Bn44-00514a psu no stby

[krygods]

I have a PSU P/N BN44-00514A from a Samsung PN60E7000 that has no standby voltage.

Wondering if someone could help me troubleshoot this PSU as there are no replacements available so this is all that I have to work with.

I've tested QP802 QP804 as well as QS802 QS804 all seem to test good if I'm testing them correctly. DMM on diode mode, black lead to drain, red lead to source, touch red lead to gate, and then red lead to source again. Is this the correct way to check N channel MOSFET?

DP802 tests good.

All diodes test good.

Both fuses test good.

CP801 CP802 CP803 all show 160VDC

[krygods]

Re: Bn44-00514a psu no stby

I just put the PSU back in the TV and now there is 3.2VDC at PS_ON and 0.54VDC at STBY

[krygods]

Re: Bn44-00514a psu no stby

TV does nothing no standby light

[ReeceyBurger123]

Re: Bn44-00514a psu no stby

How does the standby look with the Mainboard unplugged ?

[krygods]

Re: Bn44-00514a psu no stby

with the mainboard unplugged PS_ON is showing 3.8VDC and STBY is showing 0VDC

[freakaftr8]

Re: Bn44-00514a psu no stby

On this power supply QS804 controls standby. Black lead to center pin red lead on each outside pin.

[budm]

Re: Bn44-00514a psu no stby

There are many threads on this BN44-00514:
https://www.badcaps.net/forum/search...archid=5501182
The standby switching power supply is working but the switched POWER MOSFET QW880 (SMD) is not turn on to supply the DCV to the STBY pin. You should have DCV between the two legs of the cap CX857.

[krygods]

Re: Bn44-00514a psu no stby

There is 5.3VDC between the legs of CX857

The power mosfet QW880 if i'm looking at the right part is marked QM880 I believe and the P/N is AO4184. Is it common for this part to fail? I have three extra of these parts that I ordered a while back for another similar power supply.

[budm]

Re: Bn44-00514a psu no stby

Yo need to check the DCV between G and S pins, more likely it is not being turned on.

[krygods]

Re: Bn44-00514a psu no stby

Showing only a few mV between G and S.

[budm]

Re: Bn44-00514a psu no stby

It is not being turned on, you have to trace out the Gate pin to see where it goes to, I have a hard time tracing out using the pictures.

[krygods]

Re: Bn44-00514a psu no stby

Ok I shall attempt to trace the gate pin if I have trouble I'll get out the tripod and camera and attempt to take hi-res pictures.

[krygods]

Re: Bn44-00514a psu no stby

This where I'm at so far.

[budm]

Re: Bn44-00514a psu no stby

Check the DCV between 'A' and 'GND'.
Also need the values of those two resistors as marked in the red box.

[krygods]

Re: Bn44-00514a psu no stby

DCV between 'A' and 'GND' is 26.75V

RX881 330 ohm (331 Marking) measures 325.8 ohm
RM882 33 ohm (330 Marking) measurement starts at 140 Kohm and steadily rises. This resistor is bad?

[budm]

Re: Bn44-00514a psu no stby

That RM5882 (33 OHMS) looks to be the one that supplies the bias Voltage for the QM880
So the RM882 shows as 33 Ohms?
Check the DCV between 'B' and 'GND'.
Check the DCV between 'C' and 'GND'.
Check the RESISTANCE between 'C' and 'GND'.

[krygods]

Re: Bn44-00514a psu no stby

Sorry I edited the last post with the measured values.

RM882 measures 140 Kohm and steadily rises.

[budm]

Re: Bn44-00514a psu no stby

OK, you need to check that resistance 'Check the RESISTANCE between 'C' and 'GND'.'

[krygods]

Re: Bn44-00514a psu no stby

DCV between 'B' and 'GND' is 4.36V

DCV between 'C' and 'GND' is 72mV

Resistance between 'C' and 'GND' is 107kOhm starts reading at 90kOhm and stabilizes around 107kOhm

[budm]

Re: Bn44-00514a psu no stby

DCV between 'B' and 'GND' is 4.36V

DCV between 'C' and 'GND' is 72mV

Resistance between 'C' and 'GND' is 107kOhm starts reading at 90kOhm and stabilizes around 107kOhm

The resistance is fine, I just want to make sure that CX806 (between GATE pin and GND is not shorted), for the 33 Ohms to burn out something is drawing lots of current. You should verify that the MOSFET is OK, check the resistance between GATE pin and SOURCE pin, GATE pin and DRAIN pin to make sure it does not show low resistance. That 'C' test point also go to other compoents beside the GATE pin.
You can try 47 Ohms resistor in place of 33 Ohms, then measure the Voltage drops across that 47 Ohms so we determine the current draw.