LF501EM5F No Power, Chirping/Beeping Transformer

[martystv]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

With the backlight on I'm getting .9v on PROTECT3 jumpers

[martystv]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I think maybe I got a hold of a bad new main board. After getting the leds on found I can't turn the tv off with the on/off button, I don't have any on scree display either.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Once you get the BACKLIGHTS to come on, you will then need to check the PROTECT3 signal.

[martystv]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I read through the posts and first I jumped 3.3v to bl-sw and got no change. When I added a second resistor to bl-adj the led's did light up so a little progress was made.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I have the same set(lf501em5f). It was also chirping and I also changed the main board. I now have the same thing as shadetreetrader11. 47 v at the led plug. I'm not sure yet but I think the problem is with the bl-sw circuit. I have 3 jumpers (j116,106,103) all labled bl-sw but all three have 0v.

Read post 40 and the rest, you will need three resistors to test the backlights circuit.
https://www.badcaps.net/forum/showth...t=54078&page=2
Pay attention to the PROTECT3 signal.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

BL-SW (same as BL-ON) is generated by the Main board.

[martystv]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I have the same set(lf501em5f). It was also chirping and I also changed the main board. I now have the same thing as shadetreetrader11. 47 v at the led plug. I'm not sure yet but I think the problem is with the bl-sw circuit. I have 3 jumpers (j116,106,103) all labled bl-sw but all three have 0v.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

The red LED is on but not sure about the bl on Sig. I know the back light it's self isn't on. And there's 3 wires that each have 47 volts to ground on them that are going to the back light.

So at least now you do have Red LED on, does it change state when you have activate/deactivate the power switch on the remote or on the TV?

[shadetreetrader11]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

The red LED is on but not sure about the bl on Sig. I know the back light it's self isn't on. And there's 3 wires that each have 47 volts to ground on them that are going to the back light.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Per diagram it shows around 230V, so I do not believe that the PFC Boosted Voltage is that high in the 400VDC range.
Since you do have full 13V and full 21V that means the main board is now sending the PS-ON to turn on the power supply to run in full mode.
So do you now have the LED on the front of the TV now since the 3.3V is now present?
Also do you have BL-ON and the dim control signals?

[shadetreetrader11]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Yes you are correct. 218 volts

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Ok Main Board showed up today and I measured 900 ohms from the large tab of the 3.3 volt regulator to ground. (Much better) So I put the board in the tv and it still won't fire up. Here is a list of the voltages I have. They all seem to be present. It just won't produce the 390 volts.
All +3.3 3.3v
Amp 13v 13v
P-on 21 22v

So the power supply is now putting out the correct Voltages now with the new main board which supplies the 3.3V back to the power supply board.
So what DCV do you have on the main filter cap? around 230VDC?

[shadetreetrader11]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Ok Main Board showed up today and I measured 900 ohms from the large tab of the 3.3 volt regulator to ground. (Much better) So I put the board in the tv and it still won't fire up. Here is a list of the voltages I have. They all seem to be present. It just won't produce the 390 volts.
All +3.3 3.3v
Amp 13v 13v
P-on 21 22v

[CapLeaker]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

capLeaker. I took your advice and fed about 1.5 to 2 volts threw it and the main IC got warm. I ordered a main board already. I was really wanting to fix that one but o well. I sure learned a lot and I guess that's the main objective.

Yeah... too bad. Maybe you find a replacement IC on aliexpress or ebay. Tinkering with stuff is fun and learning something new is always exciting. I think you did pretty good. Here are quite some knowledgeable folks on this board.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

When you get the replacement board, make sure to take some resistance readings for the supposedly 'Good working board' just in case.

[shadetreetrader11]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

capLeaker. I took your advice and fed about 1.5 to 2 volts threw it and the main IC got warm. I ordered a main board already. I was really wanting to fix that one but o well. I sure learned a lot and I guess that's the main objective.

[CapLeaker]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Push some power through with a variable power supply. It should get roasty toasty whatever is bad, unless it is heatsinked somehow.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

That reading is with or without the cable between the main and power supply board connected?
There is a small ceramic cap C3608 connected between the tab and GND, those kind of cap tends to fail as shorted circuit.

Did you check that cap by removing it?

[stj]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

more likely a shorted ceramic cap

[shadetreetrader11]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I've tried to trace it back I have shoved tiny wires threw the board (Double sided) and I keep ending up into the main IC 3101 thing has 156 legs. I really need a schematic. My circut level is nothing compared to yours. I'm a little beaten I think. But I did learn a lot from the whole deal. Just had a friend bring over a different tv to look at so maybe I'll move on to that one. Can't say we didn't try. Thanks guys