Samsung HPT4254X BN44-00161A P.S.Dead

[MagicSmoke]

Re: Samsung HPT4254X BN44-00161A P.S.Dead

Data sheet on 13N50CF here


N channel mosfet. If its showing shorted you will have to remove to test it. It could be something else in that circuit shorted.

[nogger]

Re: Samsung HPT4254X BN44-00161A P.S.Dead

I repair quite a lot of these PSU's. The QX801 & 802 are Mosfets & their operation is critical to this PSU powering up. They are in the Va voltage section & generate approx 63 Volts DC at the output plus all the smaller voltages like 12v 5v & 18 v will only be present if the Va tract is working so this is where you must concentrate your faultfinding.

First of all pop your meter across the outside pins of both QX801 & 802 (Gate to Source). You should have a reading of approx 10 ohms on each transistor. If the reading is way higher then you need to remove these FET's & measure again on the board. If still higher then the small surface mount diodes & resistors have been blown open.

The most likely (& most common) reason for the PSU failure in the first place is poor soldered joints around the FET pins, they make & break & eventually blow the FET's & SM components. Also check that the fuse next to the daughter boards is still intact & don't worry about the Vs voltage (Vs tract) for now because until you sort out the Va you wont get the Vs as the PSU will just keep shutting down

Check these readings & let us know what you have.

Graham

[ironman3452]

Re: Samsung HPT4254X BN44-00161A P.S.Dead

ok so new to here, Samsung 42" dead power board, opened it and found that the transistor QX801 and QX802 were blown, could badly make out the type, any ideas as to why they blew? have ordered a repair kit, but would like to know what would have caused them to blow.

[budm]

Re: Samsung HPT4254X BN44-00161A P.S.Dead

Are we talking about the exact same board BN44-00161A?

[ironman3452]

Re: Samsung HPT4254X BN44-00161A P.S.Dead

hey nogger, mine were blown apart so is there any way that you might know why this happened, could it be from a power serge, or something else?

[ironman3452]

Re: Samsung HPT4254X BN44-00161A P.S.Dead

yes this is the same board BN4400161A

[ironman3452]

Re: Samsung HPT4254X BN44-00161A P.S.Dead

ok so I have replaced all the bad caps, transistors, that were blown, also bought the repair package and installed all the components per guide, still clicks, checked relays to see if the contacts were ok, I have voltage until the relay opens, so now what?

[ironman3452]

Re: Samsung HPT4254X BN44-00161A P.S.Dead

so it seems like this is a standard problem with these sets, all I know is on mine it was not just caps, I guess I will be looking for a replacement board, any one here have a spare one for a low cost, let me know, thanks

[ironman3452]

Re: Samsung HPT4254X BN44-00161A P.S.Dead

so no reply, it is easy to repair bad caps, but try to troubleshoot other problems, I guess no one here knows how to do that, thought this was a site that you could come for help, guessed wrong, any one can soldier a pin on a board, but try to find real problems good luck, I will be leaving this forum, bye and best of luck on helping any one with this problem

[tw2005]

Re: Samsung HPT4254X BN44-00161A P.S.Dead

so no reply, it is easy to repair bad caps, but try to troubleshoot other problems, I guess no one here knows how to do that, thought this was a site that you could come for help, guessed wrong, any one can soldier a pin on a board, but try to find real problems good luck, I will be leaving this forum, bye and best of luck on helping any one with this problem

If the PSU powers up and voltages are correct you may very well have other issues like bad buffers and ymain. The logic board will shut the PSu down if a fault is detected.
Also these boards are notorious for cracked solders on the heatsinked FETs which can cause them to just shutdown or just click eventually powering up. there's 2 sets of fets that go, 1 for Vs and the other for Va voltages