Samsung LE52M87BD Backlight

[pmurdoch]

Hi All
I have been tasked with repairing the above TV. The symptoms are powers on ok, have audio but cannot see an image. Prior to this I had replaced the caps on the psu as it had the usual turn on fault. All was good for 2 weeks. Now I have this problem. I cannot see the backlight glowing at all with the back panel removed. I have tested the transformers on the distribution boards and they all appear ok. I have tried to measure the output from the inverter on the Power supply board but I don't get anything other than millivolts. Certainly not the 1.7Kvolts that is stamped on the board. Is that because there is no load or am I missing the point completely.
Any assistance would be really appreciated as this is in a pub and what with the world cup and everything I am being hassled to fix it
Many thanks
Paul M

[selldoor]

Re: Samsung LE52M87BD Backlight

Its lucky there was no power on the inverter transformer, had there been it
would have probably burned your meter!
First check all your connectors unplug and replug
Pictures might help - please post using manage attachments jpg less than 3mb should be ok. top and bottom of the power supply. and one of the back showing the general layout.

Here is a schematic better virus test it after download - my russian isnt
http://archive.espec.ws/redirect.php?dlid=27082
Sorry doesnt work??? instead google this:
Скачать схему samsung_le52m87bdx_lcd_sch
and it will bring up the page with the link on.
Dont try to translate it - if you do the link doesnt work either.

[pmurdoch]

Re: Samsung LE52M87BD Backlight

Hi selldor.
I don't think my meter would have suffered. One lead on chassis and other one side of output.
Auto range would have cut in after 1000 volts. Anyway.
I have tested some more and have found that I have 5 volts on inverter on/off on PSU. I have also tried a ccfl on the inverter output and no joy.
Images are a problem from my tablet. Will keep trying
Many thanks
Paul.

[pmurdoch]

Re: Samsung LE52M87BD Backlight

Images as requested.
Many thanks
Paul
OOps.I have no idea why one of them is just terrible. Will try and get an overall picture later

[pmurdoch]

Re: Samsung LE52M87BD Backlight

Hi Selldoor
Forgot to say thank you for the schematic. It helps but unfortunately there is no info on the inverter. That's just typical.
Paul M

[tom66]

Re: Samsung LE52M87BD Backlight

The inverter is not really an inverter. It is a ballast, it just splits out the drive current to each bulb. If there is no high voltage in, then there will be no light from the bulbs.

If you have an old energy saving light bulb you can put it near the HV output on the power supply. If it lights up HV is present.

[pmurdoch]

Re: Samsung LE52M87BD Backlight

Thanks tom66
I have tried with an energy saver but there was nothing from the transformer on the power board. I have since bitten the bullet and purchased on customers behalf a new power board. Probably a lot better for me and him. It wasn't very expensive and it will save me hours of diag time. I'll report back when it is fitted.
Many thanks
Paul