Samsung Plasma PN43D450A2D No Power

[CDNBrewer]

Hello, I have a Samsung Plasma TV - Model # PN43D450A2D

This was my parents TV and the initial symptoms were that the display was hard to turn on with the display making various clicking noises until one day it would not turn on anymore.

I took a look and found a couple 1000uF capacitors (i believe on the low voltage size) that had leaked out their electrolyte and did not test well on a tester. I replaced them but still no dice.

When the TV is plugged in, there is no clicking, LED status lights (on PCB boards or the front display) and the power on button does not work.

On connector CN801 I am reading 3.3v on PS-ON but 0v on STBY. This remains the same regardless if the other connectors are plugged into the main power board or not.

My initial guess is that the problem lies within the power supply. I've reflowed all the joints for components with heatsinks and this has not helped.

Any suggestions or steps i can take to troubleshoot this would be appreciated. Thank you!

[CDNBrewer]

One more detail - the Power supply Part number is BN44-00442A however it appears it may also be model number BN44-00443A, BN44-00444A or BN44-00444D for various size of TVs and it appears they populate different components. In other words if someone has a schematic for any of these models it would be a big help.

[nomoresonys]

Could be some more of those electrolytic caps have gone bad, hard to tell without a tester. But they have been working hard for quite a while. Can do a dirty test that if they don't at least pass then you can be pretty sure it's bad. Will post it shortly.

[nomoresonys]

Any tv in this age range I always suspect capacitors first, electrolytics are usually the first caps to go bad. You can do what's called a dirty test, it isn't a full test but if it isn't at least passing the dirty test then you know it's probably a bad cap, demonstration there, notice he puts his meter on 20K ohms setting, at least test all of the electrolytics, no need to de-solder, test them in circuit: https://www.youtube.com/watch?v=NqvL7Cyemiw

[CDNBrewer]

thanks for the quick reply! I did a "dirty" test of all the electrolytic caps on the board and they all seem to be fine, except for a couple, which i needed to take out of circuit for which i then tested on my LCR meter and they are within spec. Any other suggestions?

[nomoresonys]

Another quick test I do is use a hairdryer to heat up the electrolytic caps for a couple minutes then try it while it's still hot. This allows a bad/marginal cap to have lower esr enough to work for a brief time, doesn't work if the cap is too far gone but just another easy thing to do.

[nomoresonys]

Here's some fault finding from a clever farm dad: https://www.youtube.com/watch?v=KYKw9QTJhvM

[nomoresonys]

One thing about plasmas, when testing and removing and putting back boards. Make sure you put ALL screws back in and snug them up so nothing shorts out.

[nomoresonys]

Seems like what goes bad a lot of times is the transistors on the Y-board when Y-board is the problem, easy enough to test with the board out.

[CDNBrewer]

Made some more progress tonight. I can confirm that my power supply board is not turning on the 5V Standby Signal. I don't have exact schematics (which is tough to trace this all out) but from what I deduce is this:

The 3BR2565JF power supply regulator is initially working and generating the 15v and 5v respectively on the cold side of the board.
The initial 5V signal (STBY-HEAD) feeds a MCV14A microcontroller
This microcontroller is getting 5V across the supply and ground
It appears this microcontroller has output pins to turn on the regular standby, relay, 15v and another 5.3v signal and a "main" on. It also appears that it has a variety of divider resistors that can be used to detect if these signals are working (such as standby, VS, VA, D5.3V, D15V, PFC_OK, VS_ON, PS_ON).

I suppose the microcontroller has some sort of start up sequence where it turns on separate rails one at a time and ultimately waits for the PS_ON signal from the brainbox to turn the whole thing on.

At this point I am somewhat stuck and don't know how to take it further from here. Does anyone know roughly what the start-up sequence might be for these microcontrollers?

Thanks!