Film-Tech Forum ARCHIVE: CP65 Buzzing question

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Posted by Frank Dubrois (Member # 3042) on 03-16-2007, 12:16 PM:

We have a Dolby CP65 that puts out an occasional buzzing noise in the speakers (I think its just the front, but that isnt verified). When the 3 Cat 64B cards are removed and reseated, the noise goes away...for a while. Eventually it comes back and the proceedure is repeated. For now, it is being played in bypass. My question is, does it sound like the cards are defective since reseating them seems to fix the problem for a while? I haven't been told exactly where the noise is coming from because it cant be reproduced when I'm there and I don't want to just order 3 new Cat. 64B cards if thats not the problem. I'm just curious if anyone else has had this issue? I'm simply not familiar enough with the CP65 at this point. I just find it interesting that removing these 3 cards, and simply reseating them cures this problem for a while.

Thanks for any help.

Posted by Michael Schaffer (Member # 1204) on 03-16-2007, 05:10 PM:

Try removing them one at a time to see if the buzz is coming from just one of them. It could also be the power supply, but then it would be more likely to affect all three cards at the same time. If you have another unit that you can swap the power supply with, try that as well.

Posted by Frank Dubrois (Member # 3042) on 03-16-2007, 08:04 PM:

Well, is it safe to remove those cards while the processor is on? If we turn it off and remove a card, I beleive the noise will go away upon powering up...I don't know first hand, and I'm never there when it acts up.

Posted by Louis Bornwasser (Member # 3063) on 03-17-2007, 05:42 AM:

This type of problem is hard to find....unless you have a second cp-65. Mark the cards as to which processor and then swap TWO at a time until you get the symptom to move. Presumably the set up is similar between the two and the momentary un-tuning will be tolerable. Louis

Posted by Frank Dubrois (Member # 3042) on 03-17-2007, 03:06 PM:

Unfortunately, we only have one.

Posted by Michael Schaffer (Member # 1204) on 03-17-2007, 07:52 PM:

Have you tried to check on the monitor if the buzz comes from only one channel, and if so, which?
How frequently does the buzz occur? Does it come back "reliably" after a short while or is it just once in a while, after a long day of playing, or just after a few days (unlikely since I guess you power done the processor at the end of the day).
I would not pull out the cards while the processor is on. The voltages are low, but the circuitry is fairly senstive.
I think it is most likely that the problem is in the power supply. Maybe your dealer can organize a repair/exchange for you. If you put in the exchange power supply and the problem is still there, often they will allow you to return it back and get credit. They do understand that it is very hard sometimes to catch intermediate problems. If it is the power supply, you will only pay a small price for having solved this annoying problem (probably not more or much more than $300, but I have no idea about current r/e pricing for this item).

Posted by Kevin Raisler (Member # 1761) on 03-17-2007, 11:20 PM:

quote: Frank Dubrois
cards are removed and reseated, the noise goes away

I won't pretend to be an expert but I had this once with a cp 500 and it was in the backplane.

Posted by Monte L Fullmer (Member # 2797) on 03-17-2007, 11:27 PM:

quote: Kevin Raisler
with a cp 500 and it was in the backplane.

...and I had three CP500's do the same - bad backplane and replaced them to cure the situation after I traded cards from one processor to the other to see if the problem travelled.

But, it could be a PS acting up as well ..

Posted by Frank Dubrois (Member # 3042) on 03-18-2007, 12:19 AM:

Well, if it was the PS, I thought maybe other things might be acting up. I hope its not the backplane. I replaced one of those, and its a pain in the ass.

Posted by Monte L Fullmer (Member # 2797) on 03-18-2007, 02:31 AM:

quote: Frank Dubrois
I hope its not the backplane. I replaced one of those, and its a pain in the ass.

..when mine went, all I did was replaced the entire cases(taking out the cards, misc and removing the door..) that way it was a sinch to do the changeout - not removing just the backplane from the case...which then can be a pain ....