Panasonic DVD Switching PS schematic/help

[Nathan Gregory]

I have a lot of experience repairing electronics gear, but this one has me
stumped. Maybe someone here can give me a hint.

I have a Panasonic DVD-RV31 DVD player with power supply problems. It's a
classic Switching PS startup glitch.

I have been unable to find a schematic, but I downloaded Sam Goldwasser's
excellent VCR PS schematic, and it is fairly close. I have spent hours
drawing my own PS schematic, and almost have it, except there are some IC's
I can't identify.

The Supply is dead, except for about 4V floating about on one secondary
winding. Several times while troubleshooting, it has suddenly started up,
after which it works perfectly until the AC line is unplugged. I've never
figured out what I did that starts it.

I know from experience these sorts of problems are usually due to a degraded
electrolytic, but I have painstakenly tested or replaced every electrolytic
capacitor in anything I can identify as part of the startup circuit to no
avail. I have also checked all the diodes and inductors, and even checked a
number of tiny surface-mount resistors. Nothing was bad, leaky or out of
tolerance insofar as I could tell and nothing I replaced improved operation.

Anyone have any clue what else I can look at? Any hints or suggestions at
all are welcome.

Regards,
Nathan

 

[Franc Zabkar]

On Wed, 7 Apr 2004 17:16:10 -0700, "Nathan Gregory"
<ngregory@deco-group-partners.com> put finger to keyboard and
composed:

I have a lot of experience repairing electronics gear, but this one has me
stumped. Maybe someone here can give me a hint.

I have a Panasonic DVD-RV31 DVD player with power supply problems. It's a
classic Switching PS startup glitch.

I have been unable to find a schematic, but I downloaded Sam Goldwasser's
excellent VCR PS schematic, and it is fairly close. I have spent hours
drawing my own PS schematic, and almost have it, except there are some IC's
I can't identify.

The Supply is dead, except for about 4V floating about on one secondary
winding. Several times while troubleshooting, it has suddenly started up,
after which it works perfectly until the AC line is unplugged. I've never
figured out what I did that starts it.

Assuming your SMPS is a classic design, check the "startup" resistor
feeding the gate or base of the chopper transistor. It often goes
open. Its typical value would be of the order of 100K or more.

I know from experience these sorts of problems are usually due to a degraded
electrolytic, but I have painstakenly tested or replaced every electrolytic
capacitor in anything I can identify as part of the startup circuit to no
avail. I have also checked all the diodes and inductors, and even checked a
number of tiny surface-mount resistors. Nothing was bad, leaky or out of
tolerance insofar as I could tell and nothing I replaced improved operation.

Anyone have any clue what else I can look at? Any hints or suggestions at
all are welcome.

Regards,
Nathan

- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

 

[Max Harding vk3jin]

have you tried the can of freeze and the heat gun?
"Franc Zabkar" <fzabkar@optussnet.com.au> wrote in message
news:ret9709a6nfet6s3t5uckecjtbkda2d82k@4ax.com...

On Wed, 7 Apr 2004 17:16:10 -0700, "Nathan Gregory"
ngregory@deco-group-partners.com> put finger to keyboard and
composed:

I have a lot of experience repairing electronics gear, but this one has
me
stumped. Maybe someone here can give me a hint.

I have a Panasonic DVD-RV31 DVD player with power supply problems. It's
a
classic Switching PS startup glitch.

I have been unable to find a schematic, but I downloaded Sam Goldwasser's
excellent VCR PS schematic, and it is fairly close. I have spent hours
drawing my own PS schematic, and almost have it, except there are some
IC's
I can't identify.

The Supply is dead, except for about 4V floating about on one secondary
winding. Several times while troubleshooting, it has suddenly started
up,
after which it works perfectly until the AC line is unplugged. I've
never
figured out what I did that starts it.

Assuming your SMPS is a classic design, check the "startup" resistor
feeding the gate or base of the chopper transistor. It often goes
open. Its typical value would be of the order of 100K or more.

I know from experience these sorts of problems are usually due to a
degraded
electrolytic, but I have painstakenly tested or replaced every
electrolytic
capacitor in anything I can identify as part of the startup circuit to no
avail. I have also checked all the diodes and inductors, and even
checked a
number of tiny surface-mount resistors. Nothing was bad, leaky or out of
tolerance insofar as I could tell and nothing I replaced improved
operation.

Anyone have any clue what else I can look at? Any hints or suggestions
at
all are welcome.

Regards,
Nathan



- Franc Zabkar
--
Please remove one 's' from my address when replying by email.