TRS-80 Model 100 is frozen, even after multiple resets

Question

I replaced all leaking capacitors about 4 months ago. I cleaned it out the board tediously.

Every-time I switch on my old computer it is stuck on the menu screen. The machine does not respond to the keys I press. Even the clock is frozen on the screen.

Holding done CTRL, Break and Reset 20 times does nothing to break out of the freeze state. Turning off the memory switch doesn't work either. It was working fine for 4 months.

Question

How do I break out of these lock ups? What's the likely culprit to the lockups?

Linked to troubleshoot pdf

Answer 1

1. does the board have any sockets for ICs ?

   if yes remove all chips and pull them back (not all at once do it one by one) sometimes the pins oxidize and or get out of the socket a bit making bigger resistance and noisy buses creating havoc usually ending up with freeze or reset or gfx errors. Be careful not to bend and or broke the pins and use the same IC orientation sometimes cleaning with alcohol helps (using tooth brush but do not push too hard).

   the same goes for any connectors (like connection between more PCBs)

2. did you replace all capacitors in the correct position?

   if you swap +/- pins the cap will diminish its capacity or leak or blow much faster than it should so check all replaced caps.

   if you use tantals make sure they can be used in such way (some blocking and filtration caps need to be a specific technology and not interchangeable) and also have correct orientation. These suckers either blow but more likely generate weird voltage offsets (even several volts) where they should not and are causing electrical havoc in all interconnected circuitry which might help to blown other caps and or even ICs ...