Okay, how much beer have you drunk?Ast A. Moore wrote: ↑Sun Jun 17, 2018 8:02 pmPin 8 is VDD, pin 16 is ground: http://pdf1.alldatasheet.com/datasheet- ... 4164B.html
Mark
Okay, how much beer have you drunk?Ast A. Moore wrote: ↑Sun Jun 17, 2018 8:02 pmPin 8 is VDD, pin 16 is ground: http://pdf1.alldatasheet.com/datasheet- ... 4164B.html
Oh, crap, it’s a bloody OR gate. I misread the number as IC22. No beer. Otherwise I’d have stayed within odd numbers. Just a long day.1024MAK wrote: ↑Sun Jun 17, 2018 11:40 pmOkay, how much beer have you drunk?Ast A. Moore wrote: ↑Sun Jun 17, 2018 8:02 pm Pin 8 is VDD, pin 16 is ground: http://pdf1.alldatasheet.com/datasheet- ... 4164B.html
You’ll need to solder a wire across these pins and then power up the machine. If you bridge them after the ROM has finished checking for the presence of upper RAM (which happens almost immediately after a reset/power on), you’ll either get no effect, or it’ll be unpredictable.
That would short the entire 5V rail of the machine. If it was brief enough, it’s not too critical for most of the components if you’re lucky (not particularly great, either), except perhaps the lower RAM ICs. Those tend to fail if one of the three power rails goes down.
There’s a small chance you fried the MREQ line of the CPU.
At this stage, it looks like the ROM, the CPU and the ULA are all at least partially working. Most likely suspects remain any of the RAM chips. So far no RAM has been eliminated.
No, you can’t rule out upper RAM completely. Then again, since the screen is part of the lower RAM, and it looks like the screen isn’t corrupted, it might not be lower RAM either. I just suggest a method of eliminating potential causes one by one. Technically (albeit, very unlikely) the problem might be with the ROM itself, or, possibly one of the address or data lines.
Bah. Tell me about it! We need to coordinate better.
ZX 81s yes, 128Ks virtually exclusively, but for 16/48K it was a rare spectacle. Hence, my suspicion. But the board does look like it’s all original parts. On the first pic, the soldering job on the CPU had a suspicious shine to it, though.
Oh, absolutely.