backup verification. The holes in the box also hint at the part placement. Finally, I had my pictures from before it was disassembled to guide me. 

I found that I had to back up a couple times to work out the best order to install parts in order to reach the spots for every screw to be reinstalled. I used the schematics as a check for the wiring which for the most part is obvious because all wires are cut to length and sitting in the proper position. A bit of beeping out with the VOM was the last check.

SET UP FOR BENCH TESTING THE SUPPLY

It will be some time before the sequencer box is rewired and operational, but I can test this unit out of the machine right now. I set up a step-up transformer to give me 230VAC that I could wire to the primary of each of the two transformers. The design of the supply is modular enough that I could test portions at a time, one transformer and then one voltage output section. 

One of the transformers is a ferroresonant type, which takes advantage of some magnetic properties to make a transformer whose output voltage is almost unchanged as the input voltage swings up and down. It has a separate primary winding with a capacitor, producing a resonant circuit that puts the magnetic field of the transformer in an oscillation that almost completely saturates the laminated iron core. This leaves little opportunity for primary voltages swings to change the magnetic field, thus the induced voltage in the secondaries is almost unchanged. 

This transformer is used to generate the +12V and +48V DC power. There is no additional regulation. The outputs come from a half-wave rectifier and some filter capacitors. Each output is isolated from the other and fused. The supply also generates 24VAC across two terminals for use by the Serial Communications Adapter (SCA) option to produce its RS-232B voltages, although this machine is not configured with SCA. 

Modular section for 48VDC

Modular section for 12VDC and 24VAC

A second transformer is an ordinary type, since the voltages produced by this transformer will all be passed through regulators that ensure stable and precise voltages. The ferroresonant transformers are bigger, heavier and burn more power than a traditional supply, thus only used where the regulation is needed. It is not necessary in this section.

This supply must simply provide 7.8VDC to the regulators producing +3 and -3, as well as 12VDC to the regulator producing +6V. It also has an output of 7.8VAC whose two legs are used as a bias input to the +3 and -3 regulators, respectively. These are also half-wave circuits with filter capacitors for smoothing. They do not have fuses in these circuit, but the regulators that consume the power have circuit breakers. 

RESULTS OF THE TESTING

I connected an autotransformer, a device that plugs into the wall and produces a range of AC output from 0 to 130V, to the input of the step-up transformer, thus I could swing the input voltage to observe the intrinsic regulation of the +12 and +48 outputs. I saw raw voltages of 14 and 52 with the nominal 230V input and the variations as I moved the input up and down was very minor. In fact, the output peaked when the input voltage sagged to about 205V but the changes were very small. 

I disconnected the autotransformer when testing the other transformer's circuits as it is not regulated in any way. At nominal 230V input voltage, the sections were producing about 9VDC for two sections and 13V DC for the raw supply for the +6 regulator. There was also AC across the bias contacts and 26VAC on the terminals that would feed an SCA were one of them part of the configuration. 

This supply is ready to be energized when the rest of the 1130's power system restoration is completed. I reinstalled it in the machine but left the regulators unconnected. This means we will not generate any SLT logic voltages and therefore the sequencer will not delivery the 12 and 48 either. I will be able to verify one more time that the voltages are all correct and in the proper polarity before moving forward.

MACHINE HAD BEEN WIRED FOR 208VAC, MUST CHANGE OVER ALL SUPPLIES

The jumpers tell me that this machine had been configured for 208VAC which is a connection across two phases of three phase service. It will be used with 240, single phase. The various power supplies in the 1130 system have jumpers to configure them for 120, 208 or 240. There are quite a few places where the jumpers must be switched, even inside the tamper resistant usage meter power supply. 

REINSTALLING THE LINE FILTER AND NEW POWER CORD

The line filter box was put back inside the 1130 and the wires reconnected from the machine to the filter. I have a new power cord fitted, with the two hot leads already installed. To finish this, I have to connect the ground wires on both sides, which completes the fastening of the filter box since the same nut that fastens the box also provides the ground connection. When the two top plates are reattached it will be ready for power as soon as I finish the restoration of the sequencer box. 

