Vintage Synth Repair

I have recently purchased a defective Siel DK-600, hoping that it
might be an easy fixer-upper. Now.. what it does when I turn it on
is.. almost all leds are on, the number display in the "program
select" area is stuck at 00 no matter what you press and none of the
other selector buttons seem to work either. Also the led by the
"enter" button keeps blinking. So.. from what I told you what do you
think might be wrong? The battery? It doesn't seem to be just a loose
cable since all areas of the synth seem to be affected. Any hints and
suggestions are highly welcome!

>I have recently purchased a defective Siel DK-600, hoping that it
>might be an easy fixer-upper. Now.. what it does when I turn it on
>is.. almost all leds are on, the number display in the "program
>select" area is stuck at 00 no matter what you press and none of the
>other selector buttons seem to work either. Also the led by the
>"enter" button keeps blinking. So.. from what I told you what do you
>think might be wrong? The battery? It doesn't seem to be just a loose
>cable since all areas of the synth seem to be affected. Any hints and
>suggestions are highly welcome!

Ah, I've got one of these.  Broken of course, I think most of them are at 
this point.  Take the screws out of the bottom, open it up, and lift up the 
keyboard (it's hinged).  You will most likely find that the NiCd battery has 
leaked electrolyte and corroded some stuff on the CPU board.  You'll want to 
remove the battery and clean it up before it gets worse.  On mine the 
battery leaked and disabled the button scanning circuits.. so it turns on 
and makes sound but none of the buttons work.  Until I fix it, I'm stuck 
with a bad-sounding single oscillator saw wave patch.

Another thing that can go wrong (also happened to mine) is that the pitch 
bend potentiometer can short out and blow a fuse.  It's connected to the 
power supply rails, but it's some kind of funky center-tapped 4 terminal 
pot.  I don't remember the exact configuration, but basically when it wears 
out it will short to ground and blow a fuse.

I recently bought a Prophet VS. The transformer buzzes
loudly so I'm planning on replacing it. I bought a
replacement from WineCountry but it appears to be the
same make and vintage as the original so I'm hoping it
won't exhibit the same defects...

The other problem with the unit is a ground hum [~60hz
harmonic] in the audio that follows the envelopes.
It's quite apparent when I turn all the oscillators to
null waveform and close the filter. And it is there
when triggered through midi as well so it is not
keyboard-related. As I'm not experienced enough to
trace and find the problem can anyone recomend a tech
in the Toronto area for this repair?  

thanks!
steve

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what is "winecountry"?
 
Sandra Garcia

----- Original Message ----
From: steve sloan <drbeezar@...>
To: vintagesynthrepair@yahoogroups.com
Sent: Wednesday, May 3, 2006 6:35:08 AM
Subject: [vintagesynthrepair] Prophet VS

I recently bought a Prophet VS. The transformer buzzes
loudly so I'm planning on replacing it. I bought a
replacement from WineCountry but it appears to be the
same make and vintage as the original so I'm hoping it
won't exhibit the same defects...

The other problem with the unit is a ground hum [~60hz
harmonic] in the audio that follows the envelopes.
It's quite apparent when I turn all the oscillators to
null waveform and close the filter. And it is there
when triggered through midi as well so it is not
keyboard-related. As I'm not experienced enough to
trace and find the problem can anyone recomend a tech
in the Toronto area for this repair?  

thanks!
steve

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what is "winecountry"?

Sandra Garcia

----- Original Message ----

--- In vintagesynthrepair@yahoogroups.com, "Scott Nordlund"
<gsn10@...> wrote:
>
> >I have recently purchased a defective Siel DK-600, hoping that it
> >might be an easy fixer-upper. Now.. what it does when I turn it on
> >is.. almost all leds are on, the number display in the "program
> >select" area is stuck at 00 no matter what you press and none of the
> >other selector buttons seem to work either. Also the led by the
> >"enter" button keeps blinking. So.. from what I told you what do you
> >think might be wrong? The battery? It doesn't seem to be just a loose
> >cable since all areas of the synth seem to be affected. Any hints and
> >suggestions are highly welcome!
> 
> Ah, I've got one of these.  Broken of course, I think most of them
are at 
> this point.  Take the screws out of the bottom, open it up, and lift
up the 
> keyboard (it's hinged).  You will most likely find that the NiCd
battery has 
> leaked electrolyte and corroded some stuff on the CPU board.  You'll
want to 
> remove the battery and clean it up before it gets worse.  On mine the 
> battery leaked and disabled the button scanning circuits.. so it
turns on 
> and makes sound but none of the buttons work.  Until I fix it, I'm
stuck 
> with a bad-sounding single oscillator saw wave patch.
> 
> Another thing that can go wrong (also happened to mine) is that the
pitch 
> bend potentiometer can short out and blow a fuse.  It's connected to
the 
> power supply rails, but it's some kind of funky center-tapped 4
terminal 
> pot.  I don't remember the exact configuration, but basically when
it wears 
> out it will short to ground and blow a fuse.
>





Ok.. I have just opened it up. I see the battery and it looks like
there's some kind of corrosion or brown stuff around the solder points
 on the board but can't really see much, I'll have to take it
completely out and put some more light in here. How do you clean that?
What kind of solution would I have to use? I am kind of hesistant
because I'm afraid I'm gonna destroy some of the traces on the board.
By the way my synth does not make a sound at all, it just lights up.
About the "exploding" mod poti... how can I work around that? What did
it to your synth when it happened? Is there a way to ground the pot
elsewhwere other than over the power supply?

>Ok.. I have just opened it up. I see the battery and it looks like
>there's some kind of corrosion or brown stuff around the solder points
>  on the board but can't really see much, I'll have to take it
>completely out and put some more light in here. How do you clean that?
>What kind of solution would I have to use? I am kind of hesistant
>because I'm afraid I'm gonna destroy some of the traces on the board.
>By the way my synth does not make a sound at all, it just lights up.
>About the "exploding" mod poti... how can I work around that? What did
>it to your synth when it happened? Is there a way to ground the pot
>elsewhwere other than over the power supply?

The problem with leaky batteries is that the electrolyte solution corrodes 
the board traces and messes everything up- you'll have to replace the 
affected components and somehow rewire the corroded traces.  There's a 
repair guide here for the Polysix, which also uses NiCd batteries.

I'm not sure about the pitch wheel problem- on mine it shorts out when in 
the center position.  I think I stuck a resistor or something in there, it 
messes up the pitch wheel response, but okay for a temporary fix considering 
there are bigger problems right now and I don't really care for pitch bends 
anyway.  If yours is okay now then don't worry about it, but if the fuses 
blow suddenly for no apparent reason, it's worth checking.

Alright. I finally found the time to take a closer look at this thing.
Now what I have found out so far is that one of the solder spots for
the battery seems to be corroded and that seems to be the only thing
there is other than that the connectors of IC16 are more or less
covered in greenish-gray stuff (oxidation?), so are some of the
resistors and diodes on their ends. What does that mean? needs new parts?

>Alright. I finally found the time to take a closer look at this thing.
>Now what I have found out so far is that one of the solder spots for
>the battery seems to be corroded and that seems to be the only thing
>there is other than that the connectors of IC16 are more or less
>covered in greenish-gray stuff (oxidation?), so are some of the
>resistors and diodes on their ends. What does that mean? needs new parts?

You should probably replace any component with corroded leads- shouldn't be 
anything expensive anyway.  The real problem is corroded traces on the 
board- if they're black looking then they'll have to be rewired.