Just bought a poly 800 of the 1st revision. This model does NOT have an internal backup battery inside.

It was working fine for a couple of days (love it !!!), used it with batteries first, then started to use a power supply (not the original one but it worked fine for 2 days).

Then, as I turned it on again, the display showed weird signs for a couple of seconds and jumped back to "P11". No sound. Frozen. From then on, no single button/knob would work anymore - the display either shows some weird signs or "P11" but doesn't change from there, no matter what I push. The synth basically doesn't react to anything at all. If I turn the volume up it just makes click click click.....
I opened the synth, it was a little dirty but I cleaned it and I cannot see anything missing or broken (I am not an electrician though

Anybody can tell me what might be wrong ? Could my power supply have damaged something, and why ? What can I do ?

I'd appreciate any help, thanks a lot !
Bernard