Disconnecting wiring bundles from sequencer box - part 2

BUSY FEW DAYS, LESS TIME IN SHOP

I guided visitors around the Space Force Museum at Launch Complex 26 today in one of my scheduled volunteer commitments. We had bigger than normal crowds with so many here for the final Delta program launch tomorrow - a Delta Heavy will launch a National Reconnaissance Office mission.

My return home was slowed when the used fairings were being trucked back onto base, requiring traffic to stop for a while. 

I also have visitors coming tonight and will be spending time with them over the next few days, which cuts into my time cleaning rodent filth, dirt and rust. Still, I did get to the shop and invested a couple of hours today. 

I discovered that with a wire brush, I could get the thick sludge off the raw DC power supply enclosure, thus it will be ready to reassemble after I clean off the remaining wires. The line filter box is also cleaning up sufficiently to begin assembly. I only have one portion of the line filter which has rusting that must be treated with Naval Jelly. 

DISCONNECTING COMPONENTS IN THE BOX FROM THE BUNDLES

It was time to unwire parts inside the box to free up the bundles and remove them. This did require removing terminals from devices such as the contactor and circuit breaker, but I was able to detach relays, switch, time delay, convenience outlet and fuse holders so they could remain connected to the bundle for now.

DISCONNECT BUNDLE FROM TB1 AND THE SMS CARD CONNECTOR

I pulled the connections off the SMS connector that holds the power sequence logic. In addition, the bundle was attached to multiple points on TB1. Fortunately, the bundle wires run to the top row of screws of this horizontal terminal block so it was very easy to disconnect them.  

I believe I will be able to pull the bundle I just disconnected inside the sequencer box, which gets me very close to having the bundle loose for replication. 

Disconnecting wiring bundles from sequencer box - part 1 disconnecting TB3 and TB2

WIRING IS MOSTLY CONNECTED TO TERMINAL BLOCKS INSIDE AND BEHIND THE BOX

There is a small terminal block TB7 inside the box which is only used with the small transformer T1, also inside, that generates the 24VAC used for EPO and power switches in the 1130 system.  Another terminal block, TB2, is used for internal connections such as to the relays, fuse holders, and so forth. 

There are terminal blocks outside, TB1 on the rear, outside, and terminal block TB3 on the left outside of the box. All AC voltages in the machine are controlled from here. Connections run from relay R3 inside to transformer T3 outside that powers the convenience outlets, and to transformer T2 outside that drops 230VAC to 115VAC for use by peripherals and the fans. 

The SMS card that implements the power sequencing is wired to the sequencer box. As well, TB3 brings the SLT logic voltages for sampling in the SMS card and passes the +12 and +48 through relay R2 inside the box. Finally, TB3 provides the power on reset signal to the logic.

Many peripherals are provided AC voltages through their power connector. These are wired from the cable connector panel and the SMS power connector panel into the sequencer box, either outside on TB1 or inside on TB2. 

DISCONNECTING THE 1442, 1132 AND 2501 POWER CABLES

Fortunately, the wires that bring power to the power receptables for the peripherals were on separate cables that entered a different hole in the rear of the sequencer box. They were undamaged by the mice and therefore can be used. This saved me from having to pull pins out of a connector and replace the wire.

TERMINAL BLOCK USAGE IS VERY DISCIPLINED WHICH AIDS DISASSEMBLY

The terminal blocks have pairs of screws for each position, sometimes with jumpers between adjacent pairs in more than two screws are needed. IBM has assigned the right side of TB2 and the top side of TB3 for wires connected to the bundles that pass through the box walls. This is very convenient because removing just one side of the strip frees up the bundle nicely for eventual removal. 

DISCONNECTING THE WIRES FROM TB3 THAT RUN INSIDE THE BOX

These wires from the top row of screws on the horizontally mounted terminal block TB3 go inside and join the main bundle running through the box. Eventually these are connected to devices in the box or run back outside through the hole in the rear. I was able to pull that portion of the bundle through the side hole and it is now inside the box with the rest of the bundle. 

DISCONNECTING THE WIRES FROM TB2 THAT RUN OUTSIDE THE BOX

The right side screws of the vertically mounted terminal block TB2 were connected to the bundle that was going to run outside the box. There were also wires from outside connected to the left side terminals 3 and 5, coming from transformer T2. 

