LG 50" Plasma

[Cornboats]

This set came in with blown fuses.
I've changed all four IPM's on Y-sus and Z-sus to be on the safe side.

Powered up straight away but I'm worried about the heat off z sus ipm's.

With digital temp probes sitting on the fins these are increasing from ambient to 40 deg c in 5 minutes. I bottle out after then for fear of the things blowing up again. IPM votage is 18.2 V.

Now the Y-sus is running much cooler 32 deg c in 5 minutes. Ipm voltage is 16.2V.

Has anyone got a working set on the bench to check temperatures for me. If not a 50" a 42 " should tell a similar story.

Also- connected an old analogue scope with x10probe to check wave forms. Can't seem to get anything like manual says I should.

Anyone have advice about scoping plasmas would be appreciated.

[PowerAmpFreak]

Re: LG 50" Plasma

When you say "IPM voltage" is 18.2V - is this verified according to levels in the service manual?
What picture do you have when you measure the temps? I would expect the Y-SUS to dissipate more heat when there's a bright picture. Could you measure the power drawn from the mains aswell.
Normally, in my experience, the Y-SUS heatsinks is most of the time hotter than the Z-SUS. Not much of a help, but more a clap on the shoulder!

[cadiman]

Re: LG 50" Plasma

I have had y board ipms running at 140*F. The Z drive was always cooler, but I would expect it to run around 80 to 100*F on the L/Gs

I have had transformers on power supply boards running at 120*F

You may need 300 mhz scope for plasma. I found a used one for 150.00
I have a good 100mhz scope and it is hard to chase down waveforms on some of these.

[Cornboats]

Re: LG 50" Plasma

Thanks for your reply.

The 18v was taken off the back of the boards.
ref 6871qzh044c-z sus
ref 6871 qyh039c-ysus

Its a puzzle to me why the Y-sus is 16.2V and is running cooler than the z-sus which I've re-read at 18.2.v.Picture was normal tv programme.

If you say the average working temp should be 80 -100f then I've got to be worried.

40c = 104F and I've been turning set off after 5 minutes so this temp is just going to climb if I leave on.

My scope is 50MHZ - No wonder I can't get any good pics then.


I'll take a power reading with my amp probe and come back with info.

[PowerAmpFreak]

Re: LG 50" Plasma

The heat generated by driveboards are powerdissipation caused by switching losses and conduction losses of the IPM powerswitches.
As long as you have sufficent gate-drive levels for the IPM switches, the magnitude of supply-voltage will have less effect on total heat dissipation.
The conduction losses increase with increased power throughput and switching losses occours each time the powerswitches go from off to on and then back.
I assume that you have already verified that all operating voltages, like Vs and Va, is properly trimmed according to the panel used and the service manual.

[Cornboats]

Re: LG 50" Plasma

Hi. Yes I set up vs,va,z bias, -vy and vsc as per label using dvm.

I can't check vsetup because my 50mhz scope doesn't seem to capture the wave form .

I took current consumption at the mains with tv picture on which is 4.2 amps based on my mains incoming at 229v ac.

From my distant past I recall power in wattts =V x I

therefore 229 x 4.2 =961.8 watts

That can't be right can it? The screens only rated at 400watt-full white.

[b700029]

Re: LG 50" Plasma

Drawing more than double the rated wattage? It sounds like something is partially shorted.