Samsung UA40D5000PR Pulsing output voltages

[scottsman76]

Hi Guys

I Have this Samsung smart tv that needs repair.
with everything connected i get pulsing A5V at the PSU connector. if i unplug the main board then all voltages pulse on the output connector.
I dont get any voltage on the LED connector.
there is also an audible click around the mosfet marked below
The connector to the Buttons all voltages pulse (3v)

I have searched and found a similar problem but there was a stable 14v, but was also not repaired.

I checked and replaced the mosfets with no effect.
Any ideas where i can start looking would be very helpful.

[nomoresonys]

Re: Samsung UA40D5000PR Pulsing output voltages

Simple crap first, heat up the electrolytic caps on the powerboard for a couple few minutes, then try the tv, see if there's any change, don't wait til it cools down, try it while it's still hot. Also check over the solder joints very closely, reflow any that look suspect, examples of bad joints there: https://www.google.com/search?q=bad+...ih=607&dpr=1.5

[nomoresonys]

Re: Samsung UA40D5000PR Pulsing output voltages

If you didn't already, with tv unplugged from power, unhook everything from the powerboard, mainboard, backlights etc, then plug power cord in and check those voltages again.

[scottsman76]

Re: Samsung UA40D5000PR Pulsing output voltages

I have unplugged and retried a few times with the main board and backlights in and out.
I get different readings, with everything in i dont here any noise from the mosfet area and solid 300 on the lower mosfet but nothing on the top one.
then i also only get pulsing A5V. nothing else.
With all pugs removed i get pulsing on all measurements on the connector to the main board. I also get pulsing on the led connector.

Ill try warming up the caps and see if get any difference.
I dont see any bad joints under close inspection.

[Davi.p]

Re: Samsung UA40D5000PR Pulsing output voltages

Hi, locate on the secondary the diode where it connects to the A5v output then desolder the central pin, connects to that central place an external 5v then test the board itself for the outputs, if the 5v pulses again disconnect the secondary electrolitic caps to the a5v rail and test again..

[R_J]

Re: Samsung UA40D5000PR Pulsing output voltages

Start by replacing the small electrolytics around the standby ic, CS806,CS804,CP811, see if that gives a stable standby A5V
CS804 is the startup/vcc cap for ICS801s, CS806 and CP811 are on the M_VCC line that supplies the pfc ic as well as the main ICM801 when the power supply is turned ON.