I still have to disconnect the other end of the bundle going out the rear hole. Some wires in the bundle run directly to the SMS power connectors, and the primaries of transformers T2 and T3. Depending on the connection methodology, they get unscrewed or unsoldered. 

The connections to devices such as relays inside the sequencer box are also part of the big bundle - the wiring harness. I have to get these disconnected in order to free up the harness entirely. 

Eventually the wiring harness will be removed from the machine and serve as templates for the manufacturing of new bundles with the same layout and lengths. 

Finished disassembly and did more cleaning of the raw DC power supply

REMOVING DIRT, GREASE AND MOUSE URINE FROM THE DC SUPPLY

I removed the remaining capacitors from the enclosure. I then unmounted the transformers in order to clean the bottom of the box. I swept out the dirt and the many shell fragments of the small nuts that the mice were dining on. 

NEED WIREBRUSH AND THEN RUST CONVERSION TREATMENT

The stains are so thick in places that I just can't get though it with paper towels and cleaners. I will be receiving wire brushes this evening and will use those to get the sediment out of the box. I then will use a treatment to convert any rust to an inert compound that will seal and protect the box. The product I am using is a gel which can be completely washed off, not a liquid that might seep into areas and continue interacting. 

PLAN FOR MORE CLEANING OF THE TRANSFORMERS AND WIRE INSULATION

There is a coating on the insulation of all the wires in the box which I will clean off with 409 and paper towels. Not too aggressive, but clean it up quite a bit. I will also wipe around the transformers and visually inspect them. 

Replacing severed power cord - part 1, the removal of the line filter

POWER CORD WAS SLICED OFF AT SOME TIME IN THE PAST

When the IBM 1130 was rolled into my shop, its main power cord was missing. The cable was sliced off close to where it entered the line filter at the base of the machine. Sometimes this takes place when a machine is decommissioned and either given away or sold to a salvage operator, to limit liability for any injury if someone were to power up the system. It may also be done in a museum if they wish to eliminate the risk that someone will plug in a system that is not known to be in safe working condition.

In any case, this means that I have to install a new cable suitable for 240V. The 1130 main circuit breaker is 20A and the connector onto the line filter for the main power cord is a Russell and Stoll RS3720, a 20A connector with three round pins and a ring that screws onto the receptacle on the line filter. 

The power consumption of the 1130 itself (the processor box is an 1131; when considering the 1131 plus all attached peripheral boxes, the system becomes an 1130) is 1500W thus under 7A of draw. However, the peripherals receive their AC power from the 1131 which adds the requirements of card readers, line printers and other devices which is why the cord and circuit breaker support 20A total. 

There are a number of different plugs that support 240V 20A or 30A that can be attached to the building side of a power cord, the other end having the RS3720. I tend to use either NEMA L6-20P or L6-30P depending upon the outlet into which I will plug the 1130 system. 

A line filter sits between the power cord and the rest of the 1130. Its purpose is to filter out any electrical noise generated by the 1130 system so that it doesn't feed back into the building circuitry and cause interference with other electrical devices. 

LINE FILTER CORROSION ON FITTINGS AND DIFFICULT TO OPEN

The RS 3720 connector onto the line filter box was so corroded that I couldn't full unscrew it and remove the stub of the power cord. I had to disassemble the line filter partially to reach in and snip off the wires from the female RS3720 into the filter, just to remove the male connector and cable stub. 

The line filter box has plates on the top fasted with six small 1/4" bolts each, but with the bolts removed the plates did not budge. Likely they are corroded in place. The overall line filter box is mounted to a welded plate on the bottom of the 1131, using studs with nuts on both ends. One end of the stud fits through the welded plate and I could reach those nuts. The other end apparently terminates inside the line filter box rendering those nuts inaccessible with the box still sealed.

I attempted to unscrew the nuts from the bottom but the studs begin turning once they become slightly loose. Worse, for two of the four studs, turning it to try to unscrew it seems to be twisting internal wires around the stud, probably ground connections, because I can feel the increasing resistance of the wire stopping my rotation. 

I applied some percussive maintenance to the cover plates and they finally came loose. I was able to remove the wires and the line filter box from the machine. It appears to be in good shape, with the actual filter components hermetically sealed in the center section. 

