Discovered fault in 6V Power Supply, system powers up; beginning of logic debug

INVESTIGATING NON-ISOLATION OF DC SUPPLY 16.5 OUTPUT

The DC Supply 16.5V (nominal 12V) output should be fully isolated from any other circuit in the machine. It is produced by separate secondary windings on a power transformer, not tied to neutral, ground or any other wire. 

Bottom section (12v at 24A) is the 16.5V supply for +6V

As you can see from the diagram above, the raw DC that is hooked to the +6V Regulating Supply should be fully isolated. As such, adding one connection to the Regulating Supply cannot create a circuit and current flow with this. I did see 10V between the common output wire and the common output of the Regulator Supply, which definitely explains the flow of current and breaker triggering.

Regulating supply with 16.5 in, common wire connected only

It was time to look for sneak paths, miswired connections or component failures that might connect something in the DC Power Supply 12v at 24A section with any other wire in the 1130 such that it causes the symptoms I am experiencing.

The problem was indeed a sneak path, but not in the DC Power Supply. I had slid the +6V Regulating Supply into its mounting rails for my tests, but hadn't tightened the bolts that hold it in place. As a consequence, it sagged a bit and unbeknownst to me the heat sinks of the supply were contacting chassis ground! 

CORRECTED PROBLEM, VERIFIED ISOLATION,TESTED WITH ONLY COMMON TERMINAL 

I held it in place and tightened up the mounting bolts. These are accessible from deep inside the rear of the machine after swinging the logic gates out, just to explain why I didn't take that step initially when I was putting the supply in and out of the machine. 

The problem was gone! Time to hook up the common output lead and power up. That also worked fine, no tripping of the breaker and a solid 6V across the outputs. 

TESTING SUPPLY WITH BOTH WIRES CONNECTED, ADJUSTED 6V RAIL LEVEL

Turning on only the 6V Regulating Supply circuit breaker, but not the +3 and -3 supplies, makes it safe to energize for a brief period while I adjust the regulator potentiometer to get the +6V rail spot on its target voltage. I did set it as close to 6.00 as possible. To be extra careful, I went back and tweaked the other supply voltages to 3.00 and -3.00 as close as I could. 

BRINGING UP ALL POWER TO THE 1130

I flipped on all three circuit breakers for the logic rails, made sure the fuses were in place for all DC voltages (-3, +3, +6, +12 and +48), then switched on the processor. It came up, lights were displayed on the console panel, and I saw signs of life.

INITIAL OBSERVATIONS

The RUN lamp goes on immediately when the system is in Run mode, but putting it in single step (SS) mode kept it stopped. I suspect I may have a hot cycle steal that is forcing this to run, however other issues can cause this as well.

The console entry switches were set and indeed their values are gated into the IAR register while in Load mode. The Prog Stop button triggers interrupt level 5 just as it should. 

Of the CE controls, I found that Lamp Test worked but Storage Display did not, largely due to the machine being in a run state. There was no parity error indicated for the initial location (x0000) which suggests that at least that location of core memory is working properly. 

I smelled some smoke and found the CE Meter power box emitting wisps of smoke. I will have to check into that and figure out what is going wrong there. Fortunately this is not a mission critical function and to boot it is relatively easy to fix.