Norcent plasma PT-4291HD no display, unresponsive

[fuxxy]

Just picked up a Norcent PT-4291HD plasma from the dumpster.

Plug in unit, hear a "click"

Press power, hear a series of clicks.

No output from screen, no audio output

Afterward, unit is completely unresponsive, power button does nothing.

TV has a Samsung V4C power board. CODE: LJ44-00092E

Found about 5 fuses so far, one has tested open - F401

Also found a schematic of the power board that I've attached.

[tom66]

Re: Norcent plasma PT-4291HD no display, unresponsive

Where is F401 located?
Pictures, please...

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

closeups

[tom66]

Re: Norcent plasma PT-4291HD no display, unresponsive

Check the MOSFETs in that area for shorts -- if none found replace fuse & see if it pops. If not you probably just fixed the TV.

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

Are MOSFET's only found attached to heatsinks? Or could they be standalone?

[tom66]

Re: Norcent plasma PT-4291HD no display, unresponsive

Sometimes both. Most often though on a power supply, they are on a heatsink.

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

Also, Would it be best to remove the MOSFET from the board to test, or should it be okay to test while installed?

Wow, the schematic says IC401 is directly fed from F401's circuit. After finding IC401, It does appear that something's pulled more of a load than it should have..

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

According to the schematic:
Component - schematic value - actual value

F401 - closed - open
R401 - 100K - 100K
C401 - 2.2nF - unknown
D401 - BYV38 - .47V / inf.
R402 - 10ohm - 9.6 ohm
D402 - 1N4148 - .55V / inf.

As far as the IC401 (I assume that's the MOSFET)
Pins 1 and 2 are dead shorted. I removed the mosfet from the board, and there is another exact one on the heatsink I can compare to. IC401 is definately bad.
Schematic says it's a KA1M0880B, marking on the component is a 1M0880


go figure, they're obsolete - unattainable through mouser. Anyone else have a source for this?
EDIT: the interwebs suggest FS7M0880 as a suitable replacement

[tom66]

Re: Norcent plasma PT-4291HD no display, unresponsive

Umm, yep. There's the problem. The most important characteristics will be the switching frequency and the RDS(on). Switching frequency should be within 5kHz or so. RDS(on) should be the same or lower. This is a MOSFET + controller IC all in one.

[retiredcaps]

Re: Norcent plasma PT-4291HD no display, unresponsive

C401 - 2.2nF - unknown

Some multimeters can measure capacitance. If yours cannot, C401 should measure open when you try to measure its resistance.

Schematic says it's a KA1M0880B, marking on the component is a 1M0880

go figure, they're obsolete - unattainable through mouser. Anyone else have a source for this?

http://www.ebay.com/itm/120929094021

Stock up at $3 each. Shipping is $4 for the first and then 10 cents for each extra chip.

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

Update: TV is still dead.

Power Supply board is a Samsung V4C CODE: LJ44-00092E

I replaced IC401 with a FS7M0880TU

Also replaced F401 with a Littelfuse 3.15A TR5

Mounted the power supply board, plugged everything in, hit power, and results are same as before. A series of clicks, LED on front turns green, but no display at all.

A sticker inside the panel says
Va Vsc Vs Ve Vset
70 -190 204 84 195

Actual values with green LED lit on front:
Va Vscan VS Ve Vset
70.4 5.9mv 131.9mv 0.0 0.0

While I had the board out, I tested all the other fuses I could find. All were good.

I've attached a schematic of the power supply, as well as pictures of the component side.

Going to pull the board and check F401 to see if it blew. Anything else I should take a look at?

EDIT: F401 is still good.

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

It appears that VS powers VSET, VE, and VSCAN.

VS is low, so I'm going to direct my attention to that.

[tom66]

Re: Norcent plasma PT-4291HD no display, unresponsive

It's possible the other IC has failed too, but without obvious signs. Did you replace both?

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

I did not. The other ic is identical, labelled ic301. I can remove and test for short when I get home.

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

Measured regulator voltages with power applied and power button "on"

IC401:
Pin no.
1. 387VDC
2. GND
3. 17.91VDC
4. 6.61VDC
5. 1.74VDC

IC301
1. 113VDC
2. GND
3. 17.86VDC
4. 0.370VDC
5. 0.833VDC

Ive got no idea what I'm supposed to be getting, but it's strange that both chips are gettind different voltages supplied, when they're both powered with V_PFC going through the same mirrored circuit.

[tom66]

Re: Norcent plasma PT-4291HD no display, unresponsive

113VDC looks too low, please test it again to be sure.

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

113VDC looks too low, please test it again to be sure.

It's fluctuating, but definately 119-123 VDC

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

The only difference between the "feed" side of IC401 and IC301 is the transformer. Otherwise, the fuse, resistors, capacitors, and diodes are exactly the same type and value.
I have not started removing components on the IC301 circuit and testing values yet though.

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

I'm thinking of removing the swapping the transformer from the IC401 circuit and the IC301. I would only attach the primary winding though. I have no other way to test the transformer - Do you guys think that this would be a good idea?

[fuxxy]

Re: Norcent plasma PT-4291HD no display, unresponsive

UPDATE: Could not determine what was wrong with the old PSU, so I found a cheap replacement ($40) on ebay. Replaced the PSU.

Tested voltages for Va Vsc Vs Ve Vset with only the PSu plugged in, and got voltages that were WAY off. Plugged in the YSUS, ZSUS and backlight, powered the set on again, and boom, voltages are correct, and TV works.

Thanks for the help everyone!