Delightful patina

CLEANING BEFORE REINSTALLATION

I did some initial cleaning of the box but the gunk, a mix of dirt and rodent excretions, is stubborn. I have some wire brushes coming tonight and will use those to attack the worst of the coatings tomorrow. It will be an easy matter then to install the new line cord. I have to buy a cord fitting that fits the opening of the existing box, to secure the cable I bought. 

Disk drive on bench, raw DC power supply on bench, no new issues found

I FINISHED UNMOUNTING THE DISK DRIVE AND MOVED IT TO THE WORKBENCH

I have great access now to the disk drive for cleaning and restoration. As a bonus, this opens up the congested area of the 1130 where power and signal wiring is clustered. It allowed me to look over all the wiring for any signs of damage; it appears that the only gnawing took place in the power box (sequencer box).

Mess of wiring in the base

Space to look at all the wiring

COULD SEE THAT THE RAW DC POWER SUPPLY WAS ALSO IMPACTED

As you can see when looking at the back of the raw supply, it is open and I could see quite a bit of dirt inside. The top grate has holes which would allow rodent urine to enter, but with the rear wide open there was the chance that mice entered and did some chewing.  

RAW POWER SUPPLY PULLED AND PUT ON WORKBENCH; FILTHY INSIDE

I unwired the supply, removed it and had it on the workbench for a full inspection. It looked terrible in there, dirty stains covering the parts as well as bits of mouse bedding and plenty of plain old dirt sitting in the bottom and atop everything. 

Even more room now

READY FOR THE SEQUENCING BOX REWIRING

I picked up 12 gauge stranded wire in both black and white insulation colors, which should give me enough to rebuild all the damaged wire bundles in the machine. I anticipate that in a day or two I will get into the sequencing box itself, documenting and removing the damaged existing bundles. With those in hand, I can build good replacements. 

STARTING TO CLEAN AND CHECK ALL THE COMPONENTS INSIDE RAW DC SUPPLY

I began to remove components, cleaning them and checking the capacitors for signs of problems. The disgusting state of everything in the power supply enclosure made this an unpleasant task indeed. I could get the majority of the stains and dirt off the components with some 409 and elbow grease and lots of paper towels. 

Right one before cleaning, left after some scrubbing

My capacitance meter showed all the capacitors were at or substantially above the specified values. I did a quick ESR check on a couple and they seemed acceptable. This has been my experience with the capacitors used in IBM equipment built in the 1950s and 1960s - age has no effect on them at all. 

I then inspected one of the two transformers for any signs of damage to the windings. It appears to be in great shape, other than some surface rust on the laminated iron plates. I did a bit of cleaning of loose rust from the laminates but I won't clean them any more aggressively. That would risk introducing conductivity between laminate plates, which causes parasitic eddy currents and heating of the transformer. 

BATTLING WITH LINE FILTER AND POWER CORD STUB

The connector body where the severed stub of the power cord enters the line filter box is so corroded that I couldn't unscrew it properly. I am also having difficulty getting the line filter box out of the machine for inspection. The parts catalog suggests that it is bolted to the machine bottom from the inside of the box. Since I see no way to get into the box as it sits, I could only turn the nuts under the machine. These turned a couple of rotations and then seemed to be winding wiring because the resistance to turning went up fast. 

Line filter under the wires

It is likely that I will remove this entirely and substitute a modern line filter in a metal electrical box. Line filters are only around $25 and I won't be dealing with corroded parts. 

SOON - THE SEQUENCER BOX ITSELF

Top of sequencer box, mice chewed through rear

The bundle of wires you can see above going to the rear of the sequencer box are mostly connected to the terminal blocks on the rear. Other connections to the terminal block run inside the box and those are the wires which were gnawed by mice. 

Missing main power cord and a few small issues spotted but generally the system is in good shape

BEGINNING ON THE RESTORATION, LOOKING CLOSER AT EVERYTHING

I removed most of the covers and began to inspect more closely to be certain there arent any show stopper kinds of damage before I start spending money on parts and supplies. The SLT cards look pristine, the backplanes and all the signal wires look great. 

