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Introduction
This Commodore 64 (250407 Revision A board with 8-pin video din connector) came to me in an eBay lot of six labeled not working. However, it was able to boot and passed all the diagnostic tests except the sound and keyboard were not working. I covered in a previous case study (#4) how to clean a keyboard which also fixed this one. Here, I show how a socket can prevent a chip and perhaps the entire computer from working.
Case Study
With the keyboard cleaned and working I turned my attention to the 6581 SID sound chip (U18). The good news is that it was in a socket. So, the first thing I tried was swapping the SID out for a working one. That did not fix the sound. I noticed the socket was an old one with only a single line of contacts on each side (i.e. single wipe). This meant that it needed to be desoldered. Desoldering sockets can be a little tricky given it is hard to heat the top of the board with a hot air rework station to melt any residual solder because you will melt the black plastic. My approach was to first reflow each of the pins with fresh solder under the board to loosen things up. I then cleaned the solder chamber and the nozzle of my desoldering iron to make sure it had maximum suction. I needed to get all the solder out and free the pins to avoid needing to cut up the plastic of the socket and remove pins individually which is more work. This technique worked well, and I was able to get the socket out on the first try! Shown below is the new dual wipe socket I installed (I buy these 28-pin wide sockets from Amazon that are suitable for SIDs).
I inserted a working SID chip, and it sounded great. With the cleaned keyboard and the new SID with fresh socket this c64 was all fixed up and ready for a new home.
Comments
This repair was a good lesson in never trusting original single wipe sockets. This is not the first I have had to replace to fix a 1980s computer. I additionally clipped the C1 and C2 capacitors in the RF module for a sharper picture. I also removed the RF shield from the VIC-II video circuitry to make the VIC more accessible and added heatsinks to the Revision 56A VIC-II.