Back to the drawing board.
Looking at diagnostic pictures and my remaining socketed chips I was getting down to a last man standing situation.
I only had 5 chips left, CPU, CIA2, PLA, Color Ram and two identical logic chips.
PLA - ease don't
I guessed the PLA ( I had two spare ) and got to work de-soldering it very, very carefully
WARNING : apparently it is very easy to kill it by removing it.
I eventually got it out very cleanly. I put in a socket and then inserted a new PLA and got this.
Ugh Oh, that's not right. I put the original PLA back in the socked and got the same picture. I pulled out the multi-meter and began checking all of the connections, nope everything was fine. I then checked for shorts. I already knew that two of the pins short when a cart is attached so I removed it. I quickly found the short between two pins connected to the Colour RAM. The solder had joined under the socket. With a piece of copper solder wick I jammed it against the side of the socket and it cleared the short and I went back to the black screen.
The Final Culprit - CIA2
Time to pull CIA2. So I got to work and removed it and powered it up without CIA2.
Now we are getting somewhere. I quickly socketed it and jammed in my two spare good CIA's.
I replaced 3 x logic chips ( status unknown, one was probably dead ).
1 x ram chip ( dead ), 2 x CIA chips ( dead ), 1 x SID ( dead ), 1 x 8701 ( dead )
Was it worth the repair. Cost wise I'd have to say no. If you wanted to have C64 that works just buy a working one.
Education wise, yes it was a great exercise. On the plus side I now have a test board with almost all of the IC's socketed. I buy this dead stuff to learn skills and my through hole soldering is so much better now.
I'm also pretty pleased I got the PLA out in one piece. I've read it's quiet hard to do without killing it.
No comments:
Post a Comment