Samsung LN32C450 - Audio but no video

[newtothis]

Re: Samsung LN32C450 - Audio but no video

Well that was correct, but now all of a sudden after unplugging the AC for a while it went back to turning on the backlight when the PSU-Main cable is D/C.

The symptom that I've seen change is that upon turning off the TV it now flickers the backlight once, then stays dark.

Is this with the PSU - MAIN connector plugged in?

[Aulus]

Re: Samsung LN32C450 - Audio but no video

Is this with the PSU - MAIN connector plugged in?

Yes. With the PSU-MAIN connected and wire #4 D/C, the flicker occurs on powering down.

[tom66]

Re: Samsung LN32C450 - Audio but no video

Hmm, in the user menu, you will have to use bright light, but try turning the backlight setting up to either full bright or minimum brightness, does it have any effect on behaviour?

[Aulus]

Re: Samsung LN32C450 - Audio but no video

Hmm, in the user menu, you will have to use bright light, but try turning the backlight setting up to either full bright or minimum brightness, does it have any effect on behaviour?

Ran the both the backlight and the brightness from 0 -> full. No change. Tried this with BUL_ON (Wire #4) connected and disconnected. No change.

[Aulus]

Re: Samsung LN32C450 - Audio but no video

Any more thoughts on where to go from here?

[tom66]

Re: Samsung LN32C450 - Audio but no video

There is a large, 450V yellow capacitor in the middle of the power board. With your multimeter set to the highest DC range, what voltage do you measure across it? Caution: high voltage, expecting around 390V. Do not touch any multimeter probes and avoid shorting them together or you could damage the power board. Test to be done with TV plugged in and powered on.

[Aulus]

Re: Samsung LN32C450 - Audio but no video

TV plugged in: 160V
TV plugged in and powered on: 384V

[Aulus]

Re: Samsung LN32C450 - Audio but no video

Any thoughts on what I can try next?

[tom66]

Re: Samsung LN32C450 - Audio but no video

That voltage is normal. Can you check if you have good 24V going to the inverter board? To test, put your multimeter red probe on each of the pins going to the inverter and black probe on chassis, noting the voltage.

[Aulus]

Re: Samsung LN32C450 - Audio but no video

That voltage is normal. Can you check if you have good 24V going to the inverter board? To test, put your multimeter red probe on each of the pins going to the inverter and black probe on chassis, noting the voltage.

I'll list the pins and their corresponding voltages:
1 - E-PIN: 1.0
2 - NC: 0
3 - BLU_ON: 5.1
4 - INV_ERROR: 1.6
5-9 GND
10-14 - B24V: 28.5V

Probably means nothing, but just something I experienced: When I unplug the AC plug from the back of the TV the blacklight flickers on/off but when I power down the TV through the front panel it does not.

Anyway, do you see anything peculiar in these voltages?

[Aulus]

Re: Samsung LN32C450 - Audio but no video

Thoughts on the next step?

Also, thanks for your help thus far. It's been a learning experience and quite entertaining

[tom66]

Re: Samsung LN32C450 - Audio but no video

Please double check 24V because 28.5V is much too high.

[Aulus]

Re: Samsung LN32C450 - Audio but no video

Please double check 24V because 28.5V is much too high.

Keep getting 28.5V. Done this on three separate days both on the inverter and PSU boards.
Is there a way to test if my multimeter is calibrated correctly?
It's new, on the 200VDC setting, so maybe it's not as accurate for 24V? Can't use 20VDC..

[tom66]

Re: Samsung LN32C450 - Audio but no video

Test a fresh AA battery, 1.5V expected.
A high 24V can cause the inverter to shut down, so this can cause your fault. Typical operational limits are 22.5V to 26.5V.

[Aulus]

Re: Samsung LN32C450 - Audio but no video

On 200VDC it read spot on for the AA Battery.. 1.5V

[tom66]

Re: Samsung LN32C450 - Audio but no video

Referring to schematic,


the B13V is unregulated, which is typical. This means if the 24V is out, the 13V should be out by a corresponding amount, in most cases. The 24V is labelled 24.5V nominal, which is more or less typical. If it is giving 28.5V, I would expect around 14.5~15V on the 13V outputs. Do you observe this?

I also notice this PSU incorporates overvoltage protection which should fire at around 27V + ~1.5-2V = 28.5-29V on 24V so the PSU is very close to cutting out.

[Aulus]

Re: Samsung LN32C450 - Audio but no video

The 13V is reading 14.2V.

[tom66]

Re: Samsung LN32C450 - Audio but no video

Hmm, that is quite high. Maybe not quite as high as expected, but a lot higher than the normal ~13.5V that a Samsung operates on. This could be the cause of the fault.

Can you see a device labelled "ZDTM851" on the top side of the power board? It should be near PC803S device.

[Aulus]

Re: Samsung LN32C450 - Audio but no video

Hmm, that is quite high. Maybe not quite as high as expected, but a lot higher than the normal ~13.5V that a Samsung operates on. This could be the cause of the fault.

Can you see a device labelled "ZDTM851" on the top side of the power board? It should be near PC803S device.

I found it on the under side, but cannot find it on the top side. Here's where the chip is at: Top left part of the board and just 1/8" up-left of the plastic support post. Should I be able to trace it or what do I do?

This can be seen on the psu board picture in the original post. Also notice that the camera flash shows the board as shiny. Not sure what caused this, but the top left portion of the psu board has this shiny look to it, with the edge of the board actually showing mold spots.

[Aulus]

Re: Samsung LN32C450 - Audio but no video

Also, retested the 24V wires with the backlight ON. I did notice a difference: 27.1V instead of 28.4V with the backlight OFF.