Power sequencing problem found and repaired

TRACING DOWN THE FAULT IN THE POWER UP SEQUENCE

Sometimes you can test each section of a machine and find no problems, because the defect is in the interconnection. I had extensively tested the SMS sequencing card and also reverified the wiring to the SMS socket. I could observe the three primary supply rails were present at the correct voltage at the pins of the socket as well. 

Thus, it should have worked but it didn't. As I did more and more involved tests, probing parts on the board while it was in operation, I heard the relays click on and off as I applied pressure to the test point. This was the clue that led me to determine that the corrosion on the contacts of the SMS connector were introducing high resistance or causing intermittent connections. 

FIXING THE PROBLEM

Applying deoxidizing solution to the contacts and wiping them by inserting the SMS card cleaned up the contacts. The power sequencer now brings up the machine properly, delivering +12V and +48V to the machine because the main rails are working correctly. 

MACHINE NOW UP WITH LAMPS AND BUTTONS ACTIVE

When +12V is delivered to the logic gates, we will see the indicator lamps and pushbuttons that surround the keyboard on the console function as they should. The Prog Start and other buttons can be pressed and result in appropriate actions based on the rotary mode switch setting. For example, each time the machine takes a step or executes instructions, the Ready lamp will glow until the processor enters a wait state again. 

Indeed, the machine came up with a few lamps glowing. File Ready and Parity lamps were illuminated. The first is understandable since I have the drive out of the machine so that the controller logic is interpreting its state incorrectly. However, the Parity error is an issue I have to troubleshoot.

FIRST TESTS OF FUNCTIONALITY

The lamp test switch does not illuminate all the bulbs in the display pedestal as it should. The Storage Display and Storage Load switches won't cycle through memory even with the Parity Run switch set which does not set the stop latch on errors. Pushing Prog Start button does not flick the Run lamp on, although that may be a consequence of the parity error. 

Given the corrosion I detected with the power sequence connector, it is likely that I have to deoxidize all the switches before they will work correctly. I most likely have a memory related issue as well. I like to work carefully from the most central points of the machine outward, so I will begin some testing to determine how healthy the logic may be and the areas that are failing.