Jun 172020
 

A fellow collector asked me to take a look at a couple of Playchoice-10 game boards that he was having problems with, as it was beyond his capabilities to repair them, and it was his favourite machine that he could no longer play. I’ve not looked at these boards before, so thought it was a chance to get a bit more familiar with them.

On unwrapping and testing the first PCB I could see that the game played ok, but the menu was all scrambled:

I knew the Playchoice-10 BIOS, which was essentially the menu, was the rom located at 8T, so I suspected that the fault would be around this area. Using a logic probe I found a stuck pin on the ram @ 8R pin 21 in literally 5-10 minutes of looking. I traced this fault back to the LS157 @ 7V. The output of this chip is connected to pin 21 of the ram. The inputs to this chip are pins 5 and 6. Pin 5 was pulsing, 6 was high, 7 was stuck high, so pin 7 had a fault. Piggybacking a new LS157 over this chip, sorted the menu problem so it was time to replace the chip.

Pleased with my repair I put this board aside, and tested it again a few days later before sending it back to its owner. I was very disappointed to find that the board had failed again and this time it was more catastrophic! The board was completely dead! No menu and no game on either screen. The LS157 I had just replaced had also failed! Argh!

Replacing the failed LS157 brought back a scrambled menu, but the game was no longer playing at all. I literally spent hours and hours looking over this board and finally found a problem with the LS00 @ 6U that was causing all manner of issues with the read and write pins in/out of the z80 CPU. Swapped this out and the game is alive again! Hopefully a bit longer this time!