I did find some spots with evidence of sustained rodent urination leading to rust and corrosion. The bracket that supports the SMS card connectors where the disk drive power, typewriter power and the console printer signal lines are connected was one such place. I noticed that the contacts for one of the console printer connectors were tarnished due to the contamination. That is repairable.

The power box was already identified, but the usage meter power supply box also shows serious urine induced rusting and warrants internal inspection. We had also spotted the rust inside the disk drive. So far, nothing else has popped up. I will be removing the main power supply (raw DC voltages) and inspect it since it has a metal grill top and therefore the insides could have sustained damage. 

The cover on the top of the machine can be rotated to the right to gain access to the CE switches such as Lamp Test. It is hinged on the right side of the machine and has a support bracket to keep it from torquing sideways as it is moved. That bracket was damaged and disconnected sometime in the past. A part should slide through a channel but it likely became stuck with gummed up lubricants. Applying way too much force causes it to bend and then have to be disconnected. I believe I can reshape and repair it. 

support bracket needing repair

MAIN POWER CORD WAS SLICED OFF AND MISSING

I was surprised to find that the main power cord which would have been plugged into the building power is completely missing. Somebody sliced it clean off at the point where it enters the line filter on its way into the 1130. 

Copper has gotten a bit expensive in recent years, but even with all the power box rewiring and a new 30 amp cable this won't be a deal breaker cost. 

REMOVING DISK DRIVE DUE TO EXTENSIVE RUST/DIRT REMEDIATION

I will completely remove the disk drive and get it onto a workbench as it must get substantial work to remove all the dirt, the seed remnants, the rust and any corrosion caused by animal excretions. I inspected inside the SLT card cage on the disk drive, with no signs of damage from incursions. 

The cards should be held in place onto the backplane by the plastic bar you see across the top. It should snap into the plastic fingers at top and bottom but the plastic has aged and snapped off. This is not unexpected. IBM chose materials for their mainframe products built in the 1960s that all degrade badly with time. The oil and grease turn into sludge or glue. The foam soundproofing either crumbles into a powder or reverts to an oily mass. Plastics loose their plasticizers and break. 

The removal of the drive does give me better access to the power and cabling area deep inside the machine where I am doing rewiring. With all the signal lines for the peripherals passing through that area, a careful look is warranted. 

Beginning the removal of the drive

As I disconnected the disk start switch at the front of the machine, I discovered that the bar on which the switch is mounted was only connected to the 1130 frame with wire lacing cord, not the necessary bolts and nuts. 

A bolt and nut belongs here

A few wires left and I can lift it out onto the bench

Power before all else

THE POWER SYSTEMS IN IBM MAINFRAMES ARE COMPLEX

IBM systems make use of a diverse range of voltages, in part to leverage existing subsystems and designs. Thus, the IBM 1130 and 360 systems mixed SLT circuitry with sections built with the predecessor SMS technology and components built originally for vacuum tube based products. That introduces a laundry list of voltage requirements and the result is a surprising number of different power supplies.

Main frame of 1131

Memory expansion frame (blister)

Our first attention was strictly on the power box that manages the high voltage AC. Already you see that IBM might have a 230V machine but power some components such as fans and the convenience outlets at 115V. In addition to that, the box produces 24VAC which is used to drive power and emergency stop buttons/switches.

The box itself is the 1131, by the way, because an 1130 system is the 1131 plus peripherals - including 1132, 1442, 1055, 1134, 1627, 1133, 2310, 2501, 1231, 2250, 1403, 2420 and others.  The mix of product numbering schemes reflects the leveraging of boxes from other systems. The 1627 plotter was originally developed for the 1620 system. The 1442 reader was originally developed for the older 1440 system. The 2xxx boxes were developed for 360. The 1055 was designed originally for an older communications product family that included the 1052 and 1053 typewriters and even a card reader mechanism that morphed into the 1442. 

One other major AC voltage used in the system is 7.25VAC for many of the light bulbs in the system. However, even then, some bulbs were 12VDC or even 48VDC depending upon the circuit driving them. Not only are we distributing 115, 230, 24, 7.25, 12 and 48 inside the 1131, we may be delivering some or all of those voltages over cables to peripheral boxes. 

