As mentioned in another thread, I have an early 800 that powers up to a solid white screen on composite and almost nil on TV.
When I first powered it up I recall having this issue. I cleaned the edges of the cards and with a bit of pressure on top managed to get the thing to power up to Memopad, BASIC, etc. I then thought I'd do a bit more cleaning of the ROM socket in particular.. after which it hasn't worked since.
When I was initially troubleshooting the first time, I ordered a spare ROM cart and plugged that in. I can no longer remember which cart it worked with, but now neither does.
I have a GQ-4x4 EPROM reader and was wondering if maybe I could read the ROMs and make sure they're still alive. I can't think of anything I might have done to damage them, apart from repeated power ups and applying pressure on the card when I was trying to get them to operate.
Other options I've considered include picking up a known good 800 motherboard, maybe another ROM cart. I'm pretty sure the RAM is good, I removed and tested with a RAM tester in an Apple II. The CPU card would be he only other unknown.
Power voltages seem to be fine. I actually went through with the ROM cart plugged in with my DMM and checked continuity between the top of each pin and where it solders into the motherboard on the other side... all seemed to make the connection (although, you can go crosseyed doing that so who knows if I missed one).
I also removed and reseated every single IC in the machine. None of the legs on them them looked dirty or rusty.
The CPU is good.. I tested it in a PET.. no problem there.
At a loss at this point.
Edited by Falter, Sat Mar 9, 2019 6:43 PM.