Can you post a picture of the whole MPU board with the wiring connected at the bottom of the board?

Just partially worried about battery leakage/corrosion.

It's a WPC-95 CPU and the batteries are at the top/left of the board. The switch matrix is at the bottom. I'm not saying that any alkaline damage cannot reach there but it's less likely on WPC-95 than on WPC-89. WPC-95 alkaline damage usually takes out U5 and U27 before it gets near the switch matrix. I have one where I repaired damage to those as well as U4, U9 and G10 all on a single board.

Can you check the ground braid behind the CPU-board. (red circle) Is it touching the backside of the board at J205 ?

If not, start with the outputs of U16 (pin 1,2,13,14). (red square)
They should all be High (5 volt) when buttons are not activated or J205 is disconnected.
'volume up' is pin 1 of U16

Naamloos-1.jpg

That test is useful, it shows that the inputs of the LM339 are not being pulled 'LOW' by a switch or any other cause.
Now the outputs of U16 are next to measure (see post #9)

That is all what it is supposed to be.

This could mean that U15 is corrupted or even problems with data around processor/ram/asic

Does pressing on the ASIC chip U9 help?

And yes, a single picture is worth a 1000 words. I just find asking for pictures right away does help rule out some possibilities. This one did have switch errors and you can see anything is possible. In the case, most of the corrosion is on the back of the board. This seems quite impossible, but there it is.

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The front of your board looks good, so I'm not expecting damage on the back. Just wanted to show why I was asking for a picture.

As I mentioned on post #14, try pressing on the U9 ASIC chip to see if it fixes the max sound issue.

zaza always on point. Thank you for posting here.

This was an interesting one.
First it was pointing to the switch inputs at J205 because of non responding buttons. But after having a correct signal at the outputs on the LM339 but still a "volume up" on screen, it was clearly something deeper in the CPU.

Glad that pressing ASIC as you suggested solved the problem and saved the ears of cami2305

MPU = Multiple Problem Unit
Play ball !!!

cami2305 I hope you get NVRAM installed in the near future to protect this perfect board. I hate batteries.

I once had a lamps issue on my AFM that I could not figure out for a long time. I tried everything I could think of with no success. Someone told me to push on the Asic chip and VOILA! Fixed it.

can you explain what we should be seeing in these images? It looks like the back of the board around U23 is pretty gamey. That can’t be battery corrosion, can it?, it’s so far away from the battery holders.