Today I replaced all the power transistors in the 30V, 7A power supply for the 1406 box that hosts the additional 12K core locations. When they were all in place, I tested my two rebuilt voltage regulator cards. Both worked, allowing me to set the voltage and have it hold steady regardless of load or input voltage.
I moved on to the Over Voltage Protection card, which crowbars across the supply if the voltage exceeds a trigger level just a few volts above the 30-31 V normal level. The card has an SCR which shorts the output through a 4 ohm power resistor when triggered, the resulting 12A or more should trip the circuit breaker within microseconds.
Our card was quite scorched, as were the power resistors, since the circuit breaker had held open for about ten seconds, allowing almost 500W of energy to cause the resistors to glow. As the resistor is a 10W type, able to handle a few microseconds of current but not the prolonged operation during this failure.
We had a failed voltage regulator card, which let the output surge up to 40V, triggering the crowbar which did its job. The resulting 10A flow should have tripped the breaker rapidly but didn't. I found a circuit breaker on a spare power supply of a different voltage type, swapped it in and we put the repaired power supply back in the 1406 box.
The machine came up, we trimmed the voltage to spec and it performed perfectly during the public demonstration today. Pleased to get the Connecticut 1401 system back in operation after a few weeks of downtime.
IBM 1130 LIGHT PANEL UPGRADE
I am up to 24 soldered lamps on their holders, only 72 more to go for the big board. I do batches of 8 at a time, looping the bare wire ends of the lamps around the .100 spaced header pins, soldering, arranging the bulb and wires, testing on my prototype SCR circuit and then installing each into the board socket.
BUILD RELAY TESTER TOOL FOR TECHWORKS! MUSEUM IN BINGHAMTON
The 1402 Card Reader/Card Punch that is the heart of a 1401 system uses dozens of relays to sequence itself through operations such as reading, punching, run-out and initial card feed. Stan Paddock invented an Arduino based tester that drives a relay, measuring the voltage across the contacts as it operates.
We used it to shake the relay while contact cleaner was applied, then test all four or six SPDT contact sets on the relay simultaneously. It helped us identify relays that needed repair, perhaps replacement contacts or just some bending and burnishing. Without the tester it was very hard to keep the 1402s running.
To help TechWorks! get their 1402 operating, I decided to build them another relay tester based on Stan's design. It uses an Arduino, dual relay board, resistors, two DC power supplies and a pair of sockets. I have all the parts on hand, but have not yet picked out the right enclosure for the build.
Once I have the enclosure and create the mounts for the relay sockets and some indicator LEDs, I can wrie up and test the tool before shipping it to Binghamton.