Yes, the cpu tester was once again very useful. I had to make up another heap of cables to connect it, but I should be right now for any future boards from WMS sys 3 - 11.
Following clays guide, I set about replacing the rom chip sockets on this board.
I was able to easily remove the plastic casing on all but the machine pin socket. It is certainly much easier to remove these socket pins one by one, than try to desolder the entire socket at once.
I think the machine pin socket was probably ok, but I didn't really like the look of it so I ended up replacing it as well. I used side cutters to carefully breakup the plastic around the pins before removing them one or two at a time.
After all the old metal legs were removed, I used a cheap soldapult and plenty of flux to clear the holes. After this I cleaned all the flux off the board with isopro before checking all traces around the sockets and installing new machine pin strip sockets.
I wasn't too sure about the piggyback rom setup and to be honest I got quite confused while reading the roms section of Clay's guides and had to re-read this part about ten times!
Eventually I figured that I needed to move the jumper wire from J4 to J3, so that i could use a game rom at IC14 and not have to use the top three sockets. (IC26, IC22, and IC21)
I tried to boot the board using the supplied piggyback rom chips, but the cpu leds still just flash and lock on.
Hmm. Could this also be a problem in the blanking circuit, just like my last repair?
Unfortunately not. After getting all excited and replacing the capacitor and transistor in the blanking circuit, everything was still the same.
I did notice at some stage that if I pressed down on IC15 while powering on the cpu, that one of the leds would go out, which was at least some progress. Cut off the old chip with a dremel and socketed and replaced a new chip but this still didn't seem to make any difference.
Time to concentrate on the roms as i really didn't know what was on the piggy back chips, so I pinched the roms from my Stellar Wars and tried them.
CPU booted straight away, leds flashed and then went out as they are supposed to.
Took the opportunity to print and apply some fresh stickers to my Stellar Wars chips as well.
More to come.
