exxos's Atari, Amiga & retro forum

Over the years I've had a lot of ttl oxide just inside the package the Fujitsu being the worst

Tom

It seems like you're having similar failures to Adrian Black and his Model II and Model III combined! :-)

stephen_usher wrote: 28 Sep 2022 20:00 It seems like you're having similar failures to Adrian Black and his Model II and Model III combined! :-)

Looks like it, yeah...

Tomswork wrote: 28 Sep 2022 19:59 Over the years iv had alot off ttl oxide just inside the package the Fujitsu being the worst

Tom

This is definitely the worst one so far

So in preparation for the new ICs arriving (74LS05s and 74LS368s) I started by removing the D1 column IC, Z3, at lunchtime. I tested it and guess what, that's dead too.

So I will likely just remove and test them all so I can fit sockets. I also suspect the A5 row IC to have a bad gate, which is Z1, so it makes sense to replace all 4 ICs if I have to remove at least 2 of them.

Sounds like a good plan. I wouldn't be surprised if slowly most of the 74LS logic chips go bad. It does feel like it's had power issues which have damaged chips.

stephen_usher wrote: 29 Sep 2022 14:39 Sounds like a good plan. I wouldn't be surprised if slowly most of the 74LS logic chips go bad. It does feel like it's had power issues which have damaged chips.

Yeah, I agree, the more i've used it, the more it's slowly failed, so I wouldn't be surprised if a bunch more go, especially since the zener that failed was part of the 5v regulation, so the fact it failed shorted suggests an over-voltage on the 5v rail. I am prepared for more failures, but hoping that after this latest round for a bit of a break!!

It might also explain why some of the original RAM ICs were bad too if they had an over-voltage.

Well, that's the new sockets installed:


Just got to wait for the parts now.

All bar one, a 74LS05 tested bad, though I think some have spare gates which is why I only had one bad column and one bad row, as they were partially working and not totally dead.

So, have you ordered a complete BOM for the machine yet? ;-)

stephen_usher wrote: 29 Sep 2022 21:33 So, have you ordered a complete BOM for the machine yet? ;-)

No, but it's certainly tempting...