Vintage Synth Repair

Hello everybody,

I´m blowing my brains to repair a Jp8 and I decided to claim for help...

When I power on the synth, it runs the autotune normally but after autotune is completed, no keys in the front panel operate, no functions and the display only shows -- --.

The most important issue is that the "D" eprom (IC33)was replaced and it´s not original.
I have tested this IC in my Eprom Burner. an Elnec Memprog model, and it was ok.

Also, I checked the data bus and address bus with an scope and found unstable signals in the lines. The waveforms are present but they varies the amplitude fastly, I don´t know if I´m being clear.

The power supply is ok. All the voltages are present appearing in the correct values as I have checked with the DVM.

I checked all the RAM banks, replaced the UPD444c ICs with no success.

I have tested the Eproms A,B and C in the Eprom Burner and they are ok.

Is there anyone who can help me or have the Eprom data files to send me? or a link?

Thanks in advance!

Paulo Palmieri
www.vintagesynth.com.br