The we need to provide power for the logic circuits. SLT logic (30ns family) requires three DC voltages - +3, -3, and +6. SMS logic can require +6, -6, and +12V and others. Solenoids are typically 48V. Pushbutton switches tend to use 12V which is the voltage level of the slowest SLT family, as that gives more margin to handle a bit of contact corrosion and increased resistance. 

Core memories have their own voltage levels and the two different core memory designs used in the 1130, SJ-4 for 3.6 us and SJ-2 for 2.2 us operation, had different requirements. The blister extension frame that holds larger core configurations or any SJ-2 memory has its own sequencing box and can have its own power supply. There can be a -15, a +6 and a +3 depending on memory type, the main power supply type (MPS versus midpack) and the memory capacity.

The Synchronous Communications Adapter uses RS-232B signaling levels thus an additional -12V supply exists in 1130 systems with the SCA feature.

The usage meters have their own 40VAC supply in a tamper resistant box. 

MAIN DC POWER SUPPLY - UNREGULATED

The midpack power supply, distinguished from the earlier Midrange Power Suppy (MPS) set of power supplies in older 1130 systems, produces unregulated DC. It also outputs 24VAC that the SCA gate will convert to +12 and -12VDC. There is a 7.8VAC output but that is fed to two of the DC regulators as a 'bias level'. 

The midpack supply is not completely unregulated, as the transformer that generates the +12 and +48V levels is ferroresonant, thus line voltage swings have little effect on the output voltage. However, the other transformer in the supply that will ultimately produce +3, -3 and +6 is unregulated. 

VOLTAGE REGULATORS FOR LOGIC VOLTAGES

Three massive voltage regulators are used to convert the raw unregulated voltages from the midpack supply to the precisely managed +3, -3 and +6 for the SLT logic. These have an adjustable regulator card and a crowbar card, based on SMS technology as these are derived from the SMS era supplies of machines like the 1401. The crowbar will short the outputs causing the circuit breaker to open if the output voltage of the supply gets above a target level, in order to protect the SLT cards from overvoltage damage. 

The voltage regulators use Germanium power transistors in parallel banks to support the current capacity of the regulators. The +6V supply is rated at 24A while the other two are 20A ratings. One common failure mode of the IBM 108 power transistor is to become an open circuit, thus the other transistors carry more of the load. The supply at low load appears to be working properly, but begins to sag as it approaches its full load rating and can cause cascading transistor failures. 

Therefore it is essential to build a test for the regulators that will draw full load, that is the only way to be assured that the regulator is working properly. It would have been nice to own an electronic load that could be dialed to 20 or 25A of load, but I don't have that luxury. 

I use banks of power resistors in series and parallel to achieve the target resistance that will consume the rated current. For the 3V regulators, which can supply up to 20A, we need a net resistance of 0.15 ohms that can dissipate 60W in total. The 6V regulator requires 0.24 ohms net resistance and must handle 150W of power for short periods of time. 

RELAYS INVOLVED IN SWITCHING SOME OF THE DC VOLTAGES

The power sequence logic verifies that we have good levels on +3, -3 and +6V before it allows the rest of the circuitry in the machine to receive the other voltage levels. Thus, a relay controls +48 and +12VDC to the machine. One symptom of a dropped logic voltage level is that the indicator panel lamps to the left of the keyboard do not  light, even ones like Disk Unlock or Forms Check that one expects. 

Relays also switch the voltages to core memory, so that we don't effect any data with random signals if the SLT logic is not properly powered. These tend to be documented on whatever page had free room when the engineer was tasked with drawing them, often nowhere near the rest of the circuitry that either drives the relay or consumes the switched power it controls. Nothing new here, this is a common deficiency in IBM documentation, that it is technically correct but may be unhelpfully obscure. 

POWER SEQUENCING LOGIC

An SMS card that sits just outside the main power box implements the power sequencing logic for the system. There are a series of three reed relays, each energized by one of the main SLT power levels. The contacts are wired in series to power a relay (R1) that energizes when all SLT voltages are present.

Only when R1 has energized is relay R2 activated, to provide the +12 and +48VDC to the other circuits of the 1131. Relay R1 also has contacts that are part of a safety circuit to lock out the machine from powering up if it had dropped an SLT voltage during operation.

