Finished AC rewiring, had an issue with the console light power supply that needed addressing

COMPLETED TB-1 WIRING WITH MODIFICATION

I implemented the split where the fans are grouped on the 230V line, jumpered over to the section of the terminal block for 230V, while the 115V output of T2 is reserved for the 1053 typewriter motor. Or so I thought - more later. 

COMPLETED TB-2 WIRING

Similarly, I finished putting the TB-2 wiring inside the power distribution box back to its original layout. This involved tracing every wire with the continuity checker to be sure that they were all in their correct places. 

DISCOVERED THAT THE DISPLAY PANEL LIGHTING POWER SUPPLY IS 115VAC

Having restored the wiring for the 7.25VAC power supply to the circuit fed by fuse F7 and having a suitable low current fuse in place, I turned on the machine to verify the lighting voltage was present. Nothing. In fact, the fuse blew!

I looked at the diagrams to see if this was wired improperly or was set up for 230V. That is when I noticed that IBM didn't provide the ability to switch the supply between 115V and the higher voltages. Instead, they ship either a 115V supply or a 208/230V supply. Reading the part number quickly confirmed that it was the low voltage version. 

IT APPEARS THIS MACHINE WAS ORIGINALLY CONFIGURED AS A 115V SYSTEM

This explains a lot. No wonder I didn't find the Ferro Resonant transformers used by IBM, instead finding some low capacity alternatives in place. When a machine is ordered for 115V, IBM does not include the transformers as there would be no need to step down voltage. 

A prior restorer converted this to 230V, adding the transformers and swapping all the fans to 230V versions. That left the AC wiring inconsistent with the wiring diagrams and usual IBM practice.

MODIFYING THE TB-2 AREA TO SUPPORT THE LIGHTING SUPPLY

Since transformer T2, normally providing power to fans as well as the 1053, is underutilized right now, I found a scheme that would let me move the lighting power supply over to the 115VAC fed by T2. This involved adding a metal jumper and moving a couple of wires around on TB-2. 

Rewiring of transformers completed, rewiring of all AC connections underway, load tester prepared, blower voltage verified

ROMEX REMOVED AND IBM STYLE WIRING INSTALLED FOR THE TRANSFORMERS

As I mentioned previously, the use of ROMEX style wiring is inconsistent with the wiring methods used in IBM mainframes in the 1950s, 1960s and 1970s. I decided to rewire with 12 gauge stranded single wires, wrapping them together with lacing much as IBM did during manufacturing.

Rewiring the transformers and lacing the wiring bundle

REWIRING BOTH TERMINAL BLOCKS THAT HANDLE AC POWER CONNECTIONS

I have disconnected all the wires and am proceeding slowly and carefully reconnecting these in accordance with the original design. This will return the machine to the condition it would have had upon installation in the customer's location.

TB-1 on rear of power distribution box

TB-2 inside power distribution box

LOAD TESTER FINISHED AND READY WHEN THE POWER SUPPLY IS REPAIRED

I completed all the cabling to produce my resistor complex to load down the 6V power supply for its final testing. This design has four segments, each draws 6A and they can be connected in parallel to draw 6, 12, 18 or 24A. 

Each black lead adds a 6A load across the two long wires

REMOVED AND VERIFIED VOLTAGE OF BLOWERS IN THE MACHINE

The fan assembly underneath the midpack voltage regulators was easily removable, which allowed me to see the dataplate on the fan motor and verify exactly what voltage these operate at. It is 230VAC. 

IBM fan was replaced with a 230V version

Removing fan assembly from under midpack regulators

IBM thoughtfully designed the 1130 so that it could be connected to three different mains voltages - 208, 230 and 115. Most of the transformers inside power supplies had multiple taps, selected by moving wires and connecting jumpers to configure for the appropriate voltage. 

There were a few items that were 115VAC only, due to limitations of the components themselves or to simplify IBM's supply chain. The fans that cooled the system were 115VAC, thus a stepdown transformer was included for any system that hooked to 208 or 230 mains supply. The motor in the selectric typewriter based 1053 Console Printer ran on 115VAC. 

