Nailing down configuration of IBM 1130 I am restoring, ordering new fuses

CONFIGURATION OF THE 1130 SYSTEM BEING INFERRED FROM CONNECTORS

Looking at the cable connections on the rear of the processor, I see only three connectors in place. The 1442 card reader/punch is served by two of them. The third location can be used for one of two different peripheral devices, depending on what is configured in the system; the 2501 card reader or the 1231 optical mark reader. 

The 2501 card reader also requires a power connector, thus if tthis machine had the 2501 and the 1442 it would have two power and two signal connectors but there are only two signal and one power installed. Therefore I infer that this machine was configured with the 1231 and 1442, but not with the 2501, SAC, 1132 or other such features.

There are a few peripherals which attach without these connectors, because they instead have SMS era paddle cards that plug into card sockets in a special location. The devices that can plug in with SMS paddle cards are the 1053 console printer, the 1055 paper tape punch, the 1134 paper tape reader, and the 1627 plotter. All 1130 systems have the console printer (1053) configured. 

MORE INFERENCE CAN BE GLEANED FROM SMS PADDLE CARD CONNECTIONS

When I am back in the shop, I will look at the SMS Paddle Card location to see if there are sockets in place for the 1055, 1134, or 1627. I suspect not, but will have to check to be sure.

CAN ALSO VERIFY BY INSTALLED CARDS IN KEY LOCATIONS

Each device supported has a set of controller cards plugged into locations in the SLT card compartments. By looking for the presence or absence of those cards, I can double check whether the support is included for 1231, 2501, 1134, 1055, and 1627. This too requires me to physically inspect the machine during my next visit.

NEW FUSES AT CORRECT AMPERAGE

The fuses that protect the 24VAC power sequencing circuit and that protect the lighting circuit power supply were much too large or missing when I received the system. It is important that the fuse be brought down to the proper maximum as a means of protecting precious vintage components in case something fails. 

I have purchased a 1 amp FNM-1 and a quarter amp FNM-1/4 to put into fuse holders F5 and F7. When they arrive the entire machine will have its correct fuses installed and I will have repaired all the AC wiring mistakes. 

Prepared diagrams to rewire the AC terminal strips of the IBM 1130 I am restoring

MODIFIED THE ALD DIAGRAMS TO MATCH THE MACHINE CONFIGURATION

Once I realized that I would need to verify every single connection on the two AC terminal blocks (TB-1 on the rear of the power sequencing box and TB-2 inside it), I needed an easier to read diagram so that I could take off all the wires, locate the remote end of each and beep out which wire was connected to that end. 

The existing ALD page covers TB-1, TB-2 and other wiring all on one page. Further, it contains all possible wire connections although this 1130 doesn't make use of them. That complicates the diagram. I chose to snapshot the page, import the image into the Paint program and to erase all the lines that do NOT exist on this system.

PRINTED WITH MAGNIFICATION TO EASE THE WORK WHILE LAYING ON GROUND

I grabbed just the section of the page that covered TB-1 and its destinations, removed unused lines and magnified this to fill one printed page. I did a similar thing for the section that covered TB2 and its destinations. 

NOT SURE HOW TO VERIFY THE PROPER VOLTAGE FOR THE COOLING FANS

The cooling fans for the IBM 1130 system are 115VAC units. Three are wired in parallel on each of the two logic gates, plus another sits under the regulated power supplies. These should have been wired to the terminal block that is fed by the stepdown transformer T2, lowering the 230V from the wall down to the proper voltage for the fans. 

Instead, on this system, they are hooked directly across the 230VAC line. This I think can be explained one of two ways. First, the fans might be 115V units that are being fed 230, risking overheating and failure. Second, a previous owner may have replaced all seven fans with 230V units and changed the wiring to match.

The problem with the second possibility is that it locks this system to 230V line power. The design scheme that uses 115V fans allows the machine to be hooked to 115, 208 or 230V. Transformer T2 handles the two higher voltages, otherwise the transformer is eliminated from the machine. I suppose that I could reverse wire the transformer in a 115V situation so that it stepped up to 230V for the fans, but this is counter to the design of the system. 