The lockout circuit involves a time delay relay TD1 which will cause a lockout reed relay RR1 on the SMS card to energize if R1 is not on at any time. If one of the voltage levels is off before you first power up the machine, the only consequence is that R1 and R2 don't engage and we have a machine that won't do anything. 

However, if one or more SLT voltages drop after TD1 is energized, it fires RR1. RR1 has contacts that will keep it energized even when the system power switch is turned off. As long as the main circuit breaker of the 1131 is turned on and the plug is inserted, RR1 locks out the power switch from operation. The symptom of this is a machine that won't turn on. A CE Reset switch can turn this off, or flipping the main CB, or unplugging the machine. 

I believe the logic behind this is that one of the voltages dropping during operation might have been due to the overvoltage protection, when the crowbar card forced the regulator CB to trip off. If the regulator is producing dangerously high voltages, we don't want customers switching the machine on repeatedly to try to get it to come up. 

That is why this is effective if R1 had picked due to good levels and later it drops, but they are less concerned if the regulator doesn't come up initially since that is not a symptom of an overvoltage fault. The power sequencing card also ensures that when the customer flips the system power switch off, it first drops +12, +48 and core memory voltages while the regulators are still delivering good SLT voltages. Thus we are protected from random signals from SLT causing issues with core or solenoids in peripherals. 

For machines with the blister frame installed, there is a second SMS sequencing card that is used to drive a relay B in the blister that won't deliver +12V to the core unless SLT power is good. 

EPO SWITCHES AND THE 1133 COMPLICATE THINGS

For safety reasons, IBM systems have an Emergency Power Off pull switch on the console. That will drop power immediately across the system. Unlike the system power switch, which leaves the 115VAC convenience outlets powered up when the system is off, the EPO also drops power to the outlets. 

The 1133 Multiplexer box is an expansion for the 1130 system containing circuitry to attach peripherals such as the 1403 printer, 2310 disk drives and others. Since the 1133 handles peripherals that need 3 phase power, such as the 1403 printer, it is the primary power connection for a system that has an 1133, and the 1133 will feed AC power to the 1131. The building power connection is to an 1133 when it is part of the system otherwise to the 1131. 

Because of its role supplying overall power to the 1130 system, the 1133 has its own EPO pull switch in addition to the one on the 1130 console. These are wired in series. The 1133 also supplies the 24VAC to the power and EPO switches, not using the 24V output of the midpack power supply. 

Beginning restoration of main power box in Infoage IBM 1130

OVERVIEW OF RESTORATION PROCEDURE

The main power box is the enclosure for the main system circuit breaker, the power controlling relays, the time delay reset relay, the fuses, a contactor, a small transformer and the main AC interconnection terminals. It sits under the disk drive on the right side of the machine. 

This system had evidence of a rodent infestation that left many wires with insulation gnawed completely off, some remaining cotton nesting material, and rust/corrosion at the bottom of the box that appears consistent with the effects of urine. There is unknown effect on relay windings and contacts, but nothing was obviously damaged. 

I don't want to try to patch wires around with so much damage and the potential for other spots that I can't see where the insulation is damaged or split open. The safest thing is to completely rewire the box. 

IBM laced their wires into one major bundle where every terminal naturally falls next to the screw where it will be affixed. The wires stay together as a rope which is far preferable to a 'rats nest' of individually routed wires. Smaller bundles are also used, such as the neutral wires running through a different opening in the rear of the box from all the hot wires. 

I will document and verify all the connections, then remove all the bundles and take them out of the box. They will remain intact as a template for the creation of replacement bundles. 

Other parts will then be removed and cleaned up, leaving the bare metal box. I intend to wire brush all the rust and corrosion away. I will then treat the rusted areas with Naval Jelly, which converts the rust into a solid that also blocks oxygen entry for continued rust formation. Once the box is in good shape, the parts go back into it so that everything is ready for wiring. 

MANUFACTURING REPLACEMENT WIRE LOOMS

My plan for building replacement bundles is to use the existing bundles as templates. Where damage makes that a challenge, I will have access to the intact bundles in my own IBM 1130 system that I can measure. 

