Samsung HP-S4253 Power supply repair

[cedward138]

Hi all,
I need help repairing psu (BN96-03252A). The tv just did not power up one day although there have been a few instances where i've had to fiddle with the power button to get it to start.

Examination of the board showed a small area of discoloration and the resistor (R455-1) there was found to have come unsoldered. Re-soldering did not bring the unit back to life.

Just did another examination and found a component (U404) which has also worked loose.

The large capacitors show a funny pattern as far as the solder on the leads but i'm not sure that it's dry joints.

Please look at the attached pictures and advise as to possible steps to revive the board.

[stj]

Re: Samsung HP-S4253 Power supply repair

the big caps are soldered through rivets to make the joint stronger.

[cedward138]

Re: Samsung HP-S4253 Power supply repair

Any ideas Tom66?

[selldoor]

Re: Samsung HP-S4253 Power supply repair

Picture of the full board is not clear enough for trouble shooting.
Check over and resolder any suspect joints.
What voltage do you get at the main cap. CARE I am going to assume you know what you are doing if not - ask.
What secondary voltages do you get at the connector to the main board.
Checked ALL fuses.
Read the 4 stickies at the beginning of this thread?
Thoroughly tested the switch for operation and continuity to the main board?

[cedward138]

Re: Samsung HP-S4253 Power supply repair

Truth is I don't really know what i'm doing. I have rudimentary electrical/electronic skills, so I can follow if given the guidance.
Did visual inspection but not voltage measurements (DMM is available)
I will resolder the loose component U404 (voltage regulator?)
Fuses on the power supply checked ok.
Switches, cords etc are ok as tv works by swapping board from identical tv which has some issue with Y-main board. (For a separate thread)
Will try to get better focused picture of whole board or maybe take it in halves. Will post after reading stickies

[cedward138]

Re: Samsung HP-S4253 Power supply repair

Read quite a bit on Badcaps.net as well as other sites online.
Was not able to get detailed picture of whole board so took shots in sections.
I resoldered the voltage regulator. No other components appeared suspect either in shape, color or attachment.

Decided to first check for pson voltage before jumping it to ground to check for other voltages. While probing the pson pin, i noticed a brown ooze flowing below two transformers on the board.(seems to be the green one but not sure)
After quickly disconnecting mains, also noticed 1 of $ large caps had also oozed. There were no buzzing or popping sounds or any smells emitted.
The first 6 pictures are before connection with the last 3 showing the ooze afterwards.

Is the board trashed?

[stj]

Re: Samsung HP-S4253 Power supply repair

i'd like to say that's glue, but i'm not sure about it's placement.
i can say it's NOT leakage from anything.

is it dry?
you want to try to scrape it off because it can get conductive and short stuff out.

[cedward138]

Re: Samsung HP-S4253 Power supply repair

Definitely not glue. Look at the corresponding sections of the board before powering up (images 2 and 4 vs 8 and 7) and its not there.
Was flowing like thick liquid which I mopped some up with a q-tip to sniff for odor.

[stj]

Re: Samsung HP-S4253 Power supply repair

btw, did you check the 4+ fuses?

[stj]

Re: Samsung HP-S4253 Power supply repair

that "stuff" looks like it was spilled over the board btw.
who was near it other than you?

if you powered up in the tv, could it have come from another board?

[cedward138]

Re: Samsung HP-S4253 Power supply repair

It was on the table with no one else close by having warned them of dangerous voltages.
The tv is at another location altogether

[cedward138]

Re: Samsung HP-S4253 Power supply repair

Regarding the fuses, the psu has 2 and they tested ok before and after the ooze.
There are fuses on the otter boards but not related to this "incident"

[stj]

Re: Samsung HP-S4253 Power supply repair

no, there are atleast 4.
look at the light-brown cylinders marked F10x on the board.

[cedward138]

Re: Samsung HP-S4253 Power supply repair

Did not recognize those were fuses at first blush.
There are 3 such in addition to the 2 white ceramic ones. All 3 tested as ok.

[selldoor]

Re: Samsung HP-S4253 Power supply repair

Well that is really strange - the big cap could have oozed - take it out and clean it up with IPA. The stain between the transformers is odd as there is nothing that could have oozed.

Anything showing on the back of the board and it is on a non conductive surface?

[Alastair E]

Re: Samsung HP-S4253 Power supply repair

Looks like the cat puked on it to me, that 'stuff' isnt on the board--in two different locations--earlier pictures....

[cedward138]

Re: Samsung HP-S4253 Power supply repair

The plastic separator feet are still attached to the board so that kept the pcb itself approx 1 cm from the table top which is MDF at any rate.
There are no signs on the back of the board after the incident.

There are no cats or other pets here and at any rate I never left after plugging the ps.
Is there any dielectric in the windings of those transformers?

[johnboy1313]

Re: Samsung HP-S4253 Power supply repair

Did you see the cap pop and start oozing or did you suddenly notice stuff on the board? I suppose it's possible that the big cap popped with enough force to project some of it's contents, which then landed on the board between the transformers.

[cedward138]

Re: Samsung HP-S4253 Power supply repair

Did not hear or see when the cap popped. Noticed the stuff by the transformers before the cap. Projection from the cap sounds plausible. The stuff was of the same color and consistency as that from the cap.

[selldoor]

Re: Samsung HP-S4253 Power supply repair

OK enough conjecture remove the big cap and then remove the black disk from the end. You will then be able to see if it has popped or not.