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 a 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.