Film-Tech Forum ARCHIVE: USL power supply noise

This is topic USL power supply noise in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Michael Schaffer (Member # 1204) on 02-17-2004, 01:44 AM:

I copied this here from the DTS thread because it is really an altogether different subject:

What are the exact symptoms for the bad power backup switch? In our case, the processor sometimes (every other couple of days) produces a very loud hum and the signal LEDs on the noise reduction card go all the way up. After checking that the optical preamplifier was OK (and it does it in all formats anyway), I swapped power supplies and also the noise reduction card across 3 cinemas to isolate the bad component.
It turned out that the loud hum followed the power supply. It usually goes away after resetting the processor. Can this be caused by a bad backup power switch?

Posted by Mark Gulbrandsen (Member # 72) on 02-17-2004, 08:35 AM:

Michael, I would start by removing the backup power switch thats on the supply. Failure of this switch is usually indicated by one of the rail LED's going out and back on.... New or factory rebuilt units come without this unreliable switch anyway.
After you remove it jumper the two sets of solder pads that are closest to the front of the supply...as though the switch were in its normally out position. If this does not cure it then I suspect a bad regulator...also easy to replace. If it were on my service route I'd replace all rectifiers, caps and both regulators...basically rebuild the entire supply. An alternate route would be to do an R/A for a factory repaired unit. But its lots cheaper to do it yourself. BTW: Purchase at least 85 degc. or better caps....preferably 105 deg c. rated caps as they are getting quite common and will last longer.

Mark @ CLACO

Posted by Ken Layton (Member # 133) on 02-17-2004, 10:13 AM:

I agree about taking out that very troublesome switch. Also take a gander at the pc board for bad solder joints.