MUST WAIT ON REPLACEMENT TRANSISTORS BEFORE POWERING UP THE 1130

With two of the six transistors missing in the +6V supply, it would be too risky to attempt to run the machine as it is. There is some margin between the actual draw of the machine, as configured, and the 24A capacity of the supply. However, the capacity is down to 16A because of the missing transistors. 

I have replacements on order from two sellers on eBay. One is stateside and the other is in Germany. In spite of the estimated delivery dates on the site, neither has actually been handed over to the postal authorities yet. Thus, I have little confidence in the projected date until they are truly in the mail. Best case I will have them installed by the end of this week coming up. 

Identified bad power transistors, determined AC wiring of the IBM 1130 is scrambled and needs rewiring

CONTINUED REPAIR OF +6V POWER SUPPLY

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VALIDATE EACH TRANSISTOR INDIVIDUALLY BEFORE FINAL TEST

Having disconnected the chained wiring (buses) that hooked the six heat sinks together, I can put transistors in one sink and wire it to the power supply chassis, then test it individually. Each of the transistors is designed to handle 4A of draw at the target 6V, in parallel the six handle the full 24A that this supply is designed to provide.

Germanium transistors are tricky to test with a VOM but I suspected that two of them were defective. To be sure that the four I believed sound were in fact able to handle the workload, I tested them individually with a single heat sink wired in. 

My bench supply can only deliver 5A of DC to the supply I am testing, but that is perfectly adequate to load down one transistor with its rated 4A. I verified that the supply was consuming reasonable power and producing a very stead 6V output as the load was added and removed. 

Load testing one transistor at a time

I then swapped in the other three transistors I believed were good, one by one, and they too held up well providing 4A of regulated 6V supply. Once my replacement IBM 108 transistors arrive and I test them too, I can put the entire chain of six heat sinks together to form the full 24A supply. It will be at that point that I use my complex of resistors to draw the full load. 

Of course, I can't feed it with my bench supply, so I will take advantage of the unregulated 8-9 VDC from the IBM 1130 but leave the output of the supply connected only to my resistor complex. That final test will verify that the supply is fit to be put back into service in the machine.

MORE TESTING OF THE AC WIRING AND MORE ERRORS DISCOVERED

Previously I have found that the cooling fans in the logic gates and power supplies come on with the 230V main contactor, not through the 115V stepdown transformer as they should. I also found that the lighting circuit power supply is connected through the convenience outlet circuit and not through its own fuse.

As I began stepping through the two major AC terminal blocks, TB1 and TB2, I came across the next mismatch. This system is wired for a 1442 card reader/punch, which has a convenience outlet that is fed at the same time as the outlet on the side of the processor. The wire marked hot is connected to the terminal block assigned to neutral, and vice versa. 

Now this by itself isn't a huge issue, since with a transformer generated 115VAC there is no obvious side to be neutral versus hot. However, having the outlet on one machine conflict with the outlet on the other, opens the risk that two devices plugged in, perhaps oscilloscopes, will have 115V across the respective neutrals. Some old devices tied neutral to the chassis, so this opens up risk of electrical shock.

However, even if it were totally free of consequences, miswiring like this indicates a troubling history for this machine and I believe it needs to be restored to its canonical wiring. 

PLAN TO REWIRE THE AC TERMINAL STRIPS TO RESTORE TO IBM DESIGN

Therefore, I am going to take all the wires off the terminals, beep out the remote ends, and connect them according to the wiring diagram (and IBMs design). The last restorer has shared that he receive it in this condition and has been worried about deviant AC wiring routes. 

Working on power supply, discovering more issues with the power system of the IBM 1130

APPEARS THE POWER SUPPLY ISSUE IS NOT A WEAK CIRCUIT BREAKER

I had reset the circuit breaker and powered up the IBM 1130 to see if it ran for a bit and turned off, but it tripped immediately. Pulling the supply out and over to the workbench, I fed it power and applied a modest load. It immediately collapsed, the symptom being a dramatic drop in output voltage with a large demand for current. 

My power supply could only deliver 5A to the power supply thus I can only ask my electronic load to pull about 5A before my bench supply becomes the limiting factor. That was not enough to pop the circuit breaker, but it did hold for the 5A being consumed. 

