Roland HP2900G has no sound at the keys

I have a Roland HP 2900G, no sound from the keys, no sound from headphone jacks. I have power to the circuit board that has 4 fuses, all are good.
I cleaned the volume slider with contact spray.
If I take the fuse out next to where the power comes in , and use my tester it has power, it seems the other 3 fuses arent getting power at all.
Also the circuit board that has the vol and brilliance knobs also has some issues. some of the buttons are broken, however the little switches underneath appear to light up.
Im wondering if just changing that board that houses those switches might help?
Also I plugged an electric guitar into the back of the unit, and it works properly, altho the volume on the keyboard did not change the vol on the guitat, only the vol on the guitar did.
Any help would be much appreciated.

THanks in advance

Fuses are fine - 1 fuse before the transformer 3 fuses after the transformer for +12VDC, -12VDC and +5VDC. We can assume that the +12VDC and -12VDC must be OK else the line-in signal would not amplify through the main out as the buffer IC’s do use those voltages
Line-in signal is mixed with the internal signal AFTER the volume pot - so volume pot has no impact hence that is fine also.

I have to dig more for the next part … a bit later …

Thanks for that response, just curious if you have had a chance to look further?

Thanks again