Sunday, April 17, 2022

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. 

2 comments:

  1. Wouldn’t you love to have the pedigree of this machine, so you would know who made all the modifications, and why? These were not just a couple of trivial changes.

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    1. I would but I don't want to do anything to upset the people for whom I am restoring the machine. Even if I knew I would have to be circumspect about the machine.

      I am fairly sure this happened before the current owners had the machine. The last restorer has mentioned to me that he was quite concerned about the state of the AC wiring.

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