I've had a look at that TI-99>4A I picked up last week. As expected it fails to boot, giving a black screen with an audible tone but that's all. From what I've read on the web this is the equivalent of the dreaded "garbage screen" in other 8-bit computers and could mean anything - a faulty CPU, ROM chips, crystal , RAM (possibly) or virtually anything else supporting CPU operations. About all I know is working is the PSU and the video signal.
So, the next step would be to get the scope out, check the processor for a clock etc. and work backwards from there. I'm in two minds whether to bother though. The case is somewhat beat up...it's probably the most beat up of all the working computers I have. Also I don't have any of the major chips like the ROMS or CPU. Even if I do suspect them, I can't change them and I won't import them on the off-chance.
Reading about the computer and disassembling it has made me want to get a good working model though to add to the collection. I have some carts for it, so I've got software. The PSU works just fine as does the RF box.
Does anyone have one lying around they want to part with for a few bucks. Even if that too is battered, untested, and has no PSU, it will at least will have chips in there which might be ok and I could swap out. However, best if it's a PAL version, as the video chip differs from the more popular NTSC one (and it could be that chip).
If it is in good condition and works, even better (and I'd pay more than just a few bucks).
Anyway, PM me if you can help.