G'day Rob
Ive now resurrected 2 korgs from dead state, with no display on the
LED's
it seems from both of mine that the issue was with the +5/-5V
generation circuit
The second one also had a dead op-amp in the headphone out circuit
which i managed to get sorted again and both are now happy
To check whether this is the problem with yours, take some readings
at the joystick for the +5 -5V where the connector plugs in
if these are not showing the appropriate voltages, its a fairly good
chance that the 3 input transistors have gone bunky, and not
generating the voltages for the LED circuitry etc
check out Q1 Q3 and Q18 to make sure they are functioning correctly
the schematics for the poly are stored in the archive for this newsgroup
good luck!
Marcus Wilson
On 21/04/2006, at 1:03 PM, Rob wrote:
> Well, the Poly-800 I saved from the dumpster is not looking too good
> at the moment! The bad news is that it has no LED read-out of any
> kind, no flashing, nada. The good thing is, is that as I checked the
> V+ at the input I caught it dropping a few volts and suspected some
> kind of life! I proceeded to connect a set of phones to it and lo and
> behold, the unit gave me a real slow, but sweet pitch, amplitude
> and filter sweep, in stereo several seconds after start-up! It all
> swept up to a max and held. The only thing I can do to the sound is
> tune it with the slider and turn it up and down with the volume pot.
> Absolutely nothing else works. (I can affect the res. and cut-off with
> VR's 2 & 3) So obviously the power, amp, filter and oscillator (not
> necessarily in that order!)sections are working fine. Is there a
> secret button combo or power-up trick that would re-initialize this
> thing or is the back-up and sysex "lost"? The lack of display is a
> bother.
> As you may remember from my previous post, I am a fairly effective
> bench tech and a damn good solderer and I read schematics fine, so
> even if there is something wrong at the component level, I shouldn't
> have any problems doing the fix, as long as someone out there has seen
> this problem before and knows the situation here. Aside from some one
> familiar with this glitch, it will be a stretch. Hopefully it won't be
> a big deal, so if you have an idea, I'll try to raise another Korg
> back from the dead! Otherwise, I have a really huge mono-patch, single
> sweep noise machine.
> I am sure that's why I got this for nothing! But in the words of
> Monty Python...
> "IT"S NOT DEAD YET!!"
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