JVC plasma picture fault

[reddiesel]

Hi im hoping someone can help me sort a fault on a JVC PD-42DX6BJ plasma the picture has gone dark with what looks like a sparkly affect in certain patches, looking closer it looks like the pixels are normal in the patches, the picture can still be seen it just looks washed out like looking through a fog, it started a few months ago and cleared after half hour or so, then it seemed to have cured itself and has been fine, now its back and permanent, ive had various advice saying the X sus or Y sus boards or someone said buffers which i take it is either of two on the bottom or the Y sus upper and lower ones ?
i'd be greatfull if it could be narrowed down a bit.
I've got the back off now and cant see any bulging caps

[PlainBill]

Re: JVC plasma picture fault

Hi im hoping someone can help me sort a fault on a JVC PD-42DX6BJ plasma the picture has gone dark with what looks like a sparkly affect in certain patches, looking closer it looks like the pixels are normal in the patches, the picture can still be seen it just looks washed out like looking through a fog, it started a few months ago and cleared after half hour or so, then it seemed to have cured itself and has been fine, now its back and permanent, ive had various advice saying the X sus or Y sus boards or someone said buffers which i take it is either of two on the bottom or the Y sus upper and lower ones ?
i'd be greatfull if it could be narrowed down a bit.
I've got the back off now and cant see any bulging caps

That sounds like a bad Z-sustain.

Pictures help us help you. In this case, one of the back of the TV to start, and a second of the Z-Sustain - right side as viewed from the back.

For best results, pictures should be well lit and in focus, at least 1000 x 1000 pixels, but not over 200 pixels due to site limitations. Attach them using 'Manage Attachments' - below the text entry area.

PlainBill

[reddiesel]

Re: JVC plasma picture fault

Thanks PlainBill .

[PlainBill]

Re: JVC plasma picture fault

Thanks PlainBill .

Awww, crud!!! I thought you had a set with the LG Electronics bad hybrid problem. Instead, you have a set with the Samsung 42" HD V4 panel. The LG was best solved by replacing the Z-Sustain.

I'm well out of my comfort zone on this. This panel is notorious for blowing the Y-main (AKA Y-Sustain) and Y-Buffers in a cascading failure. The cost of replacing all three is in the order of $200, which is makes the repair uneconomical. On the other hand, if my diagnosis is correct, the X-Main is available for $25 and up on eBay.

Philips used the same panel in a few of their TVs. The service manual has suggestions on troubleshooting this problem. It's available here.

[reddiesel]

Re: JVC plasma picture fault

Thanks for your help iv'e ordered a board off ebay worth a try, only £11 (im in the uk), i'l let you know how i get on.

[reddiesel]

Re: JVC plasma picture fault

Board came today, fitted it and still the same, i tried to get a decent pic but they dont show up well, this is one of a blue screen.
I will have to try and get hold of a Y sus and buffers i guess ?
Will i have to adjust the main board when i fit that ? i have the service manual.

[PlainBill]

Re: JVC plasma picture fault

Board came today, fitted it and still the same, i tried to get a decent pic but they dont show up well, this is one of a blue screen.
I will have to try and get hold of a Y sus and buffers i guess ?
Will i have to adjust the main board when i fit that ? i have the service manual.

Before spending any more money, check the voltages out of the power supply, in particular those voltages going to the Y and X main boards. This is NOT the typical Y main / Y buffer failure.

PlainBill

[reddiesel]

Re: JVC plasma picture fault

Ok the voltages on the X main read pin 1 vdd 5v, 2 vcc 15.1v, 5 ve 90.1v, 10 and 11 vs 200.6v, the voltage chart says ve 99.6 and vs 208.6v on cn8002 which is that connector.
The Y sus reads vdd 5v, vcc 15v, v scan 190v, v set 195.1, vs 201.
chart says v set 194, vs 208.5.
so slightly low volts, i let the set warm up before i took readings, is that any help ?

[PlainBill]

Re: JVC plasma picture fault

Ok the voltages on the X main read pin 1 vdd 5v, 2 vcc 15.1v, 5 ve 90.1v, 10 and 11 vs 200.6v, the voltage chart says ve 99.6 and vs 208.6v on cn8002 which is that connector.
The Y sus reads vdd 5v, vcc 15v, v scan 190v, v set 195.1, vs 201.
chart says v set 194, vs 208.5.
so slightly low volts, i let the set warm up before i took readings, is that any help ?

I'll repeat - I'm way out of my comfort zone on this. Those voltages are more than slightly low. What kind of a DMM do you have? I'm reluctant to suggest tweaking the power supply; plasma panels are supposed to be intolerant of over voltage.

If you have a $3.00 Chinese meter from eBay, I don't have much confidence. If on the other hand you have a Fluke, I'd say go for it - except that raises the question of 'why did the voltages drop?'

PlainBill

[tom66]

Re: JVC plasma picture fault

The tolerances on these voltages are usually +/-2%.

A cheapo meter might be +/-2%, worst case. In fact most Mastech cheapies I've used are at least +/-0.5% and they do meet this specification. Surprising for the price, really...

All the measurements have drifted by 3% or more, and each a varying amount, so I would rule out the multimeter.

