PSU Woes - Need Help!

[Darky8]

Hi Folks! I hope you can help me.

I'm not new to electrical work, but I am new to electronics. I seem to have reached the end of my somewhat limited knowledge with this PSU.

It's from a Panasonic WJ-HD316A Digital Recorder, which popped a few surface mounted fusible resistors (R101, R123) and a couple on another board. After replacing these fuses, the PSU now just cycles and as the protection circuit kicks in.

If I remove R101, the cycling stops and if I replace R101 but take away L101 it's also OK. So what ever it is within the IC101 area.

As far as I can tell all the components are ok (I have a really crap multimeter!), I have replaced SCR101, the capacitors marked 330 are ok (Checked ESR out of circuit), the diodes appear to do what they should etc

So I'm stuck and somewhat down hearted that I've managed to get this far, and yet have failed to make the thing work.

Any help would be gratefully received.

[stj]

Re: PSU Woes - Need Help!

see if any of the ceramic capacitors are shorted out.

[ben7]

Re: PSU Woes - Need Help!

The SCRs might be part of some "crowbar" circuit. I wonder if they are protecting (blowing the fuse(s)) the circuits down the line. Maybe one of the large ICs is bad?

[budm]

Re: PSU Woes - Need Help!

BTW, the original thread is here:
https://www.badcaps.net/forum/showthread.php?t=45537

[Darky8]

Re: PSU Woes - Need Help!

Once replaced, none of the fuses blew again.

[ben7]

Re: PSU Woes - Need Help!

Once replaced, none of the fuses blew again.

Hm? Once what was replaced? The SCRs?

[Darky8]

Re: PSU Woes - Need Help!

Thank you for your reply.

No, when I replaced the fuses. Both on this board were blown and one on another. They never blew again once replaced, it just cycles every second or so making the chirping noise.

[selldoor]

Re: PSU Woes - Need Help!

When it is cycling and chirping is it all connected up?

Have you tested the voltage each side of the fuses and worked across the board testing voltage at the inductors or the input output voltage on the ICs
Does the volatage vary with the on/off /chirp.
Can you pinpoint where the chirp is coming from.

[Darky8]

Re: PSU Woes - Need Help!

It does it with everything connected up and without anything connected. As long as the far left circuit is connected it freaks out.

Going to replace IC101 as I can't find anything else wrong.

[budm]

Re: PSU Woes - Need Help!

"It does it with everything connected up and without anything connected. As long as the far left circuit is connected it freaks out."
So the left circuit DOES NOT FREAK out when no load connected it? or as you said "It does it with everything connected up and without anything connected"

You should try using the resistors dummy load, the loads may have shorted circuits and cause the switching power supply to go into shutdown/re-start mode.
the board contain three switching power supplies.
https://www.badcaps.net/forum/showpo...90&postcount=8

[Darky8]

Re: PSU Woes - Need Help!

It's the left circuit that freaks it out. Disconnect the left circuit and half the machine runs ok. With nothing connected it's exactly the same, as soon as the left circuit is connected you can hear the PSU restarting.

I replaced the left circuit IC and it half ran for the first time with the left circuit connected. However, I think I noticed a small puff of smoke and now it's back to square one. It lasted about 2 mins.

I may just junk this PSU and fit it with an old ATX one.

Cheers

[Darky8]

Re: PSU Woes - Need Help!

It's all over, it went up in smoke so a complete failure :/

However, seeing the machine is PowerPC based it only requires the usual 3.3, 5, 12v. So I plan to use a small ATX PSU instead.

So I didn't win this time, hey ho on with the next dead thing!

Thanks for your help, I did learn something from all this but I'm not quite sure what.

Cheers!

[newtothis]

Re: PSU Woes - Need Help!

You learnt that when the Magic Smoke escapes things stop working? lol