LG Plasma 50" TV repair (Model: 50PS6000)

**bodeplot** · 20-03-16, 10:44 PM

I repaired this unit for a coworker - an LG Plasma 50" TV (Model: 50PS6000) This isn't my line of work now days, but like to keep the skills sharpened in case I return to the service industry. It's my first plasma TV repair. Since there is no repair history on the net about this model, I figured I would start here

. Picture of unit below:

This unit would power up for 2 seconds, then power down. Relays could be heard energising (clicking) and then de-energising. No life on the screen. Without pulling the covers off, it looked like a short out.

Covers off, I isolated the power supply board and powered on. Fault had not changed, so investigated the power supply board. This is a very sophisticated power supply that has a power factor correction feature.

Chopper MOSFETS W20NK50Z (Q802 and Q801) in the switch mode section of the P/S were short. A slow blow fuse T4A H250V powering them (F801) also blown. See pic of PCB below, the components are removed, yellow squares indicating component locations:

The faulty bits:

Flipping over the board, the high voltage resonant controller (switch mode IC) L6999 (IC801) had also been taken out by the chopper transistors.

Replaced all four components from RS Components for under $40.

2 x RS Stock No. 486-3114 STMicroelectronics STW20NK50Z N-channel MOSFET Transistor, 17 A, 500 V, 3-Pin TO-247
Packet RS Stock No. 541-3798 Cartridge Fuse, T, 4A, 250 V ac
Packet RS Stock No. 167-6018 Fuseholder 5x20mm OGN 10A
1 x RS Stock No. 686-5011 STMicroelectronics L6599D, Resonant Controller, 16-Pin, SOIC

I also reflowed the area indicated by the magenta box in the above pic. There were lots of dry joints. This appliance not so lead free now

I think the source of the problem is lack of support for the power supply board. Other boards in this unit have support in the middle of the board. For some strange reason, the power supply board doesn't. It's a very heavy board which is prone to flex, and with the crappy solder used, and all the surface mounted electronics on the back of the board, it's a recipe for an early failure.

The owner said this unit was faulty for a long time. He hadn't got around getting it fixed, so it faulted within a few years of ownership. It had also been transported a lot since ownership, face down. So, I reckon all that flexing of the board during transport damaged the soldering on this board, causing the eventual failure.

I recommended to the owner to never to transport TV face down, or even better, don't transport it at all !

Regards,

J

**Rick** · 21-03-16, 08:35 AM

Top post thanks for sharing

**best4less** · 21-03-16, 06:57 PM

I have done a few of the same repairs but after a couple I found the odd one would fail again
due to the Z or Y board dragging the supply voltage down and in turn cooking the components again

I hate fixing Plasma TV's for this exact reason

But still that is a great post and thanks for the share

**bodeplot** · 21-03-16, 11:57 PM

The last TV repairs I did commercially was back in the days of cathode ray tubes, so I'm a newbie with this tech.

Could you explain Y and Z boards ?. Is this for the LG range of TV's ?

Nb/ I did a few google searches about Plasma tech before I did the repair. All I could get was an overview. ie: A grid of neon bulbs powered by two screen voltages and a ground.

Cheers J

**TVguy** · 22-03-16, 11:01 PM

Originally Posted by bodeplot

The last TV repairs I did commercially was back in the days of cathode ray tubes, so I'm a newbie with this tech.

Could you explain Y and Z boards ?. Is this for the LG range of TV's ?

Nb/ I did a few google searches about Plasma tech before I did the repair. All I could get was an overview. ie: A grid of neon bulbs powered by two screen voltages and a ground.

Cheers J

The Y and Z sustain PCBs are common to all PDPs. PDPs are purely digital displays; i.e. thay are either fully lit or in a ready state for discharge.
The display is generated by a series of sub-fields of differing sustain times to allow for a grey scale. Think of the image intensity being pulse width modulated.
Perhaps may help in shedding some light on the product. It describes a USA model of a similar vintage with what appears to be the same PSU.
PFC has been mandated by the regulators for any product exceeding 90 Watts (television fall into this category).
Unfortunately PDP has been killed off by the energy regulators and is sadly now a part of history.

**bodeplot** · 23-03-16, 08:48 PM

Thanks TVGuy for the info. The model I repaired had two power control boards that supplied power to the screen. The first one was easy to work out, as it had lots of IC's on the board and the power supply/control to the screen had lots of lines (via kapton ribbon). The other wasn't as easy to work out. It had a common rail supplied to the screens via kapton ribbon. I was wondering if this common controller is a return, or does this supply a separate voltage/pulse ?

Cheers J

**TVguy** · 24-03-16, 10:40 PM

Originally Posted by bodeplot

... The other wasn't as easy to work out. It had a common rail supplied to the screens via kapton ribbon. I was wondering if this common controller is a return, or does this supply a separate voltage/pulse ?

The LV drive voltages from the sustain PCBs work from a floating ground. This is necessary to isolate the high voltage discharge from the delicate Control Board.
The Y-Sustain PCB generates non-ground referenced high voltages. I have had the displeasure of brushing my bare arm against the heatsinks on the Y-Sus PCB whilst touching the main earth.