From what little I know about PDPs, I would say the -Vsc (Vscan) voltage is causing the problem. That can cause bad colour and brightness. Maybe set it to 0.5 - 1V below its nominal voltage just to be sure, should be much better.

PlainBill: These voltage adjustments all use potentiometers, usually trim pots. The problem with these small trim pots is they are sensitive to vibration and heat. They can drift over time due to the high temperature inside most of these displays. Also, if the set is moved, or bumped, they can drift too.

[PlainBill]

Re: JVC plasma picture fault

The tolerances on these voltages are usually +/-2%.

A cheapo meter might be +/-2%, worst case. In fact most Mastech cheapies I've used are at least +/-0.5% and they do meet this specification. Surprising for the price, really...

All the measurements have drifted by 3% or more, and each a varying amount, so I would rule out the multimeter.

From what little I know about PDPs, I would say the -Vsc (Vscan) voltage is causing the problem. That can cause bad colour and brightness. Maybe set it to 0.5 - 1V below its nominal voltage just to be sure, should be much better.

PlainBill: These voltage adjustments all use potentiometers, usually trim pots. The problem with these small trim pots is they are sensitive to vibration and heat. They can drift over time due to the high temperature inside most of these displays. Also, if the set is moved, or bumped, they can drift too.

DUH!!! I knew about the pots; somehow the memories of squirting in contact cleaner and spinning the shaft back and forth to 'cure' a noisy volume control have faded.

PlainBill

[reddiesel]

Re: JVC plasma picture fault

It's a UNI-T meter i think i paid about £40 for it. Tom was right about the pots as soon as i touched the vs one it went shooting up,dead sensitive, i adjusted the vs and the ve to just under the stated voltage, the vscan i didnt touch as it was bang on, i made sure the adjustments were stable.
Stood the panel up and tried it and to my surprise a beautiful bright clear picture, its been left on a couple of hours now and seems fine.
Thanks very much PlainBill and tom66 i wouldnt have done it without your help !

[tom66]

Re: JVC plasma picture fault

It's a UNI-T meter i think i paid about £40 for it. Tom was right about the pots as soon as i touched the vs one it went shooting up,dead sensitive, i adjusted the vs and the ve to just under the stated voltage, the vscan i didnt touch as it was bang on, i made sure the adjustments were stable.
Stood the panel up and tried it and to my surprise a beautiful bright clear picture, its been left on a couple of hours now and seems fine.
Thanks very much PlainBill and tom66 i wouldnt have done it without your help !

You may want to use some Loctite or general purpose glue on the pots. Just enough to hold them in place, but not too much so you can't adjust them later (make it so that a turn with the screwdriver will break the glue.) This will stop them drifting in future so the picture should last longer.

Glad to hear your TV is now working!

Uni-T meters are pretty good for the price, so I don't think it would be giving erroneous values.

[reddiesel]

Re: JVC plasma picture fault

The blacks are a lot better than before so it must have been faulty for a while, i bought it spares or repair a couple of years ago thinking at worse i would have to replace the boards, it would switch off after 2 minutes and no volume, it turned out that the previous owners youngster had been poking a biro or something in the headphone socket and opened the contacts out, and pushed the rubber part of the standbye button inside so it was holding it on, so a dead easy fix, im still smlling lol.

[reddiesel]

Re: JVC plasma picture fault

You may want to use some Loctite or general purpose glue on the pots. Just enough to hold them in place, but not too much so you can't adjust them later (make it so that a turn with the screwdriver will break the glue.) This will stop them drifting in future so the picture should last longer.

Glad to hear your TV is now working!

Uni-T meters are pretty good for the price, so I don't think it would be giving erroneous values.

Thats a good idea i'l do that !

[tom66]

Re: JVC plasma picture fault

The blacks are a lot better than before so it must have been faulty for a while, i bought it spares or repair a couple of years ago thinking at worse i would have to replace the boards, it would switch off after 2 minutes and no volume, it turned out that the previous owners youngster had been poking a biro or something in the headphone socket and opened the contacts out, and pushed the rubber part of the standbye button inside so it was holding it on, so a dead easy fix, im still smlling lol.

Yeah I've had a dead easy fix before the guy had obviously taken apart his TV in an attempt to fix it and messed something up; I just reseated all the connectors on the power supply and it worked straight away... now sold with no complaints.

[reddiesel]

Re: JVC plasma picture fault

Well it worked fine for a couple of months, then one day switched on and it had Horizontal stripes mostly on the bottom half and a few on the top so i got a used replacement y sus tried it and it was exactly the same, so i thought it must be the buffers, managed to get a complete scrap tv off ebay cheaply, swapped the buffers and just a black screen with a few sparkles, so i thought just my luck same fault, i tried the old buffers back in and it was now still a black screen so i thought i must have blown the y sus but i still have the spare one.
The buffers seem to be the most expensive type on ebay on this panel about £50 each new so i got another used pair from a broken screen off you guessed it ebay, i swapped the y sus and put in the buffers and its still a black screen with a few sparkles ? i know im taking a chance with used parts but now im not sure what to do, is it worth trying another y sus ? the voltages are ok .

Merry Christmas by the way.

[tom66]

Re: JVC plasma picture fault

Horizontal stripes mostly on the bottom half would be a bad bottom buffer.

Did you try a complete board swap (every board)? Maybe the best approach since you've got a cheap TV with probably good parts.