Samsung BN44-00516A no 5v Stby

[BigPete]

So I've done a lot of searching trying to figure this one out. I've replaced the usual faulty components on this board.
I've repaired a few of these boards already but never had this issue.
There's no 5v Stby or PS_ON voltage.
There's no voltage at ICP801.
I figure the standby circuit comes from the rectified circuit supplied through the resisters and diodes. Then goes to some Zener diodes and transistors to diode DM832, where the voltage output stops.
From there the circuit goes down to the optocouplers.
I swapped ICP801 and a few other bits and pieces with no change.
What I have done is bypassed the relay to force the TV on, which turns the TV on no problem. After that the TV will happily run, the standby circuit will operate fine, but once the TV is unplugged and the board discharges, the 5v standby doesn't return.
Could someone please point me into a direction of what to test next.
The board comes from a Samsung 64E8000 TV.
Thanks

[thommyX]

Re: Samsung BN44-00516A no 5v Stby

Do you have an error code?
Then remove the glue around ICX801, transition resistance. Check CS825 and QS804.

Thomas

[BigPete]

Re: Samsung BN44-00516A no 5v Stby

There's no ICX801. There's no error code. There's no power going to the main board to drive an error code.
Is ICX801 the same as US801? It's in the same vicinity as CS825 and QS804. US801 is a 8pin IC.

[R_J]

Re: Samsung BN44-00516A no 5v Stby

TX801s is the standby transformer, F802s supplies voltage to the transformer primary winding and then to the standby ic. This ic is covered in silicon on the top of the board
Do you have any voltage across CP803? if not check that the green ntc thermistor (NT801S) next to the relay is not open, it should be around 8~ 10 Ω

[BigPete]

Re: Samsung BN44-00516A no 5v Stby

Thank you for that R J.
NT801S was open.
I've now replaced it and the TV is back up and running.
Thank you again.
Cheers.
Pete.

[R_J]

Re: Samsung BN44-00516A no 5v Stby

When NT801s goes open it is because the relay contacts are bad, If you don't either clean the relay contacts or replace the relay the ntc will go open again.
If the ntc is warm when the tv is ON (not in standby) the relay contacts are bad.

In standby, only a small current flows through the ntc, when the tv is ON, the relay shorts out the ntc to prevent it from going open when the tv is drawing a higher current.

[BigPete]

Re: Samsung BN44-00516A no 5v Stby

Ok. I'll check that out. Thanks.