Westinghouse EW50T5KW no backlight

[speter]

Re: Westinghouse EW50T5KW no backlight

I don't fully understand the operation of the power supply, so normally with PSon forced,
and BKon not, EC101 is supposed to have 380v on it?

[budm]

Re: Westinghouse EW50T5KW no backlight

I don't fully understand the operation of the power supply, so normally with PSon forced,
and BKon not, EC101 is supposed to have 380v on it?

If I can trust the schematic, the circuit is not setup as typical power supply circuit used in most TV, in this case the BK-ON is used to turn on Q110 to supply the switched VCC to run the PFC when BK-O is present instead of using PS-ON to turn on the PFC and the rest of other SMPS circuit like typical TV power supply.. So in this case, BK-ON has to be present to supply the switched PFC_VCC for the PFC to run.
The P-ON for this unit is used for turning on (Q203) the switched 12V, and that switched 12V is then used for turning on (Q208) the switched 5V.

[dick_barton]

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.

Q110 Collector should be 13V not Emitter. I would check ZD101 which is a 17.9V zener and the voltage on pin 3 and 4 of U201

[R_J]

Re: Westinghouse EW50T5KW no backlight

It looks like the PON is used to turn on the backlight ic. PON turns on Q116 which turns on Q112 which supplies +5 to U5 VDD

R135 never has voltage across it, so it's never trying to power T103

Check the voltage ON this resistor using EC101 (-) as your meter negative, this is hot ground. Don't measure ACROSS the resistor

[budm]

Re: Westinghouse EW50T5KW no backlight

it looks like the pon is used to turn on the backlight ic. Pon turns on q116 which turns on q112 which supplies +5 to u5 vdd

+1

BTW, the schematic looks be made by some one that reverse engineering it. No Company name, No revision number, No Drawn by, etc.

[speter]

Re: Westinghouse EW50T5KW no backlight

Q110 Collector should be 13V not Emitter.

Correct, my mistake, it's been a while, and a long day.
ZD101 has .5v with just PSon jumpered and between 1 and 8v cycling with BKon jumpered
R135 has 250-350 on both ends, the same readings with BKon jumpered and 161(both ends) when not jumpered
3 and 4 of U201 9.8v with BKon not jumpered between 0 and about 3v cycling with it jumpered
U5 does get 5v with PS jumpered only

[R_J]

Re: Westinghouse EW50T5KW no backlight

You could have a bad (open) EC107, or maybe a shorted ZD102? The Vcc on EC107 should be around 25~30vdc

[speter]

Re: Westinghouse EW50T5KW no backlight

ZD102 checks good, The caps are good, as they hold voltage for a long time after the power is disconnected from the board (minutes). Likely the reason for the low voltage is that B+ is half of what it is supposed to be, the boost is not working (L101)
Where does FB pin 4 of u206 go, and what would be the expected voltage? Pin 2 of u101?

Edit:
Guessing here that from the datasheet that it should be 3.9v or less, and the demo circuit is similar to the ps schematic if FB goes to pin 4

[dick_barton]

Re: Westinghouse EW50T5KW no backlight

Have you swapped out U102. You say you have a steady 5V and 12V with ON/BK not jumpered to 5V but when it is the 5V and 12V pulse approx 40%.
This occurs when PFC_Vcc is activated by BK/ON being jumpered so I wonder if you have a faulty U102

[speter]

Re: Westinghouse EW50T5KW no backlight

I have not tried that yet, as I have no parts like that on hand, i am going check the FB pin on 101, then lift R155, and see what happens.
I haven't had my coffee yet...

[speter]

Re: Westinghouse EW50T5KW no backlight

without BKon jumpered U101 Fb pin is 1.1v, Vcc is 13v, and u102 Vcc is 0.
lifting R151 with BKon jumpered, or not, made no difference.
lifted the gate of Q103, with BKon jumpered supply no longer surges, B+ stays at
160v, Ec104 has 10.5v across it, which is VCC of U102

[R_J]

Re: Westinghouse EW50T5KW no backlight

The Vcc is too low

[speter]

Re: Westinghouse EW50T5KW no backlight

I understand it is too low, because there seems to be trouble when the boost circuit is activated. Because the boost isn't activated until BKon is jumpered(or when the TV boots up) I have to isolate the problem to the boost circuit, or something that starts when the boost voltage is correct.
So if I reconnect Q103, and lift R137 it should show if it is boost, or a problem with T101, But I think it may already be working, because that is where standby comes from?
Maybe I'll wait on lifting R237...
I just thought of something, If T101 is the source of 5v standby, then I should have voltage on Ec 201 205 and 206

[R_J]

Re: Westinghouse EW50T5KW no backlight

I just thought of something, If T101 is the source of 5v standby, then I should have voltage on Ec 201 205 and 206

In your first post you said you had +5 and +12 volts?

I have 5V & 12V with the LED connectors unplugged and BKon jumpered to 5v

That is correct, so if something is shorted (ie: D203) in the +12v circuit, this will also lower the Vcc which is supplied by the same transformer

[speter]

Re: Westinghouse EW50T5KW no backlight

Currently(Q103 disconnected) I have 12 and 5v with Bkon jumpered or not, but with Q103 connected and Bkon jumpered, the voltage on 12 and 5v will cycle between a couple of volts, and their proper voltage, with bkon not jumpered and Q103 connected the voltages are normal.
Is T101 the source of standby voltage?(I think it is), and if that is true I should have some voltage on 201 205 and 206, but I never have voltage on those caps. I have to check that out.

[R_J]

Re: Westinghouse EW50T5KW no backlight

YES T101 is the source for the +5 volts standby. If you have +5v on EC209 and NO VOLTAGE on EC201, Either the transformer has a bad connection on pins 6&7, the winding is open or D203 is shorted, or there is a short on the +`12 volt line somewhere.

[speter]

Re: Westinghouse EW50T5KW no backlight

aargh, I need more coffee or something,I'm making mistakes. I've been staring at this for a couple of days, I like a puzzle, but this is frustrating... EC201,205 and 206 have power
I looked quickly at T101 and thought it was T104 and the caps that have no voltage are actually Ec202,203, and 204.
I tried lifting the gate on Q108,(not shorted) PS still surges with BKon jumpered... so I'm back to the boost circuit somehow?

[dick_barton]

Re: Westinghouse EW50T5KW no backlight

With Q103 disconnected what was the PFC_Vcc voltage?

[speter]

Re: Westinghouse EW50T5KW no backlight

10.5v BKon jumpered
rechecked diodes D102,103,and 104, all good

[dick_barton]

Re: Westinghouse EW50T5KW no backlight

Is this with Q103 still disconnected. With BKon not jumpered PFC_Vcc was 13V earlier?