JVC Plasma GM-P420UG (won't come on)

[scalerwave]

It isn't my tv so I'm not sure what happened before it stopped working. As it is now, the status led will switch from green to yellow when the power button is pressed. I hear a relay click but that's about all.

I pulled it apart to check the power supply.... no obvious swollen caps. When I plug in the power cord, I hear the switch mode supply come up and then go down a few seconds later. I measure 5v on the supply line at first and then it goes to .9 or .6 and stays. On this model, the board on the left is called the X Main Board. I noticed that when I unplugged it from the PS, the 5v line would stay up so I figured I'd swap out that board but no help. I still have the same problem.

I haven't found a schematic for this set yet. I was just wondering if anyone here might be able to help out.

[martino]

Re: JVC Plasma GM-P420UG (won't come on)

Post some good clear pictures of the boards,that way the tech's here can help you a lot better

[scalerwave]

Re: JVC Plasma GM-P420UG (won't come on)

Ok, will do.

[jwilliams1967]

Re: JVC Plasma GM-P420UG (won't come on)

had a Samsung plasma that did that. check for poor solder connections on the transistors. can be diagnosed by pressing a isolated screwdriver on the heatsinks when plugged in . good luck

[Caleb]

Re: JVC Plasma GM-P420UG (won't come on)

Attaching Service Manual, no power board schematics but it does have trouble shooting flow charts.

[scalerwave]

Re: JVC Plasma GM-P420UG (won't come on)

Thanks for the info.

Here's a picture of the PS and X Main boards.

[scalerwave]

Re: JVC Plasma GM-P420UG (won't come on)

The owner decided that he didn't want the set anyway so I have adopted it.

I'm just gonna change out all the caps in the PS and see what happens... except for the 2 big ones.

I went ahead and bought one of those Blue ESR meters from Anatec too... for the next flat screen, I guess. I already have a Fluke with a cap checker but it doesn't do in-circuit checks. After reading more of this forum, I have a feeling I'll be seeing more leaky caps in the future.

After reading thru the JVC service manual, I found that the flow chart was just for the OSD service menu. There are some drawings but nothing really for the power supply.

Any help is appreciated though so thanks.

[freakaftr8]

Re: JVC Plasma GM-P420UG (won't come on)

Don't think that's a fix. Check solder connections to all mosfets first probe voltage off power supply in make sure that you don't have any shorted MOSFET's on the power supply is well

[tom66]

Re: JVC Plasma GM-P420UG (won't come on)

The PSU and sustains are full of high quality caps. It would be unlikely for them to be bad. Shot-gun replacing them will only cost you money.

[scalerwave]

Re: JVC Plasma GM-P420UG (won't come on)

Ok, I'll check.

The thing is... the PS stays up as long as the X main board (which has been replaced yesterday) is unplugged. If I had a shorted fet in the PS, wouldn't it stay down no matter what?

[tom66]

Re: JVC Plasma GM-P420UG (won't come on)

Yes but what if the short was on the X-main?

[scalerwave]

Re: JVC Plasma GM-P420UG (won't come on)

Yes but what if the short was on the X-main?

That's what I was hoping when I swapped out the X Main board with a known good one... but no luck... same problem. The PS shuts down...but stays up as long as the X Main is not connected to the PS.

The X Main board does connect to the Relay Recover Board and Signal Relay Boards. I suppose I could disconnect them from the X Main and see what happens.

My theory today was maybe the X Main board is just too much for the PS due to leaky caps however now that I remember, I tried disconnecting the Y Main board but leaving the X Main connected and the PS went down then too.

[scalerwave]

Re: JVC Plasma GM-P420UG (won't come on)

That's what I was hoping when I swapped out the X Main board with a known good one... but no luck... same problem. The PS shuts down...but stays up as long as the X Main is not connected to the PS.

The X Main board does connect to the Relay Recover Board and Signal Relay Boards. I suppose I could disconnect them from the X Main and see what happens.

My theory today was maybe the X Main board is just too much for the PS due to leaky caps however now that I remember, I tried disconnecting the Y Main board but leaving the X Main connected and the PS went down then too.

I found some better pictures of the boards....

[steveg_nh]

Re: JVC Plasma GM-P420UG (won't come on)

Did you ever get this set working? I have a similar issue. No picture, but audio. I can briefly see the picture as move through the available input resolutions on component, but then it goes to "No Sync". I'm thinking a bad X or Z sustain board.

Thanks