samsung PS42C450B1WXXU

[lakey35]

Hi I have been having problems with my plasma tv and am stummped as to the solution so thought I'd try a pick a few brains on here.
When I plug it in the relay on the power board clicks then I can hear a faint ticking sound on the board.
I get no picture or sound.
If I disconnect the suppply lead from psu to z board the ticking doesn't happen and I get sound.
I am guessing that its a faulty cap somewhere on the psu but am struggling to find which one(s).
It appears as a fault with the vs supply but don't know what voltage I should get.
Any help please.

[PlainBill]

Re: samsung PS42C450B1WXXU

I can't find the service manual for this TV. The service manual and training manual for a similar set is here. There should be a white label on the back of the plasma panel listing the voltages.

The fact that the ticking sound stops and you get sound when you disconnect the z board suggests the Z board is bad; that is a common troubleshooting technique.

And it bears mentioning that pictures help us help you.

PlainBill

[lakey35]

Re: samsung PS42C450B1WXXU

Have found the voltages on the back of the screen thanks.
Used multimeter to check voltage values and they are gradually dropping from Vs 207 down to zero when tv turned on.
Have replace y board and still same fault.


As you can see the power connector to the y board is top left of 2nd pic.

[tom66]

Re: samsung PS42C450B1WXXU

Fixed this same TV. Failed Z-sustain.

Unplug the power connector to the Z-sustain. If TV powers up (with no picture or a very dim picture) and with sound then the Z-sustain is failed.

A particular MOSFET which is nearly impossible to source tends to go short circuit on the Z-sustain. The ticking is the PSU in protection mode.

[lakey35]

Re: samsung PS42C450B1WXXU

Do you know which mosfet please m8 as have a spare power board with a different fault I can rob parts from. Thanks

[tom66]

Re: samsung PS42C450B1WXXU

Do you know which mosfet please m8 as have a spare power board with a different fault I can rob parts from. Thanks

Not off hand. I think it's got two leads vertical and one going outwards and it's on the lower side of the heatsink. But you could test each individually until you found a faulty one.

I do have a failed Z-sustain board from that very same TV that you might be able to make use of as there are two of those MOSFETs on it and only one is failed. I would let you have it for £5.

[lakey35]

Re: samsung PS42C450B1WXXU

Sorry It's not the z-sustain board that has a fault. It's on the y board side on power supply. Even with y board disconnected the vs voltage drops from 204 down to 0. The supply for z-sustain comes of the y board on this model.
I believe the problem is on the power board but am struggling to find where.

[tom66]

Re: samsung PS42C450B1WXXU

Here's how I would tackle it:

Unplug Y and Z boards.
Plug in, press power button. Should make Samsung chime/melody (alternative - if you've turned this off, try connecting it to a source, or an antenna.) If so, problem is in Y or Z. If no chime, then bad power board (see below)

Connect Y board.
When turning on, does it make chime? If so, problem is in Z board.
If not, disconnect buffers from Y board. Does it make the chime now? If not, bad Y buffers. If it still doesn't chime, it's probably the Y.

If both Y and Z unplugged cause a problem then it's probably a PSU problem... but I haven't seen a PSU failure that gives power for a couple seconds, then shuts down... and I would suspect the main board or control board.

[lakey35]

Re: samsung PS42C450B1WXXU

When I disconnect the Y board I get the chime.
But the voltage vs still drops away to zero. All other voltages are present and remain at correct values.

[tom66]

Re: samsung PS42C450B1WXXU

When I disconnect the Y board I get the chime.
But the voltage vs still drops away to zero. All other voltages are present and remain at correct values.

That might be a protection feature. With no load (Y board) connected, the power supply could hold a high ~200VDC on its filter cap (by memory, 150uF 250V.) And being shocked by the Vs voltage is extremely painful, perhaps even dangerous or fatal. The power supply is capable of 1.5A on that rail. It takes merely 30mA to grab you (and stop you from releasing) and about 100mA to fibrilate the heart - 15x less than the supply is capable of.

The control board is probably noticing the Y sustain is not working and telling the PSU to turn that rail off (which is generated by a seperate section of the supply, because generating low 5-15VDC logic voltages on the same trafo as 200VDC is tricky.)

Your results so far do not match my problem, so I can't offer advice there, but would advise you try disconnecting the buffer (with the Y board powered), and seeing if it powers up.

[lakey35]

Re: samsung PS42C450B1WXXU

Have tried a different y sustain board and still does the same thing.
Also have tried a different z-sustain, control and main boards still the same result.
Could really do with a schematic of power board to trace vs and va voltages.

[tom66]

Re: samsung PS42C450B1WXXU

Have tried a different y sustain board and still does the same thing.
Also have tried a different z-sustain, control and main boards still the same result.
Could really do with a schematic of power board to trace vs and va voltages.

The power supply is MOST LIKELY FINE! Any voltage from it, even if it persists only for a few seconds, is a good sign.

Try disconnecting the control connector from the Y board as well as the power connector. Then the voltage might remain stable, but no guarantees.

Also, did you try disconnecting the buffer? The fact that both boards do not work seems to indicate something common to them - like the buffer board.

[lakey35]

Re: samsung PS42C450B1WXXU

Have tried disconnecting the control connector and still same fault. Have tried with buffer disconected and still the same.

[tom66]

Re: samsung PS42C450B1WXXU

Have tried disconnecting the control connector and still same fault. Have tried with buffer disconected and still the same.

Can you post a picture of the power connector on the Y board?

[lakey35]

Re: samsung PS42C450B1WXXU


Power connector is the top one, lower one is to connect z board

With the leads connected

[tom66]

Re: samsung PS42C450B1WXXU

Very blurry and hard to see anything, but use your meter to test the resistance between the Vs and GND, and Va and GND pins.

[lakey35]

Re: samsung PS42C450B1WXXU

o/c Va - gd
vs - gd slow increase till o/c

[tom66]

Re: samsung PS42C450B1WXXU

101.4k Va - gd
vs - gd slow increase till o/c

Okay, unexpected readings - now can you post a picture of the bottom of the Y board?

Oh - forgot - try Vs to Va.

[lakey35]

Re: samsung PS42C450B1WXXU


now getting o/c both va - gd vs-gd
va - vs o/c

[lakey35]

Re: samsung PS42C450B1WXXU


I take it you wanted a pic of bottom connecter to control board?