switch mode power supply no power, have diagram

[football0062]

tv is a lt-40fn97 full of boards, main board sub board, just tons. issue it it comes on but no picture or sound. but ive noticed the sub power board assembly has no output and the waveform for the transformer looks kinda crazy. can anyone look at this diagram and see what switches this power supply on? or if its always one when the AC line in connected. the AC line does come off a relay on the main pwb, but its working fine. i hooked it up straight to the wall and still nothing. ill attach the diagram for sub pwb,and the waveform im getting on primary side. bit funky.

[budm]

Re: switch mode power supply no power, have diagram

This power supply may be switched on (gets the voltage at CN900D) when the main board gets the power on signal from the power switch or from the remote.
What DC voltage do you have on C9001, measured right at the two legs of the cap?
Pictures of the rest of the board and SCH?

[football0062]

Re: switch mode power supply no power, have diagram

This power supply may be switched on (gets the voltage at CN900D) when the main board gets the power on signal from the power switch or from the remote.
What DC voltage do you have on C9001, measured right at the two legs of the cap?
Pictures of the rest of the board and SCH?

CN900D is the AC input from main power board, it runs 120VAC not sure why the manual has it at 375VAC. anyway bridge is good, C9001 is running about 170VDC. no shorts that i can find, just can get a feedback from my opto obviously. i was looking at that Ic you put the datasheet on and its not running that typical application where would you suggest i go from here?

[football0062]

Re: switch mode power supply no power, have diagram

This power supply may be switched on (gets the voltage at CN900D) when the main board gets the power on signal from the power switch or from the remote.
What DC voltage do you have on C9001, measured right at the two legs of the cap?
Pictures of the rest of the board and SCH?

heres the full service manual had to break it into 2 parts or it wouldnt upload.

[football0062]

Re: switch mode power supply no power, have diagram

heres the full service manual had to break it into 2 parts or it wouldnt upload.

wont let me upload 2nd part, just board layouts anyways though. think i went over the file size limit

[football0062]

Re: switch mode power supply no power, have diagram

heres pics of the board

[budm]

Re: switch mode power supply no power, have diagram

OK, you will be using the negative leg of C9001 as the Ground ref. point for measuring the voltages on the Primary (HOT) side.
Check the dc Voltage on VCC pin4
Check Source resistor R9002.
Check Zener Diode D9001
Check Caps C9010, 9011

[football0062]

Re: switch mode power supply no power, have diagram

OK, you will be using the negative leg of C9001 as the Ground ref. point for measuring the voltages on the Primary (HOT) side.
Check the dc Voltage on VCC pin4
Check Source resistor R9002.
Check Zener Diode D9001
Check Caps C9010, 9011

thats what i was following this morning, was the VCC its only 3.7V traced it back to source from D9022 to R9004 then through the opto.

heres voltages.
R9002 0V
c9010 2.7V
c9011 3.7V
ZD9001 3.7V

also getting a 55V drop across R9004

[budm]

Re: switch mode power supply no power, have diagram

ZD9001 is 33V Zener, R9004 is feeding the startup voltage to the VCC pin, once the IC starts driving the transformer, the VCC will be fed by the aux winding of the transformer through the rectifier D9004. So it may have bad Zener diode, or internal low resistance on the VCC pin, bad C9011. You also should check the value of that filter cap 9011. Check the value of R9004 also, it is fed by the half-wave rectifier diode to supply the start-up voltage.
The IC running voltage is 18.2V typ., stop voltage is < 9.7V. Right now it only has about 3VDC.

[football0062]

Re: switch mode power supply no power, have diagram

ZD9001 is 33V Zener, R9004 is feeding the startup voltage to the VCC pin, once the IC starts driving the transformer, the VCC will be fed by the aux winding of the transformer through the rectifier D9004. So it may have bad Zener diode, or internal low resistance on the VCC pin, bad C9011. You also should check the value of that filter cap 9011. Check the value of R9004 also, it is fed by the half-wave rectifier diode to supply the start-up voltage.
The IC running voltage is 18.2V typ., stop voltage is < 9.7V. Right now it only has about 3VDC.

thanks for the reply, making alot more sense now, but still cant quite get it, heres what ive done.

Replaced the 33v zener
replaced R9004. its 47k 2W, i lowered it to about 25k and voltage goes up to about 7VDC
replaced the half rectifier diode d9022
replaced C9011.

nothing changed still stuck with the 3.7VDC on pin 4. guess it could be the IC, any way to check it? also should i try replaceding D9004 before going after the IC?

[budm]

Re: switch mode power supply no power, have diagram

You can check the resistance between the VCC pin and the ground pin, something is loading down that VCC line some how.

[football0062]

Re: switch mode power supply no power, have diagram

You can check the resistance between the VCC pin and the ground pin, something is loading down that VCC line some how.

yup thats it, 4kohm VCC to gnd. quick fire up with ic out of circuit and voltage quickly rises. only ran for half sec tho. ordering new IC ill let u know. thank you