OT: new info on fuse

From: Chad Fernandez <fernande_at_internet1.net>
Date: Sun Dec 28 23:01:42 2003

Tony,

I pulled the power supply from the laserdisc player. I couldn't see it
adiquately in the machine.

Tony Duell wrote:
> Can you tell us a little about the PSU design? Is it a 'linear' PSU, with
> an iron-cored mains-frequecy transformer? Or a switcher, with HV
> capacitors (look for a couple rated at 200V each) and a chopper transistor?

I find one cylindrical cap that is 200v and 220uf and one 250v .1uf cap
that looks like a chicklet (kind of chewing gum). I don't have any idea
how to identify a chopper transistor..... could that possibly be labeled
"Q1" and have a heat sink on it? I also see a couple transformers and a
bunch of resistors an IC and assume most of the D#'s are diodes. There
are quire a few "Q#" labeled items too.

This power supply does smell a little like something let the magic smoke
out.


>
> If the former, can you disconnect the secondary windings of the
> transformer from the PCB? If you can, then try a new fuse with the
> windings disconnected. If that blows, then you have shorted turns in the
> transformer, or a short in some component on the mains input side (RF
> filter capacitor?).
>
> If it's a switcher, then you have fun (for suitable values of 'fun'. You
> need to check forwards from the mains input and at least find the mains
> rectifier diodes and the chopper transistor. Check these for shorts. If
> the transistor is OK, and one or more of the diodes is shorted, then
> replace the diodes (use something rated at _at least_ 400V 2A) and try
> again. If the chopper is shorted, well, you've probably got other
> problems too, and _I_ wouldn't want to do much more without a schematic...

How would I check the rectifier diodes and the chopper transistor for
shorts? Check for continuity with ground on each pin?

Chad Fernandez
Michigan, USA
Received on Sun Dec 28 2003 - 23:01:42 GMT