Finally, to standardize the tools that IBM deployed throughout their organization, all tools were 115V. To support use of these tools, IBM had convenience outlets inside most of their machines which let the field engineers plug in their tools regardless of the voltage levels used by the rest of the machine. A stepdown transformer produced the 115VAC for convenience outlets.

This machine had the original IBM fans removed and new blowers installed that ran on 230V, thus obviating the need for stepdown transformer T2 to produce the 115V to run cooling. However, the transformer is still used to deliver 115VAC to the 1053 printer and it supplied over the power cable to the fans on the IBM 1442 Card Reader/Punch. Fairly wasteful but this is the only way to drive the typewriter motor. 

ISSUE SPOTTED WITH THE CONVENIENCE OUTLET TRANSFORMER T3

The second stepdown transformer T3 is provided to deliver 115VAC to the standard US style duplex outlet. IBM shipped only 115V tools to its FEs, who plugged them into these convenience outlets. Thus, any machine hooked to 208 or 230V mains had to step down the voltage to support the outlet. While a single transformer could have supported the fans, the typewriter motor and the convenience outlet IBM chose to isolate these so that if the convenience outlet blew a fuse it didn't stop the fans from operating. 

While I was wiring these up and fastening them down so they didn't slide around inside the computer, I noticed that the data plate identifies the capacity of this transformer as 300VA. For a 115V convenience outlet, this allows only 2.6A of current, not the full 15A one would expect from a standard duplex outlet. IBM configured the fuses for the convenience outlet transformer at 6.25A to the primary of T3, which supports 12 1/2 A or more at the outlet. I am going to drop the fuse used for this circuit to 1 4/10 A as that will match as closely as possible to the capability of this substitute transformer. 

PLANNED TO REWIRE SLIGHTLY TO HANDLE THE 230V FANS

Because of the use of 230V fans, they must be hooked to different locations than originally designed. The factory shipped systems had six positions on the terminal block assigned to the 115V output of transformer T2. That was hooked to the fans in the logic gates, the fan circuits to peripherals such as the 1442, and to the SMS based power that feeds, among other devices, the motor of the console printer. Each set of three positions is jumpered together and hooked to one side of the T2 transformer output. 

With metal plate jumpers, we have the transformer hooked to one terminal and the other five available for fans and other power destinations. The 230V supply comes out of the power distribution box and hooks to two pairs of terminals. Each pair (7&8 or 9&10) is jumpered together. The input power to transformer T2 is fed from these terminals. They also provide power to most of the fuses on the distribution box and provide 230 to circuits for peripherals such as the 2501. 

The four terminals on each pair for 230V can't easily sustain another three connections each for the fans. Since the fans are not going to be connected to the T2 output any more, I reassigned some of the terminals on the strip. Now, terminal locations 1 and 2 will be jumpered by wire over to the 230V on 7&8, while terminal locations 5 and 6 will be wire jumpered to terminals 9&10. I removed the metal plates bonding these to terminal locations 3 and 4, which remain assigned to the 115V output of T2. 

Terminals 3 and 4 carry the 115V to the SMS connector for the 1053 Console Printer motor, as well as to the fan power pin for the 1442 Card Reader/Punch. 

Jumpers to bring 230V over to the fan screws on terminal block

While this sounds simple to execute, the challenge is that IBM's cables are carefully cut to length and laced together so that each wire end naturally reaches its destination terminal on the block. Because I have moved some things around slightly the wires don't fit so naturally to their new destinations. 

Short work session, finalized configuration check, unwired AC terminal block and put together resistors for load testing

SHORT SESSION TODAY

Today is the due date for filing individual income taxes in the US. I had prepared the taxes a few days ahead - it was pretty complex with the move between states, sale of the house and other events - and attempted to electronically file Friday night.

The return was rejected by the IRS, claiming that another return has already been filed under my taxpayer ID number. This is probably some kind of fraud where someone filed a return asking for a refund, claiming very little income. I have to deal with this, however.

I put a freeze on my credit agency files to protect against someone using the same identity information to attempt to sign up for credit under my name. There was no recourse other than to file by mail, including an affidavit that identity fraud was involved in the 'prior filing' they mentioned. This involved printing scores of pages of forms, signing and putting it all in a large envelope. 

