LG 50PM670S no image

[tietoharrastelija]

Hi,
I've got from my friend LG 50PM670S Plasma-TV which doesn't start. (Standby light on, when press power it goes for sec of..)

Replaced shorted Q404: 30F126, Q509: KF7N60F:, Q403: 30F126, D402: SF20A300H and few small caps
from Y-sus board (EAX64282201). Some screwhole shorted to ground (fixed it tape)

Now I hear a faint buzzing, logic board green led is on and center board where flex multiple flex cable goes it green led blinking sequence. Also chips going to warm to touch.

Checked VA+VS+5V+17V voltages there are OK, also resoldered coils and transformers.. (checked Y buffer board cap voltage, it was ~5v)

What to do now??

[Hamie]

Re: LG 50PM670S no image

What's the -vy vsc and zbias voltages? If all ok and matching the panel sticker running test patterns on the logic board would be the next step.

[tietoharrastelija]

Re: LG 50PM670S no image

What's the -vy vsc and zbias voltages? If all ok and matching the panel sticker running test patterns on the logic board would be the next step.

VY = 204v
VSC = 204-205v
VZB = 150V (ok)

Panel sticker: Voltage setting: 5.0V/VA:55V/VS:205V

How to run test patterns?

[tvtimmy]

Re: LG 50PM670S no image

Put a piece of wire in the 2 holes and disconnect the ribbon.

[Hamie]

Re: LG 50PM670S no image

Vy and vsc dont look right.
Upload a photo of your panel sticker just to confirm.

[tietoharrastelija]

Re: LG 50PM670S no image

Vy and vsc dont look right.
Upload a photo of your panel sticker just to confirm.

See attachment.

[tietoharrastelija]

Re: LG 50PM670S no image

Put a piece of wire in the 2 holes and disconnect the ribbon.

Tested, but not doing anything.

D101 green led still blinking like something code (one long, and few short)

EDIT: Sound working OK via HDMi

[tietoharrastelija]

Re: LG 50PM670S no image

ZSUB board voltage capacitor etc is 15v IS that correct?

[tietoharrastelija]

Re: LG 50PM670S no image

Found another problem from Y Sus board.

Can place screws only 1 and 2 screwholes and tighten. When trying place screw or tighten screwhole 3-7 tv not start (only standby led off for few seconds).

Screwholes 6 and 7 have small crack around hole. Tried place screw to hole 4 and got sparks. (holes shorting (?)) they are ground points to chassis??

(See photos)

[mmartell]

Re: LG 50PM670S no image

-Vy should be -190v according to sticker. You are reporting 204v (-204v is using the proper test points?)

Maybe you're sending that circuit into shutdown ? Trim down -Vy voltage.

Re the 15v on the Zsus I don't know which cap you're referring to but there is usually a 12-15v supply on the Zsus. Comes from the Ysus and is usually routed through the logic board.

If the ground points around the screw holes are oxidized from previous arcing then rub them clean with emory cloth or similar so they make good contact. Otherwise you have more serious issues.

[tietoharrastelija]

Re: LG 50PM670S no image

-Vy should be -190v according to sticker. You are reporting 204v (-204v is using the proper test points?)

Maybe you're sending that circuit into shutdown ? Trim down -Vy voltage.

Re the 15v on the Zsus I don't know which cap you're referring to but there is usually a 12-15v supply on the Zsus. Comes from the Ysus and is usually routed through the logic board.

If the ground points around the screw holes are oxidized from previous arcing then rub them clean with emory cloth or similar so they make good contact. Otherwise you have more serious issues.

Okay, maybe wrong test point for -vy. Found another shorted from diode (replaced it), and checked 4 components for shorts removing them (but false short). TV goes to protect mode (aka goes to standby one second when press Power Button). When I place tape under screwhole (3-7) go voltages and TV powers on. But without tape and screws it sparkling. Mysterious problem..

[Hamie]

Re: LG 50PM670S no image

The vy and vsc test points are the 2 resistors close to the join for the buffers put your probes to the corresponding - and + marks. You should never run a y sus without ALL the screws in place or you could potentially damage the repair work you have already done.

[tietoharrastelija]

Re: LG 50PM670S no image

The vy and vsc test points are the 2 resistors close to the join for the buffers put your probes to the corresponding - and + marks. You should never run a y sus without ALL the screws in place or you could potentially damage the repair work you have already done.

Can't meter now vy voltage (also turned trim vy) it always on for one second and after it back to standby.. Placed all screws etc.. something shorting (?) but checked..

EDIT: Tested +VS pin (from connector) and groud chassis DMM Said 413 ohm, is that OK?

[Hamie]

Re: LG 50PM670S no image

No if VS to ground is only 430ohm then you have a fault sure it wasn't 430k?
If not then you're on the right track.

[dick_barton]

Re: LG 50PM670S no image

Are you sure Hamie? (205V/430 ohms) = 0.48Amp The sticker on the panel rates the 205V supply @ 1.4Amp

[tietoharrastelija]

Re: LG 50PM670S no image

No if VS to ground is only 430ohm then you have a fault sure it wasn't 430k?
If not then you're on the right track.

Tested it few moments ago on table. +VS and center screwholes resistance 413 ohm (DMM 2000 ohm range).

[tietoharrastelija]

Re: LG 50PM670S no image

Looks like Q404 ja Q403 (30F126) again shorted ( 4 ohm and other 14 ohm), replaced again and +VS ja GND now no conductive (infinite resistance)

[dick_barton]

Re: LG 50PM670S no image

There was a discussion a while ago about the number of fake Mosfets on sale on eBay so I would only buy replacements from a reputable supplier.

[tietoharrastelija]

Re: LG 50PM670S no image

There was a discussion a while ago about the number of fake Mosfets on sale on eBay so I would only buy replacements from a reputable supplier.

Can't find 30F126 from any a reputable supplier. Purchased components from UTSource. 30F126 looks like used (thermalpaste residue on component)...

[tietoharrastelija]

Re: LG 50PM670S no image

Tested Y Buffers without TV -> no shorted. I put everything back (also screws) and tested. No magic smoke, TV started internally logic board green led and center board led blinking. Also standby goes to on. But still no picture. Yesterday I was turned trimming potentiometer (Maybe VY voltage), changed it yesterday same position but maybe not same position (Can that cause no picture??) How to set it correct position?