Re: Trying to fix two broken Poly-800
- Case #1 sounds similar to my recent fix, lights but no button action, key sound.
After verifying the supply voltages, check IC33 and IC34.
In my case, the unit was stored standing upright, and the batteries were left in. The cells leaked, and acid dripped onto the main board and ruined the chips along the edge.
Look for corrosion on the ic legs in and around this area.
These chips buffer and demux the keyboard and button signals.
--- In email@example.com, Michael Hawkins <korgpolyex800@...> wrote:
> First, how do the power supply voltages look?
> From: Malte Rogacki <gacki@...>
> To: firstname.lastname@example.org
> Sent: Thu, December 31, 2009 4:15:52 AM
> Subject: [korgpolyex] Trying to fix two broken Poly-800
> Hello everyone;
> new group member here. I've recently aquired two non-working Poly-800 which
> I'm trying to repair now.
> #1 is an "inverted" model, without a battery on the main board (but with
> the solder pads for it) and without a KLM-601. #2 has both the battery and
> the KLM-601.
> #1 occasionally powers up so that the display lights up; however it doesn't
> react to any button presses and makes no sound. About 50% of the time not
> even the display works.
> I've observed RST 5.5, 6.5 and 7.5 and they look pretty normal so far. What
> somewhat irritates me is that the CPU clock looks more like a sine than
> like a rectangle. Is this normal?
> #2 seems to have a problem in the RESET circuitry; pin 36 of the CPU reads
> only around 1.9 volts which I believe is not sufficient. The CPU clock
> looks more or less "sinusy" here as well.
> I would be most grateful for any ideas how to get them running. Right now
> I'm planning to move IC40 from #1 to #2 to see if that helps things with
> the RESET line.
> The material in the files section of the group has already been of major
> help here.
> Thanks and best regards,
> Malte Rogacki
- More progress (or non-progress):
I got me another Poly-800; this one is actually working (except a display
problem); and so this gave me the chance to swap certain components around.
Ironically, this third Poly is again a different revision compared to the
As I wrote earlier, one of the Polys seems to have problems with the RESET
circuitry. By moving a few key components between the working machine and
the non-working one I was able to find out the following:
1. RESET voltage is around 1.7 volts instead of 5 volts.
2. IC40 is not the culprit.
3. DTC2 is also working (in the sense that the component is not blown).
4. When removing DTC2 from the non-working machine I get a proper RESET
voltage of 5 volts.
So, does that mean anything? Could it be that the 6116 is responsible?