LF501EM5F No Power, Chirping/Beeping Transformer

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

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

[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.

[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

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 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.

[martystv]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

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

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Normal will be 2~3V range, so you do have LED problem same as the OP in the other thread.

[shadetreetrader11]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I'm having a heck of a time figuring out what to jump where to get the back light on.

[shadetreetrader11]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Well that was a waist of time and resources!!!! Couldn't see this one until the back light came on. My Protect3 voltage was .87 also.
Thanks again budm

[stj]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

smashed screen wont effect the protection circuit.

so you have a smashed screen, bad mainboard and bad led's?
sounds like an un-natural combination - did someone sell you that tv?????

if you fix or bodge the led issue to get the tv running, and verify it sort-of works,
you can sell the boards.
if you take out the led strips you can sell the working ones.

or you can scrap the mainboard and glass, mod the psu to keep the leds on and use it as a workshop lamp.

[shadetreetrader11]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Ha Ya what a deal. I have a friend that picked it up from the curb and asked me if I could get it running for him. And of coarse you always dream of the easy bad cap issues, But that never seems to be the case for me. Ha Ha. So I told him I would take it to the shack and look at it. I'm thinking the main board went bad first with a shorted ceramic cap on the 3.3 vdc voltage regulator circut, and then it made it to the curb and in the process I think it was dropped or damaged or who knows. So that the deal. Thanks for asking.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Well, at least we learn something about this version of the power supply and main board, the 3.3VDC standby Voltage is generated by the main board which gets the 8V from the power supply during the standby mode.

[martystv]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

thanks for your help budm!! I will open the screen this weekend and check out the led's.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

LED tester or good variable power supply with current limitter would have help without taking the panel apart.
I.E.
http://www.shopjimmy.com/sid-gj2c-le...ght-tester.htm

[martystv]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I didn't know they had that. Looks pretty cool. I did take the panel apart and all led's are working.

[citywidetvtech]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

C3214 is shorted on these main boards its underneath L3201 above the black ribbon connector. It took me 5 hours and a hot air gun but finally cleared the short from P-ON+21V to ground. Hopefully nobody else has to go through that, I can still hear the diode check beep in my sleep. Sets will power on now, I haven't found a replacement yet but will keep you posted.

Put small like sized cap from part graveyard in place of C3214 and is working perfect again.

[citywidetvtech]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

C3214 is a 270 Pico cap btw.

[CornerCreekTech]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

@CityWideTVTech! Iam working on the same tv you mentioned with the c3214 cap! I've replaced the cap from another model with the same main board and still getting the little chirp when plugged in! I even removed the cap and just jumped the two points! What am I missing/doing wrong? BTW Iam new to TV repair!

[SLK001]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I even removed the cap and just jumped the two points! What am I missing/doing wrong? BTW Iam new to TV repair!

Sounds like you're new to electronics, too. You NEVER jumper a capacitor. Look at your schematic and see what you probably destroyed.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

@CityWideTVTech! Iam working on the same tv you mentioned with the c3214 cap! I've replaced the cap from another model with the same main board and still getting the little chirp when plugged in! I even removed the cap and just jumped the two points! What am I missing/doing wrong? BTW Iam new to TV repair!

So you jumps the two legs of the filter cap together? if so you may have caused more damages to the circuits.
Did you check to see if the cap shows low resistance before you replace the cap? May be the shorts is not in that power supply section. you need to check the resistance of all the Voltage output pins and GND to see if any one of them show very low resistance when all the boards are connected to gether.