Woo hoo - Collection Completed!! TRS-80 inbound

[Tomswork]

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

Tom

[stephen_usher]

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

[rubber_jonnie]

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

Looks like it, yeah...

[rubber_jonnie]

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

[rubber_jonnie]

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.

[stephen_usher]

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.

[rubber_jonnie]

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.

[rubber_jonnie]

Well, that's the new sockets installed:

PXL_20220929_172653203.jpg

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.

[stephen_usher]

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

[rubber_jonnie]

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

No, but it's certainly tempting...