Watched pot syndrome - can't get the 1130 6V power regulator to trip now that it is instrumented

REMINDER OF THE 6V REGULATOR ISSUE

The 1130 logic rails are +3V, +6V and -3V in addition to some special voltages for other purposes. DC is produced in a power supply unit and fed to voltage regulators that produce the three logic voltages. The regulator for +6V is where the issues arise. A circuit breaker on the regulator will trip if the current demand is too high; in addition it will trip if the output exceeds a voltage threshold and triggers an overvoltage clamp. 

If the 1130 has been previously powered up but is turned off for a relatively short period, when it is turned on again, the circuit breaker would trip. I monitored the current being demanded through the regulator and found that it did NOT go to high levels when the problem occurs. I verified that the overvoltage clamp card was not firing. 

When I watched the output voltage, I would see 6V during normal operation but when the circuit breaker trips, the output was around 3V and I could see it oscillating a relatively small amount around that average. 

I replaced all the resistors on the regulator control card and tested some of the transistors on my curve tracer to see if I could find a semiconductor that would fail if it was hot from prior operation. I didn't find anything suspicious. 

INSTRUMENTED FOUR SPOTS ON THE REGULATOR CARD

Circles around four wire taps

I soldered wires to four spots on the regulator card, in order to have four traces recorded on my oscilloscope. I wanted to see how the circuit behavior changed when it went to the 3V oscillation before tripping the circuit breaker. 

MANY POWER CYCLES ATTEMPTED WITH NO ISSUES ENCOUNTERED

I hooked up the scope and powered up the 1130. I then tried for an hour to run it for various lengths of time, power down for a short while and bring it up again. It NEVER tripped the CB nor dropped the output voltage to 3V as it had been. Everything I tried failed. 

This is an example of the watched pot that never boils. At this point I have to assume that something I did while tacking on the four wires to the regulator board is the reason that it no longer failing. That might be a cold solder joint or a cracked trace. I will have to examine the board very very closely at the four points where I added the wires.