Samsung Plasma PN50C550G1F : no image, but sound is ok

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Update on the voltage for Ve...

I was about to remove the XMain to check for shorts, and realized it was disconnected ...

Ve starts at at 89V and ramp down to 0.
(The label says 83V), so not sure that to say about this...

Other measurements remains the same.

Vs on the PSU testpoint starts at its nominal value 212V for about 1 second, then ramp down to 0.

Va on the PSU testpoint starts at its nominal value 55V for about 1 second, then ramp down to 0.

Vscan on the Y-main testpoint starts at its nominal value -190V for about 1 second, then ramp down to 0.


So should I check for shorts on Xmain anyways, or is there something else to look for?

[tom66]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Please remove the X-main board and check it for shorts. Check transistors on the heatsink for shorts.

$40 is a good price if the boards are ok

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

BTW, I have seen a kit of boards (Y-main, Y-buffer, X-main) for about 40USD near my place on ebay.

If there's a good chance the probelmatic board is one of them, it might be worth to get them...

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

The LVDS I have disconnected is the one shown in picture

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

All right,

I have disconnected the really thin flat data cable connecting the logic board to the A/V board (LVDS cable).

I have disconnected the ribon cable between the PSU and the A/V board, and added a pull down (80 Ohms) on the PS-ON pin.

I added a jumper on the diag connector of the logic board (pin 3 and 4).

As soon as I turn the power bar on which the TV is plugged in, the power supply turns ON (It clicks like when I press the power button when everything was connected).

The logic board still go in its protect mode (led flashes 5 sec ON, 2 seconds OFF).

Vs on the PSU testpoint starts at its nominal value 212V for about 1 second, then ramp down to 0.

Va on the PSU testpoint starts at its nominal value 55V for about 1 second, then ramp down to 0.

Vscan on the Y-main testpoint starts at its nominal value -190V for about 1 second, then ramp down to 0.

Ve on the X-main testpoint starts a 0.40V and ramp down to 0.36V.
(But label says value should be 83V)

Jay

[tom66]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Yep that's the one.

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

It's a little four pin connector, 0.1" spacing, square in shape and should not be connected. Vetical. Pins marked 1, 2, 3, 4. There may be another connector but don't use that as it's probably the programming header.

Thanks Tom66 for the clarification... At first, I thought you were talking about that programming header connector. I have located the 2x2 diag connector as shown on the picture.

i'll install the jumper on it and also on the PS-ON pin of the connector and run the tests and report the results.

[tom66]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

So I only have to ground (or pull down with a lower resistor) the PS-ON pin of that connector. I leave all other pins open right?

Correct.

Just to make sure I'm not mixing names again:
- main board = A/V board (the one with the hdmi and other connector)
- control board = logic board

Yes, and the control board is the smallest one, usually below the power supply

The diag connector is the CN2011 connector (the only one that isn't connected by default) on the logic board right?.

It's a little four pin connector, 0.1" spacing, square in shape and should not be connected. Vetical. Pins marked 1, 2, 3, 4. There may be another connector but don't use that as it's probably the programming header.

Or you want incremental trials
1 - gnd PS-ON pin
2 - gnd PS-ON pin AND disconnect LVDS cable
3- gnd PS-ON pin AND disconnect LVDS cable AND add jumper (3-4)

Please try only (3) for now.

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

You might need a lower resistor than 1k.

So I only have to ground (or pull down with a lower resistor) the PS-ON pin of that connector. I leave all other pins open right?

You may also need to disconnect the LVDS cable (between the main board & control board)

Just to make sure I'm not mixing names again:
- main board = A/V board (the one with the hdmi and other connector)
- control board = logic board

and jumper pins 3 & 4 on the control board diag connector to activate the test patterns mode

The diag connector is the CN2011 connector (the only one that isn't connected by default) on the logic board right?.