If the output voltage had remained at +6 I would suspect the breaker couldn't handle greater than 5 but less than 24 amps, but the sag tells me the supply itself is faulty. I will turn my attention there.

This supply takes unregulated DC, 8 to 9 volts, with an unusual connection topology. The minus side of the raw DC is connected to the input of this power supply while the plus side of the raw DC is hooked to the regulated 6V output side! The supply works by floating the common (ground) side of the supply output to maintain 6V between common and output terminals. 

It is much more typical to have the minus side of the raw DC tied to the common output, with the plus side as an input.  This makes it very difficult to take a modern power supply and installing it as a substitute. When I hooked up a modern buck/boost unit this way it passed the full raw DC voltage to the output terminals. Not a good situation. 

BENCHWORK ON THE +6V POWER SUPPLY (REGULATOR)

I took apart the power supply and removed the six Motorola 108 transistors that comprise the output section. These are PNP Germanium power transistors thus they don't provide easy evidence of failure with a VOM, unlike Silicon transistors. The only good method would be to use a transistor curve tracer. 

The supply uses six aluminum heat sinks, each with a model 108 installed, wired in parallel. The bases are all tied together, same with the collectors. The emitters have a 0.1 ohm resistor connected to a common bus across all the transistors. The six heat sinks are electrically connected to the collectors of the transistors and aluminum bars connect them together. 

After unscrewing the connections, the six heat sinks are separated thus the collectors are not tied together but the base and emitter buses are hooked together with wires. Because of this, I can determine which transistor(s) are not working properly and replace them, because I can connect one collector at a time. 

I unwired them and now have six separated heat sinks with the transistors removed. I can install one transistor at a time in a single heat sink and test them. The supply is rated at 24A, thus each transistor is rated for 4A capacity. I can easily drive this level with my bench supply and electronic load.

PREPARING TO LOAD TEST THE SUPPLY WHEN NEW TRANSISTORS INSTALLED

In addition to testing out each transistor individually as described above, I want to load test the entire power supply after it is repaired but before it goes back into the IBM 1130. To do that I need to sink 24A at 6V, dissipating 144 watts of energy. A resistor to handle that would be 0.25 ohms but it is not reasonable to buy one that can handle 144 watts or more. Instead, I will use parallel resistors to divide the load and allow the use of modest sized resistors.

I chose to use 16 10W ceramic resistors of 1 ohm value. I will wire pairs together in series to form 2 ohm units that handle 20W. These pairs can be wired together in parallel, with eight pairs giving me 160W capacity at 1/4 ohm. I can start with two pairs, then four pairs, six pairs and finally all eight. That will let me start with a 6A load, building up in steps of 6A additional until I reach full capacity at 24A. 

AC WIRING IS SCRAMBLED IN THE IBM 1130 I AM RESTORING - UNFORTUNATE'

I was investigating the lack of 7.25VAC lighting power in the system, tracing all the wires and checking for voltage at various points. This power supply is fed by fuse F7 which should be a 1A cartridge. The fuse holder was empty, but I put in a cartridge to test. 

To understand what follows, keep in mind I was carefully staging my tests, section by section, inserting fuses only when I tested that portion of the machine. Thus, this test was done with only two fuses inserted - F5 to provide the 24VAC that sequences power-up and F7 to deliver 115VAC to the lighting power supply.

I worked with the wiring diagrams and beeped out each connection in order to find the fault. When I beeped back from the lighting power supply transformer to the SAC power distribution terminal block, I found the wire was hooked to the wrong place!

Instead of taking power from the output of fuse F7, it was tied to the convenience outlet fuses. Thus it would have had power if all the fuses were installed but I caught it because I isolated sections in my testing. The worst part of this is the lack of protection from overload this causes. The convenience outlet fuse is 6 1/4 A but the lighting supply should be protected with a 1 A fuse. 

I had previously found the cooling fans turning on when they shouldn't, going directly to the 230V supply instead of coming off the 115V stepdown transformer. I still don't know if the fans were replaced with 230V blowers or they are just running on borrowed time at twice the rated voltage.

