Interesting C64 fault

[Mike Brixius]

While I'm waiting for the parts to come in for the pet i decided to get a ZIF-64 put together out of some old parts for my plan to fix 64 64s in 23 -- which, if you reverse the digits then double it is 64 --

Anyways i took a 250407 rev c that the original owner was using for parts. A lot of ics had already been desoldered very neatly so it seemed like a good candidate. After installing ZIF sockets and populating the board with everything but a SID i was pleased to find only 1 74ls257 needed replacing.

Then i installed the sid and on power up i get a crackle in the speaker and a black screen. Now i know that a bad sid can cause this so i installed a swin-sid i keep for testing and got the same result.

Interesting. I'll put the scope to work on the morning but i thought it was unusual.

 

[NoPizzaTonite]

If you're sure your SIDs are not damaged, I would start by checking the socket/traces since a shorted SID can cause that black screen and you state you have a working system without it.
Did you use a diag cartridge without the SID in place to check for errors?

Even though I have a bunch of test equipment, I built a zif-64 as well to keep my backbit pro tester in check

Good luck with the troubleshooting!

 

[Mike Brixius]

Yeah it passes fine without the sid... except the expected port and sid error. I'll triple check everything this morning. I checked for adjacent shorted pins and everything toned out fine. With power on it has 5 and 12 volts. I'd say i visually inspected it very carefully but the last thing i had to do to get it running was replace the missing 7805 i had not noticed was gone. This was someone's parts board back in the 90s.

 

[Mike Brixius]

Ah, the power of fresh eyes in the morning. The SID is indeed shorted. The BackSID (Not Swin-sid as I said earlier) was not fully seating in the ZIF so it black screened because it was only partly connected. Putting it into a socket then into the ZIF and it works fine. Both still have a short burst of static on power up, which is not present with no SID installed, but the board is working fine otherwise and passes all Diag tests. That static led me down the trail of thinking it was the board.

Now I can get to testing a couple tubes of old (old old stock?) CIAs, CPUs, a couple SIDs and many ROMs that are labeled as "May be good". Karl seemed to REALLY love Jiffy Dos so he had a TON of original ROMS laying about. I even found a NoS R4 SID rattling about in the bottom of a file drawer full of junk.

Mike

 

[NoPizzaTonite]

Happy for ya narrowing down the issue. Nice job!