MS8-26a troubleshooting

[gigasturtz]

Have a few ideas. First, I inspected the board some more, removing the solder from potential shorts, and found this:

Looks like the pads were a little torn up on the bottom two, the lead from the one was initially bent over towards the other. I also think the top right point may have been shorted to the blob of solder that was connecting the two with the messed up trace. I sorted that all out and will try again when I get a replacement fuse (and a few spares…).

Going to test this and will follow up with my second theory if it doesn’t work.

 

[gigasturtz]

Getting a voltage reading of 165v at the fuse now. Any suggestions for where to look?

 

[gigasturtz]

Found this manual, which included some troubleshooting information.

https://wiki.arcadeotaku.com/images/e/e5/Nanao_MS8-26SU_manual.pdf

This part in particular was relevant to my situation:

My voltage is still reading 165v at that spot so I inspected the Q901-903 area. I found the fusible resistor next to Q901 wasn’t reading the appropriate value, pulled it out and it had indeed blown.

I’ve ordered a replacement as well as replacements for Q902 and Q903 in case they are also blown.

Additionally the manual suggested testing the resistance from the other side of the fuse to ground, stating that values between 2-4K means the circuit on that side is fine. Mine reads around 3.3K now, so I’m hopeful that this fusible resistor is the answer.

 

[gigasturtz]

Replaced the fusible resistor next to the C3306 and no luck. Going to replace the transistors next to it as well.

 

[gigasturtz]

Swapped the 2SC2610 and 2SA91091 near the C3306 and still getting the 160V reading at the fuse. Will pull the resistors and diodes in that area to test them next.

 

[gigasturtz]

Frustrated with myself again, realized I put one of those transistors in backwards. Pulled it out and it’s still working, put it back the right direction and everything is still the same. Hoping I didn’t blow something else up with that component the wrong way.

Back to testing the other components in that area one by one I guess!