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From: mike on 15 Mar 2010 11:46
Hi,

I have a Polaroid DHM 0100 dvd player that has (what I think is 60
cycle) hum on the audio outputs, so am hoping for some pointers on how
I might solve the problem. As far as test equipment goes, I've got a
couple different DVM's, but no O-scope or ESR meter.

The hum is on both left and right channels when using RCA-type patch
cord, and a kind of odd thing about it is that when the player is
first hooked up but still off there's no hum from the player, but it
immediately is there when the player starts to play a CD - audio is
played but with annoying hum which varies with volume control. Then,
if the power to the player is shut off the audio hum is still there
unless the power to the player is unplugged - then the hum stops. I
think my patch cord is good, as I also used it with a CD player, which
plays fine on the same inputs to stereo.

Polaroid's website doesn't offer any support for them and there's not
much other helpful info on the web. I did find an owner's manual in
pdf to download, but no circuit schematics are included. The player
came with a remote but I don't know where it is, or I'd go into the
OSD and see if there's anything odd there.

Thanks in advance for any ideas or info.

Mike
From: Sansui Samari on 17 Mar 2010 06:20
On Mar 15, 8:46 am, mike <mlight...(a)survivormail.com> wrote:
> Hi,
>
> I have a Polaroid DHM 0100 dvd player that has (what I think is 60
> cycle) hum on the audio outputs, so am hoping for some pointers on how
> I might solve the problem.  As far as test equipment goes, I've got a
> couple different DVM's, but no O-scope or ESR meter.
>
> The hum is on both left and right channels when using RCA-type patch
> cord, and a kind of odd thing about it is that when the player is
> first hooked up but still off there's no hum from the player, but it
> immediately is there when the player starts to play a CD - audio is
> played but with annoying hum which varies with volume control. Then,
> if the power to the player is shut off the audio hum is still there
> unless the power to the player is unplugged - then the hum stops.  I
> think my patch cord is good, as I also used it with a CD player, which
> plays fine on the same inputs to stereo.
>
> Polaroid's  website doesn't offer any support for them and there's not
> much other helpful info on the web.  I did find an owner's manual in
> pdf to download, but no circuit schematics are included.  The player
> came with a remote but I don't know where it is, or I'd go into the
> OSD and see if there's anything odd there.
>
> Thanks in advance for any ideas or info.
>
> Mike

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.
From: mike on 17 Mar 2010 09:30


Sansui Samari wrote:


> 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



From: Mike WB2MEP on 18 Mar 2010 01:33
On Mar 17, 9:30 am, mike <mlight...(a)survivormail.com> wrote:
> Sansui Samari wrote:
> > 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...
From: mike on 18 Mar 2010 08:23


Mike WB2MEP wrote:
> On Mar 17, 9:30 am, mike <mlight...(a)survivormail.com> wrote:

> 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
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