Polaroid DHM 0100 dvd player audio hum

Maybe they aren't at the same ground potential. I have problems with this in some of my older equipment with bad capacitors and the like in the power supplies. Or even bad caps driving the outputs if they aren't isolated correctly. If I'm in a hurry, I tie the chassis together and ground them. This can be a bad thing on some equipment though. In short, I'm suspecting bad caps somewhere.

I had been wondering if connecting a jumper between the grounding busses of both pieces of equipment would make any difference, both pieces of equipment have 2-wire power cords and were plugged into the same power strip; but, found a leaky cap before I tried anything else - it was rated 400vdc,

33microfarad (can't remember how to call up one of those mu-thingies).

This brings on another question, though I realize without schematics to refer to, any answer will be a generality. This dvd player is very basic, just plays dvds, and cds of standard or mp3 or photo-cd format, and has, besides the power button, 3 other buttons: open-close door, play-pause, and stop.

One can't select a track to play, or fast forward or any of that unless you've got the remote. The cap appears to be just before the input to an amplifier (an 8-pin dip chip), so it seems to me that a 400 v rated cap is rather excessive for the volts I'd expect going into that kind of circuitry.

Even if I'm wrong about what kind of circuitry this cap is feeding,

400 vdc seems like way more than would ever be encountered in a dvd player (it plugs into 120vac). So, just wondering if there's a good reason, other than 'that's probably what the manufacturer had on hand when they built the boards'.

It's not just idle curiosity, I replaced the cap with 2 caps in series, the rating of them each being 50 microfarads, 150vdc, as that was the closest thing I could find in my stash of scavenged parts.

Thanks for any info, Mike

Mike,

I just got done working on a couple mid-2000's DVD players, and have seen those 8-pin ICs in the power supplies. They aren't op-amps, they're switch-mode controllers, and also contain the power transistor/ FET that used to be a separate device in earlier designs. So, the high voltage off that cap does run thru that chip. I'd write down the numbers off that chip and save it in case it blows up and needs to be replaced. STMicroelectronics and Philips, among others, make those integrated SMPS chips, so should be available from places like Digi- Key or Mouser should the need arise.

That cap is the filter on the output of the bridge rectifier that connects to the AC line input. The power supply probably is a universal-input type, meaning it can run on 100 - 240 Vac. The 400 V cap is there in case you want to run your DVD player on 240 V. If you're in the US with 120 V power, you can get away with a 200 V cap in that application.

You should try to get the correct size cap, 33 - 47 uF, 200 - 400 V. With two 50 uF caps in series, you're only getting 25 uF of capacitance. The voltage will divide equally between the caps only if they have identical leakage currents, which doesn't always happen in practice. That cap has rectified AC from the power input across it whenever the DVD player is plugged in - you don't want one of your caps going Bang in the middle of the night...

Thanks for that bit of info, talk about an ill-informed guess on my part. I think I'll take the cover back off and start monitoring the circuit some, and be on the lookout for a closer matched cap. Thank you very much!

Mike