Essentially, every connection in the bundle is a single wire with a terminal on each end, usually ring terminals. The existing bundle will show me the length of each wire, guiding me to cut wires just a bit longer and to put a terminal on only one end of the wire.

I will line up the wires with the terminals in the existing bundles, then begin lacing the wires into a new bundle. The goal is to have the terminals fit exactly to the destination screw, matching the IBM built part. 

As I reach the far end of each wire where it emerges from the lacing, I will match that to the second terminal on the existing bundle. Cutting my oversize wires and installing a terminal will produce the second terminal on the wire at the correct position to connect to its target screw. 

I should end up with a bundle that I can fit into the box where all the terminals sit over their destination screw. A check with a continuity meter will ensure that the terminals on one side reach the correct terminal of the other side. At that point, they are all screwed down on to their terminal blocks or soldered to their relays or other objects. 

TESTING THE POWER BOX

The goal is to step by step verify the correct delivery of power to the circuit that should be energized without powering any other circuit. I will walk you through a beginning set of tests to show the various paths that must be checked.

Main CB open

In the first case above, with the main circuit breaker open, no circuit in the machine should be energized. Every other terminal is tested for continuity to either of the input legs. 

Only the CB is on

In the case above where only the circuit breaker is switched on, but the fuse F5 is missing, we should not have any power delivered to the transformer T1 nor to any other circuit in the machine. 

CB on and fuse F5 is in

Now we deliver power to the first part of the machine. In this case, we energize transformer T1 which steps down the voltage to produce 24VAC. The 24VAC is only routed to the system power on switch and emergency power off switches. No other circuit should receive any connection to either leg of the input other than the primary windings of T1 and the secondary winding of that transformer should only be connected to the lines that run to the EPO and power on switches. 

At the same time as the CB is potentially energizing transformer T1, there is also a path down to energize transformer T3 for the convenience outlets on all boxes in the system. We will look at that below. 

CB on but relay R3 not activated

Unless relay R3 is activated, the power from the CB will not be delivered onward to transformer T3. R3 switches on when the 24VAC from transformer T1 is not blocked by a pulled emergency power off switch, whether or not the system power switch is flipped on. We have convenience power as long as the CB is on, normally.

CB and R3 but fuses F3, F4 open

The fuses at F3 and F4 have to be intact in order for the power to flow through the CB and through relay R3 onward to the transformer T3. It is only when all of those are present that the convenience outlets on each box have 115VAC power, stepped down from the 230 line voltage by transformer T3. 

power flows to T3 and onward to convenience outlets

If this path is active we should only have connectivity to the outlets and nothing else inside the machine.

T3 output to convenience outlets only

Meanwhile, the main contactor is what is required to deliver power to most of the rest of the circuits in the machine. It is activated when the system power switch is flipped on, delivering the 24VAC through the Emergency Power Off switches (as long as they were not pulled) to the contactor solenoid. 

Contactor must be turned on to deliver most power

Time Delay relay TD1 will allow the power on switch to energize the contactor but when it times out in a few seconds, if the power sequencing circuit did not detect proper voltages present from +3, +6 and -3 volt supplies, it will drop the contactor and turn off the machine. This is a very confusingly drawn circuit and hard to illustrate. The point is simply that the power switch turns on the contactor and it remains on only if the power supplies deliver good voltage levels. 

Contactor delivers 230 to rest of machinery

The contactor feeds 230V directly to a few peripherals that have fuse protection in their own boxes, such as 1442, 1132 or 2501. It also feeds transformer T2 directly, with no intervening fuses. T2 will step the 230V down to 115VAC which is used by devices such as the fan blower motors and any peripherals powered through the SMS power connectors. 

Note that you can see connections to some fuses. The fuses F1 and F2 feed the main power supply and F7 feeds the lamp power supply. Fuse F6 protects the 115VAC from T2 delivered to peripherals through the SMS power connector, which include the 1053, internal disk drive motor, 1134 and 1055 paper tape and the 1627 plotter devices. 

At this point the testing continues, essentially removing all but one set of fuses at a time and validating which circuits are energized and which are left dark. 

Most of this can be tested independently, except that we need the power sequencer to leave the contactor energized if we want power flowing through there to TB2 for fans and through Fuses F1, F2, and F7 to power supplies.