SCEPTRE U550CV 2.5v standby... (should be 5)

[dentheman]

All components look OK (nothing burned or leaked). The STB measures around 2.5v instead of 5... Any suggestions? Thanks




https://www.dropbox.com/s/eaw4nuebcpkbo2z/top.jpg?dl=0
https://www.dropbox.com/s/idjb781hg1...ottom.jpg?dl=0

[budm]

Re: SCEPTRE U550CV 2.5v standby... (should be 5)

In this case STB = PS-ON (PWR-ON).
Your pictures are not clear enough for me to read the pin names, please provide the pin name and follow by the DCV reading for each pin so we can easily see the data for each pin.

[tom66]

Re: SCEPTRE U550CV 2.5v standby... (should be 5)

Double check your multimeter battery & check against known working reference (e.g. fresh AA battery measuring 1.5-1.6V)

[budm]

Re: SCEPTRE U550CV 2.5v standby... (should be 5)

STB shows 2.5V (<1V = Power supply OFF, >2V = Main power supply ON) because it is the control signal not 5V STBY power supply output.

[dentheman]

Re: SCEPTRE U550CV 2.5v standby... (should be 5)

Here are some more pictures.

https://www.dropbox.com/sh/clan9c2fb...1DqlB8Tga?dl=0

More info:
Obviously - the power supply doesn't work. No standby light on TV, it doesn't turn on. The pin is 5VSB and it has 2.5v on it. Fluctuates between 2.3-2.6.
Also, I've bought a similar PS (from different Scepter TV model). Similar enough to use it for reference measurements (same pins) - the same pin shows good 5v

[budm]

Re: SCEPTRE U550CV 2.5v standby... (should be 5)

If you disconnect the cable between power supply pin and the main board, will the 5VSB become stable?
It may have problem with startup/running caps (I can see C11, C29, the third I cannot see the designator) for the 5VSB in the hot side.

[dentheman]

Re: SCEPTRE U550CV 2.5v standby... (should be 5)

The board is fully disconnected from TV when I checked 5VSB (same for that reference board).

Caps look fine visually but I haven't desoldered any of then to check

[budm]

Re: SCEPTRE U550CV 2.5v standby... (should be 5)

Those small caps you cannot tell by just looking, you need to test the capacitance and ESR.
BTW, you did verify that the rectifier diodes on the cold side of the standby power supply are OK, correct?

[dalilama]

Re: SCEPTRE U550CV 2.5v standby... (should be 5)

All components look OK (nothing burned or leaked). The STB measures around 2.5v instead of 5... Any suggestions? Thanks

I just fixed this issue on my Sceptre 55". One of the diodes (either D10 or D11) are bad and the bridge rectifier circuit is only able to produce 1/2 of the required STB. You need SB5150 diodes to replace them. I replaced both but only 1 tested bad.