A friend of mine has an old video game system called Vectrex that hasn't been working lately and I told him I'd see if I can figure out what the problem is and fix it.
I think I've narrowed it down to a power supply problem. When I had it open and was checking various points with the scope, it turned on a couple of times but most of the time it wouldn't. I found that when it wasn't working, both the input and output of the LM340 positive voltage regulator were around 1-1.2V. It should be 9V in and 5V out. The times it turned on correctly verified this.
So my initial thought was a bad regulator, but I want to make sure before I go desoldering things. I'm unsure because the while the 5V regulator output goes to power the logic board, the 9V input is branched off to power things like audio opamp, video circuit and CRT. I don't know if something down that 9V path might be the problem.
The power board schematic is on page 32 of this manual:
http://www.vectrex.biz/Vectrex_service_manual.pdf
What do you think? Should I try replacing the regulator?
I think I've narrowed it down to a power supply problem. When I had it open and was checking various points with the scope, it turned on a couple of times but most of the time it wouldn't. I found that when it wasn't working, both the input and output of the LM340 positive voltage regulator were around 1-1.2V. It should be 9V in and 5V out. The times it turned on correctly verified this.
So my initial thought was a bad regulator, but I want to make sure before I go desoldering things. I'm unsure because the while the 5V regulator output goes to power the logic board, the 9V input is branched off to power things like audio opamp, video circuit and CRT. I don't know if something down that 9V path might be the problem.
The power board schematic is on page 32 of this manual:
http://www.vectrex.biz/Vectrex_service_manual.pdf
What do you think? Should I try replacing the regulator?