PN50A510P3FXZA Power Supply BN44--00222A

[kevinm34232]

TV would not power up, had only standby voltage. Found transistor QX807 was shorted (STS2N5H3LL):
http://www.mouser.com/ProductDetail/...G%2FV3BQ%3D%3D

Part was discontinued, I ordered (SI7892BDP-T1-E3)
http://www.mouser.com/Search/Product...I7892BDP-T1-E3

I tried matching up specs, but can someone more knowledgeable tell me if this is a suitable replacement??

[Nick's Tvs]

Re: PN50A510P3FXZA Power Supply BN44--00222A

A lot of the time you can call them directly as well as digikey and ask them if they have alternatives and they will help you with that type of info. They usually have a few tech guys on standby for more technical questions.

[flocko]

Re: PN50A510P3FXZA Power Supply BN44--00222A

Is the board showing a two blink alarm code for faulty 5.3v ?if one or other QX807/8 show as shorted .you will need to check or replace the buck controller as well L6725,although obsolete these parts can still be found,I keep a stock but am in the UK, the one that you list could well work but have not checked pin out .

[kevinm34232]

Re: PN50A510P3FXZA Power Supply BN44--00222A

Pin out matches..

Here's where I'm at, with X and Y Mains discod, when PS is plugged into A/C power I have only 5V standby. If I ground PS-ON (high when off, low when on), the relays will click but no other voltages come up.

Also if I apply 5.3V with my bench power supply to VS-ON, nothing changes except the 5.3V line comes up slightly to about 1.4V.

I found a schematic on Tom66's site for a substitute for this power board.



Anyone able to help me find where the problem is?? I have found no other obvious shorts on the big transistors..

[flocko]

Re: PN50A510P3FXZA Power Supply BN44--00222A

Disconnect all the plugs apart from mains in.With the mains on you should see the LED on the the alarm board come on, this shows you have 5v stby. Jump PSon to ground, do this by shorting JP154 (end jumper to the right of CN801 socket) to ground, you must leave this grounded ,this should bring in relays and low voltages to board,if the relay clicks in then out you can read the blink code on the alarm board,this gives you were the problem can be found,if you have the low voltages you can now with a 470-1k resistor short STby to VSon this will bring up the high VS voltage. there are no schematics for this board. please post your findings

[kevinm34232]

Re: PN50A510P3FXZA Power Supply BN44--00222A

I did this process, see above. When ground PS-ON, the relays click on but no other voltages come up..

The green LED lights up before and after PS-ON is grounded, but never blinks.

I believe the schematics above are for substitute board BN44-00237A and are similar or same..

I replaced QX807 with what I believe is a suitable replacement (see above) because it appeared to have G-S short. Before I did this, it would cycle PS on and off.

[flocko]

Re: PN50A510P3FXZA Power Supply BN44--00222A

the BN44-00237A are not the same or anything close as far as schematic go, but can be used as a sub.the relays click in and stay in all the time you ground PSon not drop out,what happens to the voltage on the main caps when the relay comes in(PFC)

[kevinm34232]

Re: PN50A510P3FXZA Power Supply BN44--00222A

Checking now... Can you verify that my QX807 is a good replacement (post 1)? The package/case is different but the pinout is same (SOIC-8/PowerPAK SO-8)

[kevinm34232]

Re: PN50A510P3FXZA Power Supply BN44--00222A

Looks like I'm not getting voltage at the large 450V caps before or after PS-ON, is that possible? I am testing at JP112 to left of large caps for hot + , and another spot I ohmed out for hot ground.

[flocko]

Re: PN50A510P3FXZA Power Supply BN44--00222A

so time to backtrack PFC to find the problem, it is not uncommon to find cold solder joints on these boards so that a good place to start

[kevinm34232]

Re: PN50A510P3FXZA Power Supply BN44--00222A

Can you show me where to focus on, thank you.

[flocko]

Re: PN50A510P3FXZA Power Supply BN44--00222A

start from the 450v caps and work back to the two bridge rectifiers or the other way but also check the soldering and components( resistors/ diodes) as you go. Be safe use your meter set to continuity and no power the board till you find the problem would be my advice
I have taken a better look at the photo of the backside of your board and QS801 looks to be problem(burnt) and CB807 also does not look good (but as the STby is working could just be poor soldering)

[kevinm34232]

Re: PN50A510P3FXZA Power Supply BN44--00222A

QS801 is large transistor on top, what are you looking at exactly on the bottom please?

[flocko]

Re: PN50A510P3FXZA Power Supply BN44--00222A

what looks to be a big black burn mark on the center leg and the lack of solder on it.

[kevinm34232]

Re: PN50A510P3FXZA Power Supply BN44--00222A

Wow you're good.. QS801 was OK but found several cracked solder joints especially the one on the relay..

Everything is up and running again, thank you!

[flocko]

Re: PN50A510P3FXZA Power Supply BN44--00222A

Good find,always happy to help if I can

[ReeceyBurger123]

Re: PN50A510P3FXZA Power Supply BN44--00222A

Good work, be sure to fully resolder devices mounted on a heatsink too and any joints that look like they could go bad.