Replaced two capacitors in the +3V regulator card due to high leakage

CHECKED ALL CAPACITORS FOR VALUE, SHORTS AND ESR

In order to check the capacitors, I had to lift one lead from the circuit to isolate them. I carefully unsoldered one side of each capacitor and made measurements. All of the capacitors had their rated value, a testament to the high quality parts that IBM used in their mainframes. No shorts on any of them. 

What I didn't like was the relatively low resistance of two of the 100uf capacitors on the card. While they were kind of marginal in general, I suspected that this circuit might be more sensitive to having a resistor effectively soldered in parallel to the capacitors. 

I replaced them with two new electrolytics of the same capacity and a higher voltage rating. I am not convinced that this alone was enough to repair the regulator, but it can't hurt. 

PULLED OUT IBM 028 TRANSISTOR AND CHECKED ON THE CURVE TRACER

The voltage regulator uses a cascade of transistors, each stage amplifying the current so that ultimately the regulator can drive 20A of current. The final stage consists of four 108 transistors in parallel. The stage which drives the last one has a single 108 transistor. All of those had been tested on the curve trace a few days ago and were good. 

I moved down the chain to the IBM 028 transistor which drives the single 108. That was removed from the board and the curve tracer showed that it was good as well. All the semiconductors left to check are three transistors, two IBM 026 which form a comparator between the actual voltage and the reference voltage, plus an IBM 086 that drives the 028. All the transistors are germanium; the 086 is NPN while all the others are PNP type.