LG 60PB6600-UA No picture, whine from PSU

[DXseekerMO]

Re: LG 60PB6600-UA No picture, whine from PSU

Look very closely at cap C975 on the top of the lower buffer board. It looks fractured to me, diagonally from the brown spot.

On the Y-sus board perform a continuity check on resistor R559, circled in light blue, in both directions. Does it test open in one direction and very high resistance in the other?

Check the transistors Q507, Q552 and Q553 under the heat sink, outlined in red, in diode check mode. Do you get any abnormal low readings, like .170 or close?

Picture courtesy of ShopJimmy.com

Let us know.

[KuroYamaneko]

Re: LG 60PB6600-UA No picture, whine from PSU

I've just checked them.

Resistor has no connectivity either way.

I'm not sure if I've checked the transistors correctly, but they read as follows;
Q507 positive left, negitive right - 1.5
Positive left, negative centre - 1.734
Negative centre, positive right - 0.508

Q552 same order as above. 0.886
1.114
0.397

Q553 0.084
0.095
0.012

Thanks

[DXseekerMO]

Re: LG 60PB6600-UA No picture, whine from PSU

This is a common failure for this set. Although the mode of failure is not fully understood it appears either C873 and/or C975 shorts and takes out Q552/553 which causes fusible resistor R559 to go open, or Q552/553 shorts out, causes R559 to go open and takes out C873 and/or C975.

It is necessary to replace Q507/552/553 with this failure along with R559 and check diodes D556 and 557 on the Y-sus. I would also replace both C873 and C975 on both buffer boards since both are probably stressed during this failure.

This thread should give you more information: https://www.badcaps.net/forum/showth...light=60pb6650

When I replace SMD caps like those I use two soldering irons, one on each side of the cap, make sure the solder is melted then pluck the cap off the board using both soldering irons like a pincer.

My TV had the same symptoms as yours, but the only question that remains in my mind is the whiny power supply. I'd check the PSU for cold/cracked solder joints especially on the transistors and transformers first, just to make sure the PSU is tip-top before you power it up after the fix is applied.

Let us know if you have more questions

[KuroYamaneko]

Re: LG 60PB6600-UA No picture, whine from PSU

Thank you very much for the help, I really appreciate it.

I will look into getting those replaced.
having a hard time finding 2sk3773 transistors. and is the C975 the same capacitance as C873? If so, I am only finding either 3.9nf or 4.7nf capacitors.

Cheers!

[DXseekerMO]

Re: LG 60PB6600-UA No picture, whine from PSU

C975 and C873 are both the same.

I will try to find my order from Digikey and see if I can get you the numbers of the parts I bought

[KuroYamaneko]

Re: LG 60PB6600-UA No picture, whine from PSU

Many thanks!

[DXseekerMO]

Re: LG 60PB6600-UA No picture, whine from PSU

From DigiKey:
FQPF16N25C-ND MOSFET N-CH 250V 15.6A TO-220 replacement for Q552/553

KNP100JR-73-2R RES 2 OHM 1W 5% AXIAL replacement for R559 SEE NOTE BELOW!!!

399-15095-1-ND C1206C222KBRAC7800 CAP CER 2200PF 630V X7R 1206 replacement for C873/975

CW7270-ND CW7270 HEAT SINK GREASE SILICONE FREE (for installation of transistors)

From EBAY seller ser41sosa

TK8A60DA K8A60DA ORIGINAL FAIRCHILD MOSFET replacement for Q507

You can find part numbers for equivalent transistors HERE: https://alltransistors.com/mosfet/crsearch.php Input your transistor number in the search box

NOTE: This resistor should be 10% tolerance, not 5%