Repair Update
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by Bill Degnan - 07/09/2022 20:20 |
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Bob Grieb took a stab at the repairs of this terminal. First he used the technical documentation he has to ID the correct power supply component. He found a replacement for sale and ordered it.
The machine has power again. "I cut new rubber washers for the keyboard (75 of them) out of a tractor tire inner tube. Today the assortment of reed switches arrived from Digikey. They are really cheap, so I bought 3 kinds, 5 each. The magnetic field strength required to close the switch was different for the three types, since I didn't know what part was originally used. One of the three seemed fairly close to the old switches, so I installed four of them to replace ones that were broken. The power cord arrived today. The connectors used for the 5 pc boards require an uncomfortable amount of force to plug them in. Hope I didn't break anything. I don't like pushing that hard on anything that old... I have not applied full line voltage to the power supply yet. Will probably do that tomorrow." --- I figured out how the CRT got the burn mark in the very center. When you turn off the terminal, the deflection stops right away, but the beam is still on, so it's very bright right in the center. Over time that burnt the phosphor. I will see if turning down the intensity first prevents that. If I press a key, it repeats until I hit Rub Out or Backspace, or a few others. Unfortunately, I am currently thinking this is not a problem with the keyboard, but rather with the screen buffer control circuitry. But I am not sure. When I first powered it up, the intensity control was not set to show a beam. I played with it a little. Turned it back and forth to clean it, as it's a sealed pot. Anyway, I have not noticed the issue you mentioned about characters not being visible sometimes. More testing needed. The G and J characters were repeats when I pressed those keys. ------------ No characters are currently being sent to the screen. Continuous characters are being transmitted from the serial port. ----- Fixed the repeating character issue. I was able to power up the Interface 1 board by itself, and found a couple of bad 7474 chips. Luckily I had two of them from a long time ago. Reply |
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