Playchoice-10 repair #2

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Jun 172020
 

Another challenging PlayChoice-10 PCB repair!

The symptoms were that I could see the menu but there was no game – just a black screen. Triggering the game to start allowed the game to play blind, so pretty much the opposite of the board I had just fixed. Initially I thought it might be a sync issue.

I could see issues on the 4066 @3C and LM324 @3E but couldn’t pinpoint anything exactly.

I looked through all the logic from the CPU/PPU up to the game card, and I couldn’t see any issues.

What’s odd is that the menu system goes through the same sync chips, so you would expect both screens to be not showing, so that was a bit of a mystery to me unless I got it wrong?

I got the scope out and sync looked ok, but the colours were not. The failure seemed to be occuring just after 2E in the colour section. At this stage I took a guess and replaced the LM324 @ 3E as that tied colours together.

This did not fix the issue, but it helped me determine that there was no 12 volts coming into the colour circuit. What was baffling was that this board does not use 12 volts, but instead it uses a DC-DC converter to convert 5 volts into 12 volts and this was missing as I had a reading of 0.8v! What also made it hard was that the schematics do not cover this version of board (PCH1-04-CPU) and this specific area, so I spent quite a while working out what was connected to what.

The RK13 diode @ D5 was ok, which I also suspected as being faulty.

I replaced the IR3M03A DC-DC converter with an MC34063AP1 and still no 12 volts!

I then noticed that R32 was burning up so wasn’t sure if there was a short somewhere, but as soon as I removed this resistor and reflowed some components then the 12 volts was backā€¦so having looked at the schematic, something along it’s path was causing it to overheat. If I again replaced the resistor it would melt.

Then I noticed that the PCB had quite a bit of corrosion on it in the colour section. I thought this was likely causing the issues so I ended up replacing:

Variable resistors VR1-3

Transistors Q12,Q13, Q15,Q16, Q18,Q19

Capacitor @ C20

These were A933, C1740 transistors, and some 500ohm pots, and a 470uf axial capacitor.

I powered up the board and was glad to now see that the resistor R32 was no longer burning hot and melting.

However the game still did not play! It just froze on the menu.

I spent an hour or so looking at issues, and in the end I tried the same game cartridge on another PCB, and found that the game cartridge had now failed! When I put a known working cartridge on the corroded PCB it confirmed that the game was working, everything was fixed and the replacement parts did he job!

The issue with my failed game cartridge (Golf) turned out to be a failed Eprom @ U3. I replaced this and the game no longer froze.

Playchoice-10 repair #1

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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!