Westinghouse EW50T5KW no backlight

[speter]

I'm having a great week, I've checked my storage for a replacement TV to replace the 55" Vizio my daughter smashed, the first was the LG curved(panel failure?) then the TCL 55 (bad LED strips) The the Samsung 60" (shorted LEDs again) Now I'm looking at a Westinghouse EW50T5KW with a power supply problem. When it is plugged in all I get is the blue power light, I can't really see a picture with a flashlight, so I'm not sure if it is booting up
I have 5V & 12V with the LED connectors unplugged and BKon jumpered to 5v and PSon jumpered to VSb I only get 5v at the backlight connectors, sometimes the PS will slowly pulse as though it's being dragged down, with BKon jumped. without BKon jumped the 5v and 12v are rock solid.
I also have 5v and 12v with everything connected properly just plugged in.
Nothing burnt, or bulged, nothing gets warm. i have checked for shorts on almost all of the semiconductors, without seeing anything.

[speter]

Re: Westinghouse EW50T5KW no backlight

I think I found it, Q203 seems to be shorted, it is hidden under the heat sink by the control connector, something weird is the schematic says SOT, but it is a TO220 style case, the number is hidden, the whole heat sink has to come off to change the device.

[speter]

Re: Westinghouse EW50T5KW no backlight

I was mistaken, it ended up the"shorted" device was D204 which is 2 diodes which are strapped together in parallel , so no short there, I was finally able to read the number to verify it, so it was good after all.

[speter]

Re: Westinghouse EW50T5KW no backlight

I've run out of ideas on this one, there is no activity on the HV part of the supply, and I can't find anything open, pr shorted. I'm giving up on this one...

[R_J]

Re: Westinghouse EW50T5KW no backlight

You likely have a bad led string in the panel causing the led boost circuit to shut down. With the led's disconnected there will be no boost voltage due to no current being drawn. same as an open string.
Monitor the voltage across EC202 when the tv is first turned on.
Check if R151 is ok.
Check the voltage Across EC104, this is the PFC_Vcc

[dick_barton]

Re: Westinghouse EW50T5KW no backlight

What voltage do you have at LED_Vcc of Q102. With the power off, what is the resistance from LED_Vcc to HOT ground ( eg negative leg of EC101)
Check D1, D2, D3, D4 and D123 connected to T103

[speter]

Re: Westinghouse EW50T5KW no backlight

I am going back to it in a minute, I never see more than 5v across the LED strips or connectors, plugged in, or not, the caps upper right first pic, never charge. I'll get back with the other info shortly.

[speter]

Re: Westinghouse EW50T5KW no backlight

R151 reads .3 Ohms, no voltage across EC202, EC104 is .06v without BKon jumpered to 5v 1- 8V pulsing with it jumpered.
12v and 5v are also pulsing 40%? with BKon jumped, but solid when BKon is not jumpered. Q102 LED VCC is 5 - 9V pulsing with BKon jumpered, .05 when not.
Q102 LED VCC reads open to ground.
D1,2,3 and 123 check good, D4 is not used on this board
I found another thread on this board, or a very close cousin, I will read through that as well

https://www.badcaps.net/forum/showthread.php?t=54024
It seems as though when Q110 is turned on Vcc drops causing things to go crazy, Checking R109

[speter]

Re: Westinghouse EW50T5KW no backlight

Well. it wasn't R109...
It cycles drawing 0 then 19w repeating if Bkon is jumpered

[dick_barton]

Re: Westinghouse EW50T5KW no backlight

What voltage do you have across the two pins of EC101 and EC107 with and without Backlight jumpered?
I think the PFC is not working. PFC_Vcc should be typically 12V

[speter]

Re: Westinghouse EW50T5KW no backlight

EC101 pulses between 250-320v with BKon jumpered 161v not jumpered
Ec107 pulses between 4.5 and 8v with BKon jumpered 13.3 not jumpered
R135 never has voltage across it, so it's never trying to power T103
There is no voltage at pin 6 of u103 when BKon jumpered

[dick_barton]

Re: Westinghouse EW50T5KW no backlight

The 13V at VCC (EC107) looks good so with the set powered off what is the DC resistance of U102 between Vcc (Pin 8) to GND (pin 6)

With the power on and no backlight jumper what are the voltages at Q102 & Q110 emitter, base & collector.

[speter]

Re: Westinghouse EW50T5KW no backlight

Pin7 of u102 gives pulses of up to 1.5v, my meter is not very fast, so it could be higher. Bkon jumpered
The gate of Q103 has similar readings
Resistance between pin 6 and 8 is open
Q110 Ebc 13, .4, .3
Q102 voltage less than .5v on c and b, 0v on E Voltages start at .5, and drop as the ps is on longer

I wish I had FLIR, something takes 20W during the cycle
I soldered a bleeder resistor across EC101 so the PS resets faster during power tests.

[speter]

Re: Westinghouse EW50T5KW no backlight

Q103 is supposed to boost the voltage?

[nomoresonys]

Re: Westinghouse EW50T5KW no backlight

Maybe check resistor R250 and the rest, diode checking video, just for anyone looking on
that may need it: https://www.youtube.com/watch?v=BXOS5czCb3Q

[speter]

Re: Westinghouse EW50T5KW no backlight

It checks good, that whole area checks good, and is basically dead(voltage wise) always.
Thanks for the suggestion!

[nomoresonys]

Re: Westinghouse EW50T5KW no backlight

Maybe heat up your electrolytic caps with a hairdryer, can heat the ceramic caps too, see if the tv acts any different.

[budm]

Re: Westinghouse EW50T5KW no backlight

Are you getting about 380vdc PFC Boosted Voltage when TV is turned on or when the board is forced on?

[speter]

Re: Westinghouse EW50T5KW no backlight

When Bkon is forced on it attempts to boost, but only in cycles, it gets 250 - 320 in waves. and it drops 12v, and 5v while trying.
When BKon is not forced, no boost at all

[budm]

Re: Westinghouse EW50T5KW no backlight

When Bkon is forced on it attempts to boost, but only in cycles, it gets 250 - 320 in waves. and it drops 12v, and 5v while trying.
When BKon is not forced, no boost at all

That means you will need to fix the PFC boost circuit or find out if something else is causing the PFC not to function properly.