Korg M500 Micro-Preset -1977     Weight = 10.5 Lbs. Number mfg.= ? MRP=$?

User Manual: fdiskc archive
Reset Proceedures: N/A
Operating System code: N/A
MIDI or other control protocol:
Software related Links: N/A
Patches or knob settings:
Circuit Overview: below
Scematics/Service Manual: fdiskc archive or HIGHER RES SCHEMO (1 page) Tony Algood
Common Service Issues/Tips: below
Parts Sources: Keys knobs semiconductors misc
Uncommon chips/modules used: 2- Korg 35 VCF
General Info Links: VSE or Synthmania for sound samples etc.

Circuit Overview:
     A 6 preset voice machine with the traveller filter with similar sounds to MS-10. There are actually two Korg 35 filters in these. One for the traveller lpf slider and one for preset arrangements. The first button accesses synth footages witha preset sharp attack. Second one gives you the variable attack and decay knobs. And two of the footage selects (every other one) are noise sources (white and pink). Third button gives you the traveller still but preset envelopes and the last three are preset filter settings with only modulations and portamento adjustments. Love that Tuba, bassoon and Oboe!

Service Tips:
      NOTE: REPLACE THE 220UF 16V Capacitors! They WILL leak and destroy your traces that are unprotected. If they are damaged it's best to just wire the connections to the integrable points that you will find on each end of the traces area of damage. ALSO the 33UF caps may cause damage so replace those as well minimally.

Here's an excerpt of one horrifically bizarre repair. All I can say is, if the attack knob acts like a cutoff, you might try replacing TR29. :

It was late but I got it done.  I don't understand it.  I shouldn't have tried to use the scientific method.  lol. 

So basically I monitored and compared the trigger signal and it was all the same to the attack pot.  But then clearly after that some leak was dragging the voltage that should have gradually got to 5.8V...... down to 2.6V or so with the pot halfway up.  And then it would just move up and down as you move the attack pot so the pot became effectively another cutoff freq. control!  We already have one so..not so useful :-)

I measured leakage with the diode checker and it was same on the other side of the attack pot as it is in the working unit but on the other side of TR29 it showed a leak where there was NO leak in the working unit there.    So I first pulled up the 10K resistor going to the vcf but that made no difference at all as expected.  I measured across the 820K in case it was mismarked but I got nothing across it as expected.  I'd already done flux cleaner so I'm puzzled because the only remaining ROUTE for the current .... is through TR29...but it got to 12 volts!!!!!!!!!!!!!!!!!!!!!!!!!!

Well... I pulled it anyway since I was measuring what looked to be a possible reverse leak and indeed..the damned thing leaked!   I replaced it and all is well!

But..how?  what?  How did 12V pull 5.6V DOWN to 2 V etc.??!!!!  (serial number 770788 on that one.)

I can't recall what all I had to do besides filters on mine... serial 771129 I think it is. Ineresting, one on ebay is 791359 so maybe the 79 is the year of production in those days. I have 770098 in the PE-1000 and so that blows my thought that Korg was putting model codes in the first digits :-). Sooo... Anyway the manuals are online. Japanese capacitors seledom seem to go bad in these things. However the 10uf 16V units used for coupling ARE always suspect. If a particular section drops out try that first. Usually connection or potentiometer issues probably otherwise.

I probably have some parts for these. I do not have Korg 35 vcf's but they rarely fail. Delta slider caps work nice which I have.
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