Vintage Synth Repair

hi list,

i just got an MS20 (i think its mk2 version with the screw on the vca section.).

it has some problems in its patchbay:

the S/H does not work (the output does not output any stepped voltages, so i cannot know if its the sampling or the clocking section that does not work), 
the linear VCA also does not work, 
the White and Pink noise output does not work (and the noise waveform in vco1 does not work either) 
and the pitchbend output does not work.

any suggestion on what to look for?

are these repairable? 
or do these sections contain any custom unobtainable korg chip?

of course, i will give it to my tech to repair it, but any general help and guidelines are very helpful.

all other patchpoints and functions work fine.

any help?

many thanks in advance,
best regards,   :-)
Bakis.


Bakis Sirros - Parallel Worlds / Interconnected / Memory Geist
[Doepfer_a100] group owner
www. parallel - worlds - music. com
www. myspace. com/ parallelworldsmusic
www. myspace. com/ interconnectedmusic
www. myspace. com/ memorygeist
www. DiN. org. uk
www. musicamaximamagnetica. com
www. shimarecords. co. uk
www. rubberrecords. gr
Athens - Greece

The good news is: Everything can be repaired. It's just the question of
identifying the actual problem.

Let's start from the bottom:

> and the pitchbend output does not work.

That's a broken connection or the pot is broken. No active components in
sight here.

> the White and Pink noise output does not work (and the noise waveform in vco1
> does not work either)

This probably means the noise generator itself is dead (the noise waveform
in vco1 comes from it as well).

> the linear VCA also does not work,

Hmmmmm....

> the S/H does not work (the output does not output any stepped voltages, so i
> cannot know if its the sampling or the clocking section that does not work),

You know, this is getting interesting.

Does the headphone amp work? If it doesn't the problem is very easy to fix.

-- 
Malte Rogacki gacki@...
----------------------------------------------------------------------------
"Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason why you
 get no sound out of it." (ARP 2600 Owner's Manual)
----------------------------------------------------------------------------

> also the headphone output is very low.
>
> any ideas?

Since all the affected functions/modules reside directly on the KLM-128
board (the patchbay board) I believe that at least one of the supply
voltages is missing (or misbehaving) directly on this board. So my first
attempt would be measuring the supply voltages at various points. I'm not
completely sure but I think the supply enters KLM-128 on connector H4.

-- 
Malte Rogacki gacki@...
----------------------------------------------------------------------------
"Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason why you
 get no sound out of it." (ARP 2600 Owner's Manual)
----------------------------------------------------------------------------