Dead AUX winding on Samsung BN44-00259 PSU ?

[Dannyx]

Re: Dead AUX winding on Samsung BN44-00259 PSU ?

One trick is to make the aux. voltage using batteries, a couple 9V with series diodes from the junkbox to get down to say 16V or above the UVLO. Sometimes 18V is fine.
This allows the (standby) SMPS IC to stay running.
The batteries are floating at hazardous live potential, but at least voltage measurements can be made.

Because the SMPS IC has (battery) power before mains is applied, soft-start sequence is expired but nothing has blown up yet when I do this.

I wonder if your snubber is working, since the multimeter on the drain adds capacitance to that.

I was thinking just that: somehow simulating VCC to trick the IC into staying on. Sadly, I have no place of getting 18v from the board itself - I have to do it "externally". I was thinking of using a separate supply (like a small lab bench supply which I have) to do that, though it's likely something will go bang if I apply its output to DM802 (disconnected from RM890 of course, so it doesn't flow back into the transformer) and its GND to primary ground of the PSU, so I'm a bit reluctant to try it. About the snubber (despite already swapping CM805 with the one from the working board >_>): I see there's actually a spot for where a CM806 should go, though it's missing and says N.C there. I actually tried installing one, thinking it would do what the meter does (allow just enough current to flow through the transformer to excite the AUX winding too), but not knowing what value it should have, I just chose a random one, can't even remember the value right now. It didn't have any nasty effects, but didn't make a difference either: I still had to touch my meter probes to it to get it going and it didn't resume after a shutdown...

[gabiz_ro]

Re: Dead AUX winding on Samsung BN44-00259 PSU ?

On few cases,don't remember what IC was,similar action,measurement of voltage even in one case just touch with probe on GND and IC start,problem was solved by changing IC.
Take note that even IC is brand new may not be OK.

Could be some PCB problem.

On another one working,swap one by one and test after each step.
If in the end you swap all of them from defective one to working one and still no go,maybe some tracks damaged,PCB burned and may have resistance.

Swap only what is related to that IC not all on board.

[Dannyx]

Re: Dead AUX winding on Samsung BN44-00259 PSU ?

If you read further down, I did mention some traces and/or pads falling apart, which should come as no surprise after so many rounds of soldering, so I rebuilt them using wire like you see in the pictures: notice how the jumper wire which normally connects the two D pins of UM801s has no pad left around it so I twisted some solid core wire, tinned it and wrapped it around the said pin....the board falling apart like this further makes the job of testing stuff more annoying....

[gabiz_ro]

Re: Dead AUX winding on Samsung BN44-00259 PSU ?

Try to make as much possible in original config.
No inductors bypassed by wire.
Clean PCB.
Looks pretty bad.

[Dannyx]

Re: Dead AUX winding on Samsung BN44-00259 PSU ?

Try to make as much possible in original config.
No inductors bypassed by wire.
Clean PCB.
Looks pretty bad.

I know it looks terrible and the light only enhances the crud that covers the board Those aren't really inductors, they're ferrite beads used to suppress the high frequency noise around those jumper wires, though they might have some funny side-effect....it doesn't explain why the PSU didn't fire right up when I put in the "new" UM801s, since the board was intact at that point. I have cleaned it up a bit since then, though I won't be able to make the connections without some of those jumpers because some of the pads are no longer there.