JX-8P Repair.

This time, I got a JX-8P in a mint condition apart from two voices that posed a problem with the VCF.

Pretty vintage machine!

After passing the test procedure, it was obvious that voices A and E posed a real VCF worry. In a first time, as I had the same kind of problem with a JX10, I thought I was in the same situation so I ordered two IR3R05 :

And placed them on two IC sockets :

Ok! And does it work better now? NO. Too simple!

No choice, I have to test the control voltage coming from the two ICs, CD4051 (IC44)  and the TL064 (IC51) :

I noticed that effectively, the voltage comming from the par C and D of the IC51 (TL064) didn't match the requierd values. So I replaced this two ICs, the TL064 (TL084 works fine in place of the original TL064) and the CD4051 (IC44). As I was there I also replaced the IC43 (CD4051) circuit which supplies the voltages control for the VCA part of the IR3R05 :

The three ICs on socket.

After this modifications, the voice E working good but, the voice A did not provide any sound. I had to go to the next step and use the oscilloscope to determine that the capacitor C88, whose role is to provide the sample and hold function, was in fact in short circuit with the ground. I nerver had this problem before with this kind of interface in a Roland hold synth! I replaced this capacitor with a new one in smt version. I soldered this 805 type capacitor on the other side of the board. After this last modification, all the voices were working very good : Yes!

Finally, troubleshoot this JX-8P was not very difficult, even though I have now two IR3R05 fully functionnal in stock. I will keep them preciously, just in case...

Inside this JX-8P (before my repairs) :

No dust, no mold, no rust and no... beast : absolutely perfect!

Not even blackish traces of heat on the power supply!

Good, but before reassembling the machine, there is again to take care of the backup of the static ram :

 
I decided to have no more problem with the backup battery. So I made a copy of my auto-saved SRAM :

It's a solution that works perfectly for a stand alone auto-saved replacement for the 6116 SRAM. I also have a version to replace the 62256 type SRAM. Before it's installed in the JX, I tested it with my EPROM programmer :

OK, it's time to put it in place :

Of course, no more battery is needed :-).

The internal patchs are reset at startup :

But, after copying the preset number one into the internal number one memory, and after restarting the JX, the patch number one is still present :

Voilà, a superb vintage synthesizer ready to play again for many years!