Vintage Synth Repair

Dear Randy [and list ]
the Oberheim OB-8 uses the cem 3340 oscilator ic.
its possible that that might be the fault , but it could be something
else .
if the ic's are in sockets you could try carefully swapping the ic with
a known good one [ always turn power off and pull out the mains plug
when you try to swap parts ! ].
it should be possible to work out which voice ic is the one that is
misbehaving from the service info .
data on the cem 3340 and other ic's can be found at 
http://www.synthtech.com
regards Peter

Dear Peter (and list),

thanks a lot for your info about the Oberheim oscillator.

First I would like to tell you, that I will make this entire OB-8 repair 
session available to everyone on a free website (geocities e.g.) like Jetboy 
Junction
http://www.egad.net/too1.html did for a Oberheim OB-Xa., with repair 
description + photos, wav files and even short videos (mpeg or similar).

Would you like to help me a bit now and then when specific problems come up?

The first thing which I will do is to record the strange noise made from the 
broken oscillator(s), when those get tuned by the autotune mechanism before 
they get turned off. I will then make this recording available on this 
upcoming OB-8 repair site, so others can check out, if this might be the 
problem which they are looking for.

Next I will swap ICs a bit around as you suggest.

But in order to be able to do this I have to solve another (probably trivial 
for you experienced technicians ...) problem first:

I must remove the upper 4 voices board on the OB-8 to be able to get to the 
four lower voices. But one of the screws on the upper board is worn out.
Clint Swartzlander says in http://www.egad.net/too1.html

"Also, be careful when you remove the screws not to strip them out. 20 year 
old lock-tight can present problems. I'll typically put some isopropyl 
alcohol on the screws to dissolve the glue."

I read this only afterwards the damage was done  :-(((   . Now I have this 
bad screw on the upper board and it is impossible to remove it with an 
ordinary screwdriver. I friend of mine told me, that the only possibility to 
remove the bad screw is to drill it out with a drill machine.

But I don't want to drill it out, there is the possibility to damage the 
circuitry on the board with such stark methods.
I would prefer another method. Do you know of any method/means to remove 
this bad screw?

O.k. that's all for now.

I really thank you for any help or advice.

Have a great day,

Randy.


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Hi Randy,

I had a similar issue with a screw.

I solved it by using a tiny saw to make a groove in the screw head.
I could then use a flat end screwdriver ease the screw out.

Regards,
Fin

----- Original Message ----- 

From: Randy Lobber <loandreas@...>
To: <vintagesynthrepair@yahoogroups.com>
Sent: Tuesday, December 11, 2001 8:43 PM
Subject: [vintagesynthrepair] Re:To repair an Oberheim OB-8 oscillator.
> 
> I read this only afterwards the damage was done  :-(((   . Now I have this 
> bad screw on the upper board and it is impossible to remove it with an 
> ordinary screwdriver. I friend of mine told me, that the only possibility to 
> remove the bad screw is to drill it out with a drill machine.
> 
> But I don't want to drill it out, there is the possibility to damage the 
> circuitry on the board with such stark methods.
> I would prefer another method. Do you know of any method/means to remove 
> this bad screw?
> 
> O.k. that's all for now.
> 
> I really thank you for any help or advice.
> 
> Have a great day,
> 
> Randy.