Still, with two wiring deviations discovered already I think I need to go back to square one and validate every link. I want this put back to the correct wiring before I proceed further. Good power is everything when you deal with a vintage system. 

Preemptive purchases to continue repair of IBM 1130 +6V supply

FOUND AND PURCHASED SOME ORIGINAL 108 TRANSISTORS FROM EBAY

Two different providers had multiple of the Motorola manufactured 108 transistors. These are high current Germanium PNP transistors that IBM used in all of their SMS and many of their SLT power supplies. One of the suppliers could deliver four in just a few days, which should be sufficient to handle any failed transistors in the +6V supply. 

CIRCUIT BREAKER ORDERED JUST IN CASE IT NEEDS REPLACEMENT

I found a small breaker that I can wire in to the supply replacing the existing switch type breaker, in case the breaker itself is the issue causing the supply to trip out. I should have it by the weekend.

Power testing on IBM 1130 System under restoration, part 2

REPLACED ORIGINAL RELAY IN VOLTAGE TEST BOARD

I had mentioned previously that the voltage testing SMS card had one of its relays removed and replaced with some IC-like substitute. I found the original reed relay in the parts box, tested it and found it worked just fine. I removed the substitute and put back the original on the board. No idea why it was changed, although it was the one to validate +6V, the same rail whose regulator had failed. 

REPAIRING THE 6V REGULATOR

I didn't have a bench supply able to delivery more than 20A of 6V power. The unit installed in the machine as a substitute, a $12 part, wasn't going to be used if I could help it. I pulled the regulator and began to trouble shoot the unit.

This supply uses a set of six power transistors in parallel to handle the +6V current. One of them was dead shorted and causing the regulator to pop its breaker. I removed that one transistor, leaving five that could handle 21A out of the 24A original capacity. This is a short term situation while I acquire a replacement transistor to mount in the supply. 

I set up the supply on the bench, fed it with 9V power and set its output to 6V. I hooked up my electronic load, which is only able to sink up to 5A of current. I don't have large resistors or other means of driving the supply beyond this level, but it did perform well and stay right on voltage through that level of load.

I had to verify all the wiring surrounding the 6V supply. The terminal block was missing a couple of metal bridges that tie pairs of terminals together, pretty critical to the operation of the regulator. With all of them in place, the other ends of all the wires verified, and the regulator back in the machine, I was ready to adjust all the rail voltages.

CHECK REGULATED DC VOLTAGES

With all the raw DC and AC power looking good, it was time to validate the controlled voltages for the SLT logic produced by three regulators. I switched on CBs for +6V, +3V and -3V one by one. After powering up, I checked the levels at the wiring going to the rail connectors on the main logic gates. I was tweaked all of them to the middle of the valid ranges. 

With this done, the next step was to connect the power to the logic circuitry and power up to begin the debugging. I still have an issue with the 7.25VAC supply for the panel lights, but the rest of the machine is good as far as power.

I powered up the system, which then lit the RUN lamp indicating it is executing some code. I flipped the rotary mode switch to Single Step (SS) which extinguished the light as it should. Once I have the lights working I can check to see why the RUN condition is active. There are two relatively innocuous reasons - a hot interrupt or a hot cycle steal (DMA access) request from a peripheral device that is not currently connected. Other defects could cause this too. 

BREAKER TRIPPED AGAIN ON THE +6V REGULATOR

The regulator tripped causing the machine to power down exactly per its design. There are two possibilities here - the breaker may be weak or the regulator may have additional power transistors failing. The breakers on similar supplies used on the IBM 1401 systems do sometimes start tripping well below their target current level, requiring replacement with a proper breaker. 

I can quickly determine whether we had a new transistor failure by resetting the breaker and powering up again. If the system comes up for a short time, then the issue is the breaker. If it trips immediately, we have more repair to do on the regulator itself.

BEGINNING TO INVESTIGATE THE LACK OF PANEL LIGHTING POWER

I put in fuse F7 for the panel lighting power supply, then checked the AC inputs to the supply which should have 115V present. The lines were not energized. I began testing continuity of the wiring back to the sequencing power box which houses the fuses. I ended for the day before I completed this, but with the problem sitting on the AC input side, I am confident I will have this back in operation shortly.

