Vintage Synth Repair

I'm trying to restore an Arp 3604 keyboard.  Several questions.

First, the keys stick in the upright position until the first time
you depress them.  Then they are fine for about 6 hours at which
point they are stuck again.  I've removed them all and cleaned and
regreased them.  Any clues as to what's happening?

Any good ways of cleaning the bus bars.  I've gone over them with
alcohol but nothing came off.  They're pretty bad.  I was thinking of
some 600 grit sandpaper and slightly burnishing them.

My real issue is the CV output.  It's fine up until the input to the
potted module on the circuit board.  It's a Dynamic Measurements Corp
148-130 module.  It's pulling the CV negative.  I've removed the
module and am running the CV straight from the input.  The keyboard
divider chain is working fine except there is no hold function for
the CV.  Funny, there is no gate input to this module so I don't know
how it's supposed to know when to hold the voltage.

Does anyone have schematics for this keyboard or any information on
the Dynamic Measurements Corp module?  It's got a date code of '74 on
the bottom.  I'm trying to unpot it but it's not going very well.

Thanks. - Dave

Dave,

As far as the keys sticking,  You should really check out this 
website:

http://pw1.netcom.com/~arcsound/

They sell the rubber bushings that fit inside the keys to stop them 
from sticking and put your keyboard action back to factory quality.  
I've done several of my keyboards and they are GREAT!!!  

Argghh!!! Don't use sandpaper on the bus-bars!!! They'll probably 
work for a while (maybe) & then get oxidised and then you are royally 
screwed!!!  I used the Radio Shack Component Cleaner ($10) and it 
seemed to do the trick.

Sorry, don't have the schematic for the KB, but there are a few 
places including the guy that seems to spend his life selling it on 
eBay!!!

Guv

--- In vintagesynthrepair@y..., "djbrow54" <davebr@e...> wrote:
> I'm trying to restore an Arp 3604 keyboard.  Several questions.
> 
> First, the keys stick in the upright position until the first time
> you depress them.  Then they are fine for about 6 hours at which
> point they are stuck again.  I've removed them all and cleaned and
> regreased them.  Any clues as to what's happening?
> 
> Any good ways of cleaning the bus bars.  I've gone over them with
> alcohol but nothing came off.  They're pretty bad.  I was thinking 
of
> some 600 grit sandpaper and slightly burnishing them.
> 
> My real issue is the CV output.  It's fine up until the input to the
> potted module on the circuit board.  It's a Dynamic Measurements 
Corp
> 148-130 module.  It's pulling the CV negative.  I've removed the
> module and am running the CV straight from the input.  The keyboard
> divider chain is working fine except there is no hold function for
> the CV.  Funny, there is no gate input to this module so I don't 
know
> how it's supposed to know when to hold the voltage.
> 
> Does anyone have schematics for this keyboard or any information on
> the Dynamic Measurements Corp module?  It's got a date code of '74 
on

> the bottom.  I'm trying to unpot it but it's not going very well.
> 
> Thanks. - Dave

Yep,  they use the P.R.  

Did it to my 3604.  The keys were sticking on that too!!!

Guv


--- In vintagesynthrepair@y..., mtcasino@c... wrote:
> Dave:
> 
> I don't know if the Arp 3604 keyboard uses Pratt-Read Bushing, but 
they worked on my Odyssey just fine.
> 
> Mike Casino
>   ----- Original Message ----- 
>   From: djbrow54 
>   To: vintagesynthrepair@y... 
>   Sent: Saturday, July 27, 2002 11:31 PM
>   Subject: [vintagesynthrepair] Help - ARP 3604 Keyboard
> 
> 
>   I'm trying to restore an Arp 3604 keyboard.  Several questions.
> 
>   First, the keys stick in the upright position until the first time
>   you depress them.  Then they are fine for about 6 hours at which
>   point they are stuck again.  I've removed them all and cleaned and
>   regreased them.  Any clues as to what's happening?
> 
>   Any good ways of cleaning the bus bars.  I've gone over them with
>   alcohol but nothing came off.  They're pretty bad.  I was 
thinking of
>   some 600 grit sandpaper and slightly burnishing them.
> 
>   My real issue is the CV output.  It's fine up until the input to 
the
>   potted module on the circuit board.  It's a Dynamic Measurements 
Corp
>   148-130 module.  It's pulling the CV negative.  I've removed the
>   module and am running the CV straight from the input.  The 
keyboard
>   divider chain is working fine except there is no hold function for
>   the CV.  Funny, there is no gate input to this module so I don't 
know
>   how it's supposed to know when to hold the voltage.
> 
>   Does anyone have schematics for this keyboard or any information 
on
>   the Dynamic Measurements Corp module?  It's got a date code 
of '74 on
>   the bottom.  I'm trying to unpot it but it's not going very well.
> 
>   Thanks. - Dave
> 
> 
>         Yahoo! Groups Sponsor 
>               ADVERTISEMENT
>              
>        
> 
>   To unsubscribe from this group, send an email to:
>   vintagesynthrepair-unsubscribe@e...
> 
> 
> 
>   Your use of Yahoo! Groups is subject to the Yahoo! Terms of 
Service.

Thanks.  That's it.  I never thought about the bushings sticking to the keys in the 'up' position. - Dave

--- In vintagesynthrepair@y..., "kanaguvnor" <guvnor@r...> wrote:

> Yep,  they use the P.R.  
> 
> Did it to my 3604.  The keys were sticking on that too!!!
> 
> Guv
> Service.

Thanks for everyone's help on this.  I've figured out the connector and everything works except the S&H module.  I gave up on ever trying to find another or de-pot it to troubleshoot it.  I just designed a new module with a National LM398A S&H chip and built it on a small board with pins to fit in the original location.  I had to fly the CV output and a Gate input to the board.  Works great.  Now I'm waiting for the new bushings from Arcsound.  Should have this thing put back together and functional.  Thanks again for all the suggestions.

Dave

--- In vintagesynthrepair@y..., "djbrow54" <davebr@e...> wrote:

> My real issue is the CV output.  It's fine up until the input to the
> potted module on the circuit board.  It's a Dynamic Measurements Corp
> 148-130 module.  It's pulling the CV negative.  I've removed the
> module and am running the CV straight from the input.  The keyboard
> divider chain is working fine except there is no hold function for
> the CV.  Funny, there is no gate input to this module so I don't know
> how it's supposed to know when to hold the voltage.
> 
> Does anyone have schematics for this keyboard or any information on
> the Dynamic Measurements Corp module?  It's got a date code of '74 on
> the bottom.  I'm trying to unpot it but it's not going very well.