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

After autotune rutine the display always shows "-- --" (Manual function) when you press two digits fromt he presets then the dipslay change. 

The eproms seems to be fine, if one it's not working the autotune routine never start. The "D" Eprom only is available when the OC-8 is installed and the Version is 3.2.

Try to check the DAC if you see the lines comming from the control panel and keyboard. Also check the Kbd Buffer (IC10) Kbd Bus Latch (IC11,12), the I/O Address Decoders (IC1,2,3,4,8) the comparator IC31. Many many things to check

I had a problem like that with a Juno 60 and the problem was the keyboard MPU.

What's the serial numbers of that JP-8 ? is it comes with DCB, 12 or 14 bit's DAC ?



--- In vintagesynthrepair@yahoogroups.com, "souldream70" <paulopalmieri@...> wrote:

>
> 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
>