LG 50PV400 No Picture

[neilc6]

When I picked this up, the previous owner claimed it was LED but I was a bit skeptical because of the greenish tint of the pic of the screen. Anyway, it's my problem now. Also said there was sound but no picture. This is my first plasma so please be gentle with me. Plasmas aren't worth that much so don't want to replace the PS board.

Looks like problem is with the power supply. There are no voltages coming out of it except standby voltage. Looked at previous threads on a similar LG model, there is a common failure with a square 22nF polypropylene cap but this power supply has a different one.

Powering up, relay clicks and front LED lights up.

Power supply is EAY62171103. No bulged electrolytic capacitors, all fuses are ok, 120VAC measured at AC input on board.

VS/VA/M5V to YSUS board all measure 0V

M_ON/Auto_gnd 0V
Rl_on/AC_DET 0V
Stdby 5.3V
5.1V 0.2
5.1V 0.2V
GND 0V
17V 0V

[neilc6]

Re: LG 50PV400 No Picture

Actually, the relay clicks twice and the power supply seems to be shutting down since there is 17V when I plug it in. Found a training manual here and guess I need to go through it.

[Hamie]

Re: LG 50PV400 No Picture

Disconnect y and z sus.

On power supply jump standby to RL-On

Vs and va voltages should now come up.

[neilc6]

Re: LG 50PV400 No Picture

On closer inspection, I was measuring the voltages on the outer pins of the 18 pin connector. The TV attempts to startup twice, with relays clicking on and off each time. When on for a few seconds, I get the following voltages
M_ON 3.3V
RL_ON 2.45V
STDBY 5.25V
5.1V 5.23V
17V 16.8V
AC_DET 4.4V
ERRDET 4.99V

Disconnect y and z sus.
On power supply jump standby to RL-On
Vs and va voltages should now come up.

With RL_ON jumped to standby and YSUS disconnected, I measure Vs=205V, Va=53V, M5V=5.3V

Does this mean the problem is with the YSUS board?? I also cut the autognd line but it behaved the same so I soldered it back.

[Hamie]

Re: LG 50PV400 No Picture

You can leave the power supply jumper in place.

Now plug back in the y-sustain and check for vsc and -vy voltages.

Also check VZB (Zbias) on the z-sustain.

[Hamie]

Re: LG 50PV400 No Picture

Also you said you cut the autogen jumper... Did you try test patterns with the power supply jumped on?

If not, put it back.

[neilc6]

Re: LG 50PV400 No Picture

With the YSUS power cable disconnected, I checked the resistance of Vs, Va and M5V. Vs indicated a short so I unplugged the cable going from YSUS to ZSUS next. Vs resistance was ok on YSUS so I inspected the ZSUS board and found scorch marks on a row of FETs and diodes under one heatsink.

Edit: Continuity testing showed every part under that heatsink is shorted. D114, D118 - RD2003 and Q109, Q106, Q107, Q110 - FGPF4633. Same parts under the second heatsink test good.

Edit2: Could only find the transistors at Mouser and they were $1.80 each. Ordered a replacement ZSUS board on ebay for $17 instead.

[neilc6]

Re: LG 50PV400 No Picture

Got the new (used) zsus board in. TV starts up but the picture isn't sharp and the colors are off (see attachments).

Vzb=130.7V
Va=55.2V
Vs=205V
M5V=5.12V

Suggestions?

[Decl]

Re: LG 50PV400 No Picture

http://manualsbrain.com/en/manuals/1504519/

[Hamie]

Re: LG 50PV400 No Picture

So what's the vy and vsc voltages?

[neilc6]

Re: LG 50PV400 No Picture

Vsc=150.0
Vy=189.0

There is a slight hum in the area of the YSUS board

This post indicates this model (same as 50PV450) has a common problem with cold solder joints on the two large coils on both ZSUS and YSUS boards. I have reheated and put fresh solder on these coils with no improvement. https://www.badcaps.net/forum/showthread.php?t=43729

This post indicates I might still have a bad Zsus board. There is blotchiness and ghosting along with the colors being off. https://www.badcaps.net/forum/showthread.php?t=18542

[neilc6]

Re: LG 50PV400 No Picture

Any opinions on whether or not I should try another zsus board?

The replacement I got was physically dirty and looked like it was pulled from a tv found in a trash pile outside. The seller did refund me for it already.

[vasia]

Re: LG 50PV400 No Picture

http://manualsbrain.com/en/manuals/1504519/

Thanks