Vintage Synth Repair

I would certainly not rub IC legs with any abrasive let alone something like
wet and dry emery cloth.  The legs are probably plated could be gold flash
or one of the other precious metals so any abrasive will remove it and make
the contact worse.  Use Deoxit on a cotton bud.

 

Regards

Brian G3OYU

 

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Scott
Sent: 11 May 2011 4:37
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re: Sequential Circuits Pro One schematic help

 

  


--- In vintagesynthrepair@yahoogroups.com
<mailto:vintagesynthrepair%40yahoogroups.com> , Tom Russell <russelltc@...>
wrote:
>
> The fact that you get intermittent signal when you press on pins sounds
like a bad mechanical connection somewhere, either in socketed chips, bad
wire connector(s), broken PCB trace(s), bad solder joint(s), things like
that. 
> 
> Get a good lighted magnifier and check the board. I'm not intimately
familiar with he construction of that particular synth but if there are
soketed chips with the "spring leaf" type sockets replace them with
collet-pin types which are much more reliable. You can also try removing
chips from sockets and see if there is oxidation on the legs and or the
socket pins. Clean them with some Deoxit or similar, Unplug multipin
connectors and see if the pins are oxidized.
> 
> Remember these things weren't designed and built to still be working 30
years later- only until the "next" model was available!
> 
> --- On Tue, 5/10/11, Mark Milanovich <casiotone1331@...> wrote:
> 
> From: Mark Milanovich <casiotone1331@...>
> Subject: Re: [vintagesynthrepair] Sequential Circuits Pro One schematic
help
> To: russelltc@...
> Date: Tuesday, May 10, 2011, 8:48 AM
> 
> Tom,
> 
> Thanks for the insight on the problem.
> 
> I did what you suggested. No signal at all on pin 10. So I started poking
around to see if there was a cold joint or something. I ended up finally
getting signal on 10, without doing anything! Signal also popped up on pin 7
of the tl082.
> 
> In the meantime, I found out why I wasn't getting any output. The 5532 was
bad, after I changed it with a socketed chip I immediately got output. The
bad news is the oscillators sound pretty messy. The waves look fine on the
oscilloscope, but I noticed the amplitude is very low. Master volume now
works but for some reason I feel like the waves should be higher in
amplitude. Osc A is extremely quiet. Osc B works ok with squarewave but is
quiet on the triangle and sawtooth. Not only that, but when I start detuning
the oscillators, I get an audible clicking or thumping that goes away when
tuning back to zero beat. What could cause this?
> 
> Back to the filter, though... still not working. I seem to get output on
pin 10 at very spotty intervals, and the signal passes through the other
pins most of the time. I can't say how often, sometimes when I touch pins 4
or 5 on the 3320 I get a wave and sometimes I don't. Its weird. When it is
working the changes in cutoff and resonance do not affect the signal. When I
get nothing but a straight line on pin 10, it bounces up and down when a key
is pressed.
> 
> I'm starting to get a headache! This synth is a mess!
>
On socketed ICs it's good to CAREFULLY pull them and buff the pins with a
autobody type sandpaper ( like 600 grit or finer)
Lay the sandpaper flat on a table and rest one side of the IC on it and buff
gently....I've just recently did this to one unit
The other thing to check is power supply ripple on the pwr pins of the ICs.
A DC meter will only show the DC component of the supply volts.