Film-Tech Forum ARCHIVE: Dolby CP-50 Switch Card with non-sync distortion

This is topic Dolby CP-50 Switch Card with non-sync distortion in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=004698

Posted by Matt Close (Member # 996) on 03-23-2003, 06:24 PM:

I have a Dolby CP-50 with a switch card that is distorting the left channel when in non-sync music mode.... When I say distorting, I don't mean an 'over-driven' type of distortion.... I mean 'an amp running on too lower voltage' kind of sound. The problem is most definitly with the card as I have ruled out all other options. I just wanted to know if anyone else had ever had this happen with a CP-50, and could lead me to the fault quicker.... Which IC's, caps to look at?

Posted by Rick Long Jr (Member # 541) on 03-23-2003, 07:38 PM:

What switch card are you using? The 112, 113 or 113C? The 112 and 113 just routed the signal straight in and out through the relay on the card. It didn't go through any of the other cards, Which is why the fader did not affect the nonsync. The 113C had a nonsync level control onboard, but I don't think it had much else that would affect it either. I have had relay problems with the older cards though.

Posted by Matt Close (Member # 996) on 03-23-2003, 08:11 PM:

Sorry ... my bad ..... It's a 113C. The one with the fader control on the front of the card.

Posted by Scott Norwood (Member # 30) on 03-23-2003, 10:00 PM:

I've seen something similar with one cat. 113C card (no sound in L and R channels in non-sync; C and S were fine). Replacing the card with at cat. 112 or another cat. 113C would fix the problem.

Posted by Matt Close (Member # 996) on 03-23-2003, 11:51 PM:

No doubt it would .... as I am sure the problem is with the card's pre-amp for the non-sync. What I am hoping is that someone knows off hand, just which IC's or caps I should look at first.

Posted by Marc Jones (Member # 29) on 03-24-2003, 11:45 AM:

There is a general ciruit diagram in the CAT113 C manual
Looks like IC 107 would be a possible source of your problem
or IC 108 ? (hard to tell the number) if you follow the left channel out that would be your next chip.
Hope this helps