Vintage Synth Repair

There was an engineering change order/service bulletin that removed the newer series CMOS 74C part and replaced it with the older TTL 74 series part due to a fan out issue on the OB-8(or was it the OBXa) in the panel circuit. 

Only reason I mention it is that you could be "updating" but adding a problem. Just something to keep in mind. I am sure some of the guys will pipe up on the details that are a bit foggy in my brain this Monday.
R


________________________________
From: Philip <eggwheatis@...>
To: winking_n_nodding@...
Cc: vintagesynthrepair@yahoogroups.com
Sent: Sun, June 27, 2010 12:53:26 PM
Subject: Re: [vintagesynthrepair] Oberheim OB-X and Cmos 74 series + Autotune


Yes as I've discovered...well as soon as I saw all those molex pins I knew there would be trouble.. I re-soldered about twenty cracked joints..
 
I basically completely stripped it, re-soldered, re-capped..then started going through all the logic faults.




________________________________
 From: Roger J <winking_n_nodding@...>
To: vintagesynthrepair@yahoogroups.com; GB <grantbt@...>
Cc: vintagesynthrepair@yahoogroups.com
Sent: Sun, 27 June, 2010 19:10:02
Subject: Re: [vintagesynthrepair] Oberheim OB-X and Cmos 74 series + Autotune

 
Most OBX have solder faults between the CPU board and the voice cards. So start there and re-solder all first. You may be surprised how many other problems are resolved. 

R

rom: Philip <eggwheatis@yahoo. com>

To: GB <grantbt@jps. net>
Cc: vintagesynthrepair@ yahoogroups. com
Sent: Sun, June 27, 2010 10:23:13 AM
Subject: Re: [vintagesynthrepair ] Oberheim OB-X and Cmos 74 series + Autotune

  
Thanks, I'd like to find new equivalents if possible..I find those old CMOS ic's to be inherently flaky...so anyway I've gone for new 40174's as I need at least two to get the controls working properly again..




________________________________
 From: GB <grantbt@jps. net>
To: eggwheatis@yahoo. com
Cc: vintagesynthrepair@ yahoogroups. com
Sent: Sun, 27 June, 2010 17:55:51
Subject: Re: [vintagesynthrepair ] Oberheim OB-X and Cmos 74 series + Autotune

 
We have a bunch of "new" 74C at my work. They are still in the original rails, but were bought many years ago. If you give me a list of what you need. I can see what we have. Also, the sockets can get dirty, so sometimes even reseating the chips helps  or replacing the sockets with new double-wiping ones.
 
GB
 
----- Original Message ----- 
>From: Philip 
>To: vintagesynthrepair@ yahoogroups. com 
>Sent: Sunday, June 27, 2010 9:46 AM
>Subject: [vintagesynthrepair ] Oberheim OB-X and Cmos 74 series + Autotune
>
>  
>Hi, I'm repairing a hopelessly faulty OB-X...I'm dealing with all the CPU and digital control side first....all the voice board faults secondly.. 
>
>
>
>First question...it' s packed with early cmos 74 series IE 74C174 etc...what are the best equivalents for these and other 74C types? 74HC? 40174 for example?
>
>
>Second question: How long is the Autotune function supposed to run for? At the moment it stays on for about 2 seconds after button press...not that it seems to do much as it's hopelessly out of tune with various boards missing a VCO here and there...
>
>
>Thanks, Philip.
>