NEC PX-42vp4g Plasma panel goes into standby

Rodoz6 · Joined: 08 Mar 2009 Posts: 2

My plasma panel goes into standby when I turn it on Its boots up runs for 5 seconds and then shuts down to standby. Checked the supplies. The HV 170v supply begins to drop after turn on the cuts off back to standby when it drops tp about 136V. Picture does appear ok before switches itself off. Replaced a couple of caps with low readings and poor ESR but all the others look fine. No schematic for me to work with. Can any body help with this problem? It is evidently a common one for this series but none of the databases seem to have a fix posted. Unusual for such a known problem. This one has me baffled.

I hope someone can advise me how they fixed theirs

Regards Rod

minnie · Joined: 18 Aug 2005 Posts: 2880 Location: Hell

Unplug the x & y sustain boards and see it the set stays on.

Rodoz6 · Joined: 08 Mar 2009 Posts: 2

Further information on the power supply in the Further information on the power supply in the NEC PX-42vp4g plasma. The supply is not NEC

but Origin Electric Co China supply model PNT-426, pcb PKG-

1953. I believe it may be used in other plasmas too. I

replaced any caps that had poor ESR readings. Supply ran but

the 170v rail would slowly drop from to about 136v then supply

would go into standby. Picture was fine until about 145v then

a bit noisy. Eventually with me turning it on and off to

diagnose rails the supply failed. Now I can see B+ HV DC pre

regulator. Also 5v out of 74L05 for standby but turned off by

protection before leaving the board to standby switch.

Choppers not running. . The supply is not NEC

but Origin Electric Co China supply model PNT-426, pcb PKG-

1953. I believe it may be used in other plasmas too. I

replaced any caps that had poor ESR readings. Supply ran but

the 170v rail would slowly drop from to about 136v then supply

would go into standby. Picture was fine until about 145v then

a bit noisy. Eventually with me turning it on and off to

diagnose rails the supply failed. Now I can see B+ HV DC pre

regulator. Also 5v out of 74L05 for standby but turned off by

protection before leaving the board to standby switch.

Choppers not running. Cheers from Rod

jts1957 · Joined: 24 Nov 2008 Posts: 2476 Location: Far, Far Away

Any one else hear an echo in here? Laughing

envisionelec · Guest

I found a complete lack of information on this set...so I plan to change that. I have a big pile of these sets from a local club and they've asked me to repair them. It's my first plasma repair, but I design SMPS power supplies, so this is no problem whatsoever. The SMPS has been "repaired" once before, presumably unsuccessfully.

I'll report what I find.

envisionelec · Guest

The NEC PX-42VP4g is similar, if not exactly the same as the Pioneer PDP-424MX. There is a service document online at Scribd (I can't post a link to the site...sorry!)

I'll get more data as I work on the supply and read this manual. I did note that the Pioneer has two fans installed that are missing in the NEC. However, the NEC has mounting locations for the fans. Since my application is commercial, I will plan to install the fans as well.

envisionelec · Guest

With respect to the 170V not maintaining regulation, check the 5 chained resistors coming off the VS adjustment potentiometer. Also, the two MosFets nearby (right behind the large 1500uF 200V cap) are driven by a regulator chip through a set of resistors paralleled with diodes. These resistors may need resoldered. Check the 1500uF capacitor for any signs of bulging. It's probably a good idea to replace this, anyway, because it's operating so closely to its maximum voltage.

waxhead · Joined: 24 Sep 2009 Posts: 1

does the standby light flash red/green red/green?

also if you need a psu board let me know because i have two of them

zvisegal · Joined: 28 Sep 2009 Posts: 1

If the red/green LED blinks - you can reset it by pressining the EXIT buttom while turning POWER ON.

I have similar problem.

Originally I got spots al over the screen. Than I replaced the 1,500uF capacitor and it worked fine for a while.

ater on it started to degrade again. By touching the PCB I could positivele determine that it has to do with cold solders.

I disasemble the entire board from its chassis and touched up most of the pads. When I reinstalled it - it turns OFF after few seconds......

Even worse than before. Now it does not work at all..

Just wonder - where I can get such power supply and what is the expected cost ?

Thanks
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