Power tests of the IBM 1130 system under restoration - part 1

REMOVING FUSES, DISCONNECTING TRANSFORMER OUTPUT AND OPENING BREAKERS

In order to carefully step through the checkout stage by stage, I had to disconnect various parts of the power circuitry. There are seven fuses which control power to various power supplies, convenience outlets and the power sequencing transformer that is essential to turn on an 1130.

Each of the voltage regulators has a circuit breaker, which I opened to block them from energizing logic circuits throughout the machine. The +6V substitute regulator does not have a breaker; I disconnected its input instead. 

There are two transformers which were substituted by a prior restorer. One of them is connected only to the convenience outlet inside the machine and its inputs are connected through a fuse. The other, however, is directly connected to input power when the main contactor energizes when the power switch is thrown. It powers various fans throughout the machine which I don't want energized initially, so I have to pull the wires off the secondary to block that transformer. 

With all these disconnections and fuse removals, the machine should not provide power to anything besides the power sequence logic itself. I can then insert fuses, connect wires or switch on breakers selectively to test section by section.

VERIFY ABSENCE OF POWER THEN CHECK 24VAC POWER SEQUENCING VOLTAGE

With the plug inserted into the 240V outlet, no fans should run, the unit should not power on and I shouldn't find AC anywhere outside of the power sequencing box. I verified that this is true. 

Next, I inserted fuse F5 which provides power to the 24VAC transformer. I could see the 24V appear on the sequencing lines and the relay R3 energized which among other things allows AC to flow from transformer T3 to the convenience outlet. 

VERIFY SUBSTITUTE TRANSFORMERS DELIVER 120V

Inserting fuses F3 and F4, while F5 was still in place, energized transformer T3. I checked the voltage at the convenience outlet which was indeed 120V as intended. This gave me some confidence but I still will check the output of transformer T2 to ensure it too is delivering the proper voltage. To test this I had to switch on the power switch of the 1130 system, causing the contactor to energize. 

This was a good time to verify that all the fans began spinning around the machine. However, they were spinning without T2 connected, thus they are wired in some nonstandard way.

ANOMALOUS WIRING AND COMPONENTS DISCOVERED

The fans should be 115V blower motors whose power is fed from the stepdown transformer T2. This allows machines to be used with 115, 208 and 230 volts, the transformer converting the higher voltages down to 115 as a standard input to motors, fans and power supplies.

However, they are spinning when the only power present is 230V. I see they are wired in odd locations on the terminal bus, which is how they get power early, but I am waiting to hear from the prior installer to learn whether these are 230V substitutions or something else was done to make them run. 

When I was checking all the power sequence wiring I came across a replaced relay. Instead of the small relay used on the SMS card for power level checking, a large IC style component was soldered in place. As long as this switches on when the voltage rail is active and switches off when the rail drops, the substitute is okay to keep.

I did look at the specifications of the power regulator for the +6V rail, since a modern substitution was put in place. The regulator used by IBM can deliver up to 24A at 6V, while the modern part has a capacity of 10A on paper and probably less without serious cooling. Even if it provides noise free and stable power at 6V, it lacks an overvoltage protection which is an important feature of the IBM supplies. 

I am not happy with the 6V regulator in the system and will have to address this. Long term, I will repair the IBM regulator and put it back into service, but in the short term I will look for a different high current regulator with overvoltage protection. 

CHECK RAW DC AND AC POWER LEVELS

I hooked up the output of T2 to the power circuitry and once again switched on the 1130 system. The contactor engaged but with fuses F1, F2, F6 and F7 out, there should have been no power to the power supplies. I checked and this is true.

Next, I inserted the fuses one at a time, checking the output of the power supply it energized. F1 provides power for the raw voltages that produce the +3, -3 and +6V. F2 provides power for the 12V and 48V DC supplies for core and relays. F7 energizes the 7.25VAC power for lighting circuits. F6 is power to the various peripheral devices, which I verified at the power connectors for those devices. 

The fuse for the lighting supply was missing from the holder. When I put one in, I did not see the 7.25V appear at the lighting PCB. I will need to track this down and figure out what is happening, then repair it.