Film-Tech Forum ARCHIVE: CP65 Audio Output problem

This is topic CP65 Audio Output problem in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by V.V.Tushit Vijay (Member # 5455) on 11-05-2010, 02:11 PM:

Hello ,
i had an Dolby CP65 removed from a theater. we purchased it . Today we made it to play. We noticed that LEFT channel of the processor is not working. I checked in all inputs the out put is not present. And the signal in CAT cards was found. And i changed CAT64B. But problem was same. Is there any solution for this . Can Any one Help me in this issue.

Posted by Steve Guttag (Member # 268) on 11-05-2010, 05:05 PM:

Check the three bypass relays on the rear.

Posted by V.V.Tushit Vijay (Member # 5455) on 11-05-2010, 06:07 PM:

Relays were checked . But same problem .

Posted by Sam D. Chavez (Member # 1841) on 11-05-2010, 06:31 PM:

I would check the output wiring to the left power amplifier is not short circuited.

Have you put the audio from the CP65 right output to the left power amplifier? I know this is very basic, but it is best to eliminate the simple possibilities first.

Posted by V.V.Tushit Vijay (Member # 5455) on 11-05-2010, 06:34 PM:

Given Correct outputs to the amplifier. Right Channel is working good but left one is not working

Posted by Steve Guttag (Member # 268) on 11-05-2010, 06:48 PM:

Put the unit into "bypass" and see if you have any signal there (on the offending channel).

Posted by Marco Giustini (Member # 4544) on 11-05-2010, 07:05 PM:

Do you mean that you can see the signal LEDs on cat. 242 and you still do not have signal at the output?

Posted by V.V.Tushit Vijay (Member # 5455) on 11-05-2010, 07:13 PM:

Yes.. We can see the signal present in 242 But there is no output.

Posted by Sam D. Chavez (Member # 1841) on 11-05-2010, 10:18 PM:

Yes, you can have a 242 green LED on the left channel and still no audio. The LEDs are before the switch on the 242 if I recall correctly.

As I said before, try feeding the right channel audio from the 65 which is known to be good into the left channel power amp. This will rule out a number of issues.

Steve's suggestion is good as well as it bypasses most of the 65 audio. But try my idea first.

Posted by V.V.Tushit Vijay (Member # 5455) on 11-06-2010, 12:38 AM:

We checked in bypass its working good . But in normal the audio is not working.

Posted by Steve Guttag (Member # 268) on 11-06-2010, 09:48 AM:

The LEDs are after the switch (think about it).

So, what is left is the Cat 64B, the VCA and the line driver on the output.

Put a meter with a suitable test signal (from a generator or program) on the (Left) test point of the Cat 242. This will see the signal before the line amp but AFTER the EQ and VCA (have the fader at "7"). Is the signal there?...if so, you are down the the last stage. If not, you are back up to the VCA.

Odds are though regardless of where you find the signal has vanished, it is likely a coupling capacitor that has opened up.

C124 couples the EQ to the VCA (1uF). C134 (2.2uF) couples the VCA to the Line Amp (and test point) and then C139 with C140 (100uF) couple the line amp to the output of the Cat 242.

I believe the 1uF and the 2.2uF are tantalums...my experience is that they tend to work or explode (violent failures)...the output caps, the 100uF are going to be electrolytics. They have a less than stellar service record on the long run (as a Category, not necessarily on the Cat 242). If you have signal on the test point...go straight for them, C139 and C140. I'm less inclined to suspect the VCA (it has L,C, R and S channels and I have not had one go bad on me yet) or the output op amp, Left and Center share the same one and the 5532 series has never failed me.

Note, if wire link W5 is missing...Left will play MUCH lower which may make it seem like it isn't working.

Of course, there is always the freak resistor that, for no reason, opens up too.

Steve

Posted by Sam D. Chavez (Member # 1841) on 11-06-2010, 09:57 AM:

Steve is correct. I meant to say the LEDs are after the switch but before the actual output stage.

Posted by Steve Guttag (Member # 268) on 11-09-2010, 04:51 PM:

I had a chance to look at the Cat 242 today...I would suspect the C139/C140 even more...they are located right behind the test points and can easily be grabbed when removing the card, possibly breaking the lead(s). Give them a look.

Steve