Film-Tech Forum ARCHIVE: Question about the CP500 sound processor

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Posted by Todd Shelskt (Member # 4684) on 03-23-2008, 06:27 AM:

We're experiencing a problem with 2 of our CP500 units. When in the Dolby SR or A mode, we've lost sound and been unable get it back. Even the bypass doesn't work. It's an intermittent problem. We could be 2 hours into a movie and the sound suddenly goes out.

No problems when we're in the digital mode, but we play films from India which rely on optical tracks (or DTS, which we don't have).

Any suggestions?

Posted by Marin Zorica (Member # 1716) on 03-23-2008, 08:32 AM:

It's strange that doesn't sound when is in bypass. I think that problem occurs somewhere in optical preamp, because during digital is ok, and you said that is happend with 2 units....don't know which chance is to have cell and reader on projector problem in same time on different machines?

If you have more 500's try replace preamp with some other.

So....check wiring, check cell and led, or reverse scan if you have, and check reader supply if is reverse scan if you want to be 100% sure that's ok.

Posted by Mark Gulbrandsen (Member # 72) on 03-23-2008, 08:58 AM:

Check the power supply... I have lost a number of CP-500 supplies over the years. Power supplies were never Dolby's best feature..... Also....

If you happen to have Kelmar Red Reverse Scan analog readers then also check those power supplies as well. If you have the supply in the grey and white box it too will eventually fail. All of them do.

Mark

Posted by Louis Bornwasser (Member # 3063) on 03-23-2008, 10:56 AM:

I agree with Mark to check the Kelmar power supplies. I do want to clarify that the red LED will still light when the power to the preamp dies. (If that is the problem, you are not feeding audio so bypass does not help.)

Also, if you see discoloration on the multipin plug inside the power supply you are on the right track. So far, I have had 100% success resoldering the pins on the board and on the (hot) resistor located right next to it.

If not too far baked, you can consider this a permanent fix. The problem originated with improper solder techniques at the off-the-shelf vendor. Louis

Posted by Danial Simmonds (Member # 4638) on 03-23-2008, 11:01 AM:

Yup cant agree more, check the Power Supplies for the CP500 and LED's. But here in Malaysia most indian prints are like that, we use DTS because the analog most of the time is very soft.

Good Luck.

Posted by Pete Naples (Member # 761) on 03-23-2008, 02:11 PM:

Re: The bypass not working.
Stick a loop of Cat69T on and crash the CP500 into bypass, to see if bypass works at all. You'd be amazed at the number I've come across that are either not calibrated correctly for bypass, or don't have the bypass power supply connected.

Other than that, check the main PSU rails, don't rely on the indicator LEDs, the pre-amp, 222SR/A and CAT681 analogue switch card are all suspects. I concur with the comments made by my learned friends above;)

Posted by Todd Shelskt (Member # 4684) on 03-23-2008, 11:02 PM:

Thanks to all of you for your help. Film-Tech is awesome!