Search found 11 matches

by DistantStar001
Tue Feb 13, 2024 10:08 am
Forum: Hardware
Topic: 250407 Board with an AC power issue
Replies: 2
Views: 73

Re: 250407 Board with an AC power issue

Fixed. The 74LS193 at U30 was defective.
by DistantStar001
Mon Feb 12, 2024 11:58 pm
Forum: Hardware
Topic: 250407 Board with an AC power issue
Replies: 2
Views: 73

250407 Board with an AC power issue

I've been working on this board for some years now. Worked fine for a long time then stopped. However, I think I've narrowed in on the issue, I just don't know what's causing it. Using a Ray Carlson PSU, the 9v line puts out about 9.5 to 9.6v consistently. This is verified when plugged into the boar...
by DistantStar001
Wed May 04, 2022 9:29 am
Forum: Hardware
Topic: 250425 Board repair/One Flash on dead test
Replies: 7
Views: 1565

Re: 250425 Board repair/One Flash on dead test

Success!!! I missed a floating pin (pin13) on U13. Hey, I just realized! Unlucky 13!!! But it's working now! :-D
by DistantStar001
Tue May 03, 2022 8:53 pm
Forum: Hardware
Topic: 250425 Board repair/One Flash on dead test
Replies: 7
Views: 1565

Re: 250425 Board repair/One Flash on dead test

I just moved that exposed wire back in contact with the adjacent pin and am getting the single flash again. I MISSED A TRACE!!! The patch is on the 74LS257 at U13 (a RAM multiplexer I think). I'm going to have to follow all the traces again to figure out where that goes.
by DistantStar001
Tue May 03, 2022 8:40 pm
Forum: Hardware
Topic: 250425 Board repair/One Flash on dead test
Replies: 7
Views: 1565

Re: 250425 Board repair/One Flash on dead test

levoman wrote: Tue May 03, 2022 10:11 am According to this site D1 is U9 not U12??

https://myoldcomputer.nl/technical-info ... 5-01-c64b/
It is. But the dead test can present certain RAM failures as a fault in data bit 7 when the real fault is in either bits 0 or 1.
by DistantStar001
Tue May 03, 2022 8:31 pm
Forum: Hardware
Topic: 250425 Board repair/One Flash on dead test
Replies: 7
Views: 1565

Re: 250425 Board repair/One Flash on dead test

I am assuming that you have swapped the ram chips around to see if the error follows either u12 or u23 and have checked for data bus shorts to ground with a multimeter? The results you are getting would indicate to me either a ground short on D4 ( u23 data ) or more likely a short between D1 and D4...
by DistantStar001
Tue May 03, 2022 12:00 am
Forum: Hardware
Topic: 250425 Board repair/One Flash on dead test
Replies: 7
Views: 1565

250425 Board repair/One Flash on dead test

As the title says, I'm trying to repair a 250425 board that's giving me a single flash on the dead test. I've conducted extensive repairs to the board, removing and eventually socketing almost every single IC on the board (and at this point, all the ICs that went in them). The only exceptions are th...
by DistantStar001
Wed Apr 20, 2022 7:35 am
Forum: Hardware
Topic: Need a clean image of a C64 250425 PCB
Replies: 3
Views: 976

Re: Need a clean image of a C64 250425 PCB

I've actually made some progress today! Going over the board, I've managed to locate and patch 8 broken traces on the board, and have begun repopulating it with machine sockets. In hindsight, maybe I should have slipped in a few zifs for future testing, but I wasn't sure that the board would be salv...
by DistantStar001
Thu Apr 14, 2022 10:24 pm
Forum: Hardware
Topic: Need a clean image of a C64 250425 PCB
Replies: 3
Views: 976

Need a clean image of a C64 250425 PCB

So getting down to it. I've been trying to repair a 250425 C64 board for a few years now. It worked when I first got it, then stopped. And over the years, tracing various faults, and replacing literally every single IC, all I get is a black screen (even on dead test). Suffice it to say, the thing ha...
by DistantStar001
Thu Dec 03, 2020 7:57 am
Forum: Help!
Topic: C64 3rd party mouse issue
Replies: 4
Views: 4097

Re: C64 3rd party mouse issue

OK! So progress... First: It's a Contriver Technology inc. mouse, model M1, not "Computer Technology". God, that text was small! Second, after another round of Googleing, I was able to learn that the odd angles of the LEDs and sensors were not normal, so I bent them back. Sadly. this has n...