LG 42PQ3000 - red then blue blinks no picture

[tom66]

No Vs/Va, red light then blue light with no picture (sound might work)
Found PSU to have blown FETs Q801,Q802 (shorted)
Will also replace: R801,R802,R803,R804,D801,D802,D805,F801,IC801

Power board parts:
Q801: Sub with IRFB11N50APBF
Q802: Sub with IRFB11N50APBF
R801: 51R THT 1/4W
R802: 20k SMD 0805
R803: 51R THT 1/4W
R804: 20k SMD 0805
D801: SB140A -> 1N5822
D802: SB140A -> 1N5822
D805: MUR160
IC801: L6599D
F801: 4AH 250V

The YSUS VS fuse was found blown, however, no parts could be found shorted; no short either end of fuse and no IGBTs/FETs short.

Possibly repeated turning on/off after YSUS failure trying to get set to work made FETs fail on PSU? It is very odd that both failed...

First new LG plasma

[tom66]

Re: LG 42PQ3000 - red then blue blinks no picture

TV is now fixed. The fuse on the Y-sus, and power board fault were the only issues.

Picture quality is mediocre. Black level is pretty poor, but overall picture contrast is good.

[vinceroger69]

Re: LG 42PQ3000 - red then blue blinks no picture

do these suffer the same problem as in you need to update the firmware to get rid of the dots etc on the picture or is that just when you swop boards rather than repair them?

[tom66]

Re: LG 42PQ3000 - red then blue blinks no picture

This has some very minor maldischarge, but otherwise no problems. Very watchable image.

[vinceroger69]

Re: LG 42PQ3000 - red then blue blinks no picture

what does cause the maldischarge any idea? but does not look a bad set at all imo another one saved.

[tom66]

Re: LG 42PQ3000 - red then blue blinks no picture

Ion implantation in the panel, each sustain cycle basically wears out the pixels and they get easier or harder to discharge. This means maldischarge can occur as the panel ages.

A well designed control firmware (which is what runs on the control board) will adjust the drive waveforms to the panel as it ages, preventing maldischarge from occurring.

[vinceroger69]

Re: LG 42PQ3000 - red then blue blinks no picture

cool a easy explanation i can understand is it only lg that suffer this never saw it mentioned on panasonic sets.

[tom66]

Re: LG 42PQ3000 - red then blue blinks no picture

Panasonic did the firmware right - as the panel ages the waveforms change slightly, preventing maldischarge.

[vinceroger69]

Re: LG 42PQ3000 - red then blue blinks no picture

cool thats good to here i hope to have my panasonic for a while.

[tom66]

Re: LG 42PQ3000 - red then blue blinks no picture

Yep as I said one with over 13,500 hours still picture perfect and no burn in.
This has burn in from the Cbeebies logo, I'm guessing the people I bought it off had kids...

[vinceroger69]

Re: LG 42PQ3000 - red then blue blinks no picture

does burn in ever go away or does it just fade away to a watchable picture ?

[tom66]

Re: LG 42PQ3000 - red then blue blinks no picture

It is permanent. Image retention (IR) can fade. IR is usually visible on dark image only.
Burn in is common to all types of emissive displays, pixels that are used more will wear out quicker.

LCDs do not burn in because the pixels do not wear out directly, except for certain cheaper displays where the pixels are driven so poorly they get a DC-bias (VCOM fault.)

[Alastair E]

Re: LG 42PQ3000 - red then blue blinks no picture

does burn in ever go away or does it just fade away to a watchable picture ?

I had a Philips set that had the 'Muted sound' logo in top left-hand corner burned in the screen....

Was very noticable initially, but after a week or so had faded to the point you had to go looking for it to see it....

Gawd knows just why the original owner had the sound muted for such a considerable time though!

I firmly believe the panels do have a memory of sorts,--a static build-up deep into the cells or summit-- even remembering the mal-discharge condition to some extent--

That LG that I have with 17,000 hours on, had it--even after firmware update --just very slight and more when it was stone-cold after the update.

A week running with the new firmware, and now there's none at all--even when the panel first initialises with that faint glow from stone-cold, where previously for that second or so--it was snow-storm time!
--Nothing has changed, nothing has been adjusted--its got better on its own leading me to think the above....

[Fwrothy]

Re: LG 42PQ3000 - red then blue blinks no picture

Nice work Tom! MOSFETs seem to be such a common failure item. It looks like you upgraded two diodes. Did you also 'beef' up the MOSFETs or just substitute based on convienence?

[tom66]

Re: LG 42PQ3000 - red then blue blinks no picture

Nice work Tom! MOSFETs seem to be such a common failure item. It looks like you upgraded two diodes. Did you also 'beef' up the MOSFETs or just substitute based on convienence?

The MOSFETs were like for like replacements. I reckon the failure occurred due to the Y-sus fuse popping and the user cycling the TV far too many times to get it to turn on. The power up process is the most stressful time for a power supply as with discharged output capacitance, the power supply is essentially driving a shorted load for about 1 second. Note these LGs discharge Vs/Va at switch off so they do not benefit from the Vs remaining high for some time.

The diodes were uprated for convenience, in that section the average current is <50mA or so.

[tom66]

Re: LG 42PQ3000 - red then blue blinks no picture

I firmly believe the panels do have a memory of sorts,--a static build-up deep into the cells or summit-- even remembering the mal-discharge condition to some extent

They do have memory! It's called wall charge and is fundamental to the operation of a plasma display. The IRF document is useful but this is better:


Panasonic explain the first PDP they made (2001 PDP.) However, technology has not changed much since then. (The process has simply been refined and simplified.)

[tom66]

Re: LG 42PQ3000 - red then blue blinks no picture

Out of interest, anyone know how to get into the service menu for this thing? MENU on TV and MENU on remote for 10 seconds does not work. The service manual indicates a factory remote as being necessary, but I'd like to avoid that.