The state return to California also had to be filed by mail. This was even more pages printed, both the CA forms and a copy of my federal filing, in its own large envelope. For reasons too arcane to cover here, California won't accept a check from me thus I also had to send an electronic payment to match the amount due. 

This morning we had to visit the post office, ensure the postage was correct and mail it off on the due date. From there, our overly shaggy dog had an appointment for grooming that extended into the mid afternoon. 

CHECKING THE PRESUMED CONFIGURATION BY LOOKING AT SMS PADDLE BOARD

The 1130 has a small metal plate that holds SMS sockets where various peripherals are connected via SMS paddle boards. The first two positions on the plate are assigned to the 1053 console printer, the remainder are used for the 1134 paper tape reader, the 1055 paper tape punch and the 1627 plotter. There were no sockets or wires except for the first two positions, which proves that this machine did not have 1134, 1055 or 1627 attached.

CHECKING PRESUMED CONFIGURATION BY LOOKING FOR ASSOCIATED SLT CARDS

I swung out gate A and opened compartment A1 to check for the cards that are associated with the 1231 Optical Mark Reader. On my own machine, these card positions are empty but on the 1130 I am restoring the cards are all in place for the 1231 controller logic. 

With all these checks, I can now confirm that this is an IBM 1130 model 2B, 8K core at 3.6us memory cycle time, featuring the 1053 printer and keyboard, the 1442 reader/punch and a 1231 optical mark reader. It had no other peripherals attached or configured into the system. 

BUILDING RESISTOR COMPLEX TO LOAD THE POWER SUPPLY

I soldered together the 1 ohm 10W ceramic resistors I bought to form 1 ohm blocks that can handle 40W of load - two resistors in series, plus another two in series, both pairs hooked in parallel. These four 1 ohm blocks are mounted on terminal blocks so that I can wire them up with heavy gauge wire in a few different ways. 

If I hook just one set of resistors up, it draws 6A from the supply. Two sets in parallel bring the load up to 12A, three sets get me to 18A and all four together will draw the full 24A that the supply is designed to deliver.  

resistor load complex to draw 24A

I am almost done, I just need to cut and install the lengths of wire that allow me to select how many resistor sets are in circuit and that connect this load complex to the power supply.

UNWIRED THE AC TERMINAL BLOCK IN THE POWER DISTRIBUTION BOX

The terminal block TB-2 inside the power distribution box connects various fuses and power lines to destinations throughout the machine. Since I found several connections to be incorrect, I decided the best course was to detach all the wires, beep out the other end of each and then place them back on the proper location on the terminal block. 

I had previously verified that positions 1 and 2 were properly wired, but encountered errors when I hit 3-4 and 5-6. I left the first two connected. These hook the fuses F1 and F2 to the raw DC power supply inputs. One of the inputs produces the +6, +3 and -3 supply raw power (the 6V raw power is close to 8V coming from this supply but is regulated down to +6V in the power supply I am repairing). The other input produces the +12 and +48V power which is used for functions such as driving relay coils. 

All the other connections were removed from the terminal block strip and the screws placed in a plastic box. The next time I go to the shop I will find the proper wires by beeping and screw them down where they belong. When this is done, I still have to fix up the TB-1 terminal block that sits outside this box on the rear. 

REPLACING ROMEX CABLE WITH MORE TYPICAL STRANDED WIRE

The two transformers that were replaced in this machine by a previous owner are both stepdown from the 230V supplied from the wall to 115VAC for various purposes. One of them supplies the convenience outlets on the 1130 and attached peripherals. The other supplies 115V for fans and other elements that require this voltage. 

These substitutes were wired into the TB-1 and TB-2 terminal blocks using ROMEX cable, stiff solid conductor wires in a plastic sheath. This is the wire that is used inside walls in homes to distribute power to outlets and switches. 

out of place Romex cable

Inside the IBM mainframes, however, they didn't use solid conductor wire for power, the always used stranded wire covered in plastic. The 1130 has all of these individual stranded conductor wires laced into bunches that are routed like cables throughout the machine.

I am removing the romex and installing some stranded conductor wires that are similar to the ones used by IBM. This will make the machine look more consistent with the way it was originally constructed. 

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

xxx

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.