Vintage Synth Repair

Yes I've used HCT and in LS compatible situations..but im not looking for compatibility with LS this time..

Basically 74C is a cmos format with a 74 series pinout. So I guess looking at the readily available variations of the 74 series, HC would be ideal..maybe.



________________________________
From: arthurok <arthurok@...>
To: vintagesynthrepair@yahoogroups.com; Philip <eggwheatis@...>
Cc: vintagesynthrepair@yahoogroups.com
Sent: Mon, 28 June, 2010 21:08:10
Subject: Re: [vintagesynthrepair] Oberheim OB-X and Cmos 74 series + Autotune

 
what about  using 74hct  
ics    
amazingly  4000 series  cmos ics  
are still  in  production
im not  sure 
about    small  scale  bipolar digital  
ics
74hct  is supposed  to  be  
fully  compatible  with  74ls   parts
"im  not  sure about   
leaving  unused  inputs  floating
thats  a  big  no  -  
no   when using    cmos parts    
someengineers   even   
pulled  up   unused  ttl   
inputs    using a resistor to  vcc
to  protect the  input  from  
powersupply   overshoot.
----- Original Message ----- 
>From: Roger J 
>To: Philip 
>Cc: vintagesynthrepair@yahoogroups.com 
>Sent: Monday, June 28, 2010 12:30 
>PM
>Subject: Re: [vintagesynthrepair] 
>  Oberheim OB-X and Cmos 74 series + Autotune
>
> 
>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@yahoo. com>
>To: >  winking_n_nodding@ yahoo.com
>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@ yahoo.com>
>To: >  vintagesynthrepair@ yahoogroups. com; GB 
>  <grantbt@jps. net>
>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.
>>
>
>
>
>
>