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]

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

 

[Max Harding vk3jin]

have you tried the can of freeze and the heat gun?

 

[Shoreline Electronics]

Schematic sent to your email.


--
==========================
Jeff Stielau
Shoreline Electronics Repair
344 East Main Street
Clinton,CT 06413
860-399-1861
860-664-3535 (fax)
[email protected]
========================
"If you push something hard enough it will fall over."
Fudd's First Law of Opposition - Sir Sidney Fudd

 

[Nathan Gregory]

Thank you sir. You have been a big help. While the schematic
was not exact, is was good enough to get me in the right place, and
when I did, I found R1042, supposed to be 470k, was in fact over 800k.

I replaced it and the player is back in service, working as it's
supposed to.

Much appreciated.

Nathan

 

[Nathan Gregory]

You nailed it Frank. It was R1042, 470k, increased to over 800k.

I replaced it and all is well. My profuse thanks to all on the
net who gave me a helping hand. I hope someone else will find this
thread and solve their own similar problem.

Thanks to all,

Nathan