Vintage Synth Repair

--- In vintagesynthrepair@yahoogroups.com, Scott Nordlund <gsn10@...>
wrote:
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> You'll have to go at it with a scope or logic tester or something
and see what's working and what isn't.  There are a bunch of latches
on the data bus that route signals from the CPU to various locations,
controlled by IC8 (port decoder).  I had a couple problems in this
region due to broken/corroded traces, so it may be a good place to
start.  Really, these things are so delicate and poorly-made that
there's not really any single point of failure (how many could
possibly still be in operation?), you have to figure it out on your own.
> 
> To: vintagesynthrepair@yahoogroups.com
> From: cockandswan@...
> Date: Tue, 23 Dec 2008 17:58:26 +0000
> Subject: [vintagesynthrepair] Re: Siel DK 600, strange problem
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>             weird problem. i have a DK 600 too and it doesn't really
work at all.
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> i turn it on and can sometimes get the first lfo's led to flash and
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> one of the digits on the display to light up, but that's it. i've been
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> shotgunning ICs on the board underneath the keyboard and somewhere in
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> there i got the other digit on the display working and i even got a
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> couple of the voice chip LEDs to light, but now it's back to normal.
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> any thoughts? (i replaced the battery too, though i don't think it was
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> leaky)
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> thanks,
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> johnny
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> --- In vintagesynthrepair@yahoogroups.com, Scott Nordlund <gsn10@>
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> wrote:
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> > I repaired the NiCd battery corrosion problem in my Siel DK 600 (and
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> also the Expander module), then attempted to address a CV demux/sample
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> and hold problem (envelope release time was too short because a
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> defective component was draining the charge from the capacitor).  I
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> replaced the associated parts (4051 and TL084), and it fixed the
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> problem, but also introduced some new ones.  The CVs associated with
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> these chips (filter cutoff, oscillator detune, etc.) are unstable when
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> the synth is first switched on, and will actually change (in an
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> interesting way) when there's some kind of mechanical vibration.  It
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> mostly resolves after the synth has had a few minutes to warm up.  I
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> do appreciate the added "vintage driftiness" and "innovative
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> performance controls", but I'd really rather have it do what I want it
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> to do.  I've tried reseating the chips.
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> > It won't be a big deal to just rework the whole thing by replacing
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> all the parts (sockets included) and then thoroughly cleaning off the
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> flux, but the crappy DIP connectors seem to have a very limited
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> lifespan and I don't really want to go plugging and unplugging any
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> more than absolutely necessary.  I'd like to fix it and be done with
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> it.  I'll redily admit that using salvaged components (sockets even)
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> probably isn't the best idea, but I'm too cheap and lazy to order
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> parts, and it's probably not any more likely to cause problems than
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> the original flaky construction.
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> > So based on this, is the problem more likely to be a bad solder
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> joint or bad socket, or is the solder flux on the board interfering
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> with the high impedance stuff?  I'd guess the former, but again I
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> don't want to risk breaking a pin on a DIP connector if I have to
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> rework it again.
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> > There's also some sort of interference that seems to affect the
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> pulsewidth and cutoff CVs (?) of voices 5 and 6.  I probably won't be
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> able to address this without an oscilloscope, but it's not extremely
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> intrusive, so it can wait (though I'm also open to suggestions here!).
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> > __________________________________________________________
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I had a customers unit in here at the shop.
Same issues. The battery had leaked on the main board.
I would say that anywhere you see bluish tint on the board , that's
where some of the battery leakage went. This problem will require
running jumper wires anywhere that the leakage showed up.
Check power supply lines coming into the main board too.
and the encoder that was mentioned by someone else.

Leaking batterys are the Horror show of vintage synths with memory
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