Do you want me to do all of these in 1 trial:
- gnd PS-ON pin, disconnect LVDS cable and add jumper 3-4

Or you want incremental trials
1 - gnd PS-ON pin
2 - gnd PS-ON pin AND disconnect LVDS cable
3- gnd PS-ON pin AND disconnect LVDS cable AND add jumper (3-4)

I'm leaving for beakfast, so I'll try this when I come back.
Thanks again for your time (and patience)

[tom66]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

I am aware the control board will shut down but it needs to be done this way because some Y-main/X-main boards will not turn on the voltages until the control board sends the right commands.

You might need a lower resistor than 1k.

You may also need to disconnect the LVDS cable (between the main board & control board) and jumper pins 3 & 4 on the control board diag connector to activate the test patterns mode, which will force it to generate control signals even if the main board does not send the right commands.

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

just a side note...

When all boards are connected, the Vs, Va, Vscan starts at their nominal values, but decrease to 0 when the logic board puts the power supply in protect mode.

The Ve on the Xboard, remains steady at a 0 flat all the times. So that one doesn't seem to behave like the others...

I have tried to force the power supply to ON by adding a pull down on the pin PS-ON of the cable CN801 (A/V board) (1k resistor between the PS-ON pin and gnd pin as show in picture attached in previous post), but it doesn't wake up the power supply. Not sure If I need to add a pull up/dn on other pins such as Standby or if the wake up is not a fixed pulldn, but rather a temporary "pulse" to emulate a button press. If you an tell me how to turn on the power supply when the main A/V board isn't connected ... It would be appreciated.

Thanks
Jay

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

image of where I would install the pull down to bypass the A/V board since it would be disconnected (force the power supply to on).

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

A/V board should *NOT* be connected, use resistors in place of it to turn on power board.

Connect logic / control board (small green board below power board) for these tests.

The A/V board and main board are two names for the same thing. The logic / control is separate from the main board.

This is not where I use the 2 resistors on my previous trial...

On the connector CN801 (that connect the PSU to the A/V board, there's no VS-ON pin, only the PS-ON pin). So you want me to install a pull down on the PS-ON of the CN801 connector (by using a 1K resistor between it and a gnd pin as shown on the picture)?

The logic board might still detect a problem and still generate the protect mode (led blink 5s on, 2 s off). If this is the case, the Vs will not be generated and so is all the others voltages...

The only way I was able to generate a steady Vs out (and Va and others), was when the logic board was disconnected and when I was using pullup/pulldn on the VS-ON and PS-ON ...

I just want to make sure I understand the testcase you're talking about ...

[tom66]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

A/V board should *NOT* be connected, use resistors in place of it to turn on power board.

Connect logic / control board (small green board below power board) for these tests.

The A/V board and main board are two names for the same thing. The logic / control is separate from the main board.

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Ok, can you check Ve on the X-main?

will also check the Ve on the X-main board too using the same setup (using jumper to bypass the logic board).

Thanks for your help...

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Yes please do that, and check VS/VA too. The cable between power board and main board should be disconnected and the jumper resistors should be in place.

Ok I try this later tonight (leaving for family diner) and report the results...

So it will be :
y-sustain connected (CN804)
A/V board connected (CN801)
main board not connected (CN802), but using jumpers to force Vs drivers.

An measure the Vs, Va, Vscan lines

[tom66]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Ok, can you check Ve on the X-main?

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

When I connect the CN804) (all boards are connected), the VSCAN (VSC) behave like the others voltage lines : it starts at its nominal value (-190VDC) and then ramp down to 0VDC in about 20 seconds.

[tom66]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Yes please do that, and check VS/VA too. The cable between power board and main board should be disconnected and the jumper resistors should be in place.

[superbigjay]

Re: Samsung Plasma PN50C550G1F : no image, but sound is ok

Y-main = Y-sustain

VSCAN and VS are different. VSCAN and VSC are the same.

Ok,

On the testpoint VSC, the voltage is 0.
But as I said, like it is setup right now, the Y-sustain is not given power by the power supplu (CN804 is unplugged).

So I guess, you want me to connect the CN805 cable and see if it receives VSCAN voltage at all?

If I do, then all cables will be connect, because Y-sustain board is the only one that is unconnected right now.

Jay