LF501EM5F No Power, Chirping/Beeping Transformer

[shadetreetrader11]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Budm how about we start right where pillit83 quit. I have 168vdc

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I have same tv with same exact problem and I'm wondering the same

sch shows 230V.
See this thread for the schematics.
https://www.badcaps.net/forum/showth...ight=LF501EM5F

[shadetreetrader11]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I have same tv with same exact problem and I'm wondering the same

[jeffer76]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

I have the same exact problem. Same voltages and symptoms.
Was wondering if anyone was able to solve this problem? Main or Power Supply?

[stj]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

well i'm in a country with REAL mains voltages!
but if you scan the tv section of the forum you can find what the pfc voltage should be for the u.s.
i'm sure it should be higher than that.

[pillit83]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

i get 161vdc with the negative lead of my DMM on the negative terminal of the big cap and the positive lead on the jumper marked "PFC_VOUT".

[stj]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

well the psu looks wrong, but dont rule out a fault on both.

so lets start with the psu.
what are you getting on pfc-vout?
it should be a few hundred i imagine.

[pillit83]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Going off the labels you pointed out, I have:

(power supply plugged in, nothing connected to it)
amp +13v -> reads 8.18vdc
p-on +21v -> reads 13.53vdc
p-on_H2 -> reads 0.00vdc
all +3.3v -> reads 0.00vdc
bl-sw -> reads 0.00vdc

(power supply plugged in, main board connected to it, transformer beeping)
amp +13v -> fluctuating 3.8vdc~4.1vdc
p-on +21v -> fluctuating 0.00~1.2vdc between beeps
p-on_H2 -> reads 0.00
all +3.3v -> fluctuating 0.00-0.8vdc between beeps
bl-sw -> reads 0.00

Does the fact that all the voltages are low even before the main board is plugged in indicate that a problem is likely on the power supply board?

[stj]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

btw, it's probably a shorted ceramic cap on the main board.
i'v had that few times on LG
a bastard to find btw!

[pillit83]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Oh wow you're right. I hadn't noticed the labels before but now they jump out at me. A 2nd pair of eyes on a problem is invaluable! Thanks! I'll do some prodding and report back

[stj]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

if you look at the screenprint under the psu, it's all marked.

i see:
gnd
amp +13v
p-on +12v
p-on H2 <???
all +3.3v

near the invertor is bl-sw

in the center is PFC-Vout

for a piece of shit it's pretty well labelled.

[ReeceyBurger123]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Whatever... I am sure that there is a short somewhere on the output side of the transformer and oops for some reason there is!

Ok in this case yes, but what im saying is that I have seen power boards where there is a short make a whine noise and in some cases make a tick noise, it works both ways. I dont see why you are getting that way I was merely pointing out what you were saying is not 100% true mate.

[CapLeaker]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Thats not always the case Capleaker youtube use Maxarcade has a video of repairing a set based off a similar chassis and his had a shorted diode and it made a whining noise so what you are saying is slightly correct but not 100%.

Whatever... I am sure that there is a short somewhere on the output side of the transformer and oops for some reason there is!

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

So it is either the main board is drawing too much current and cause it to go into startup/shut down mode or the power supply is false and cannot handle the load.
More In depth trouble shooting required, you will have to start checking the load resistance of the power supply outputs to see if any one of them show very low resistance.
You will need to look at the bottom side where the connector CN501 is to see which one are the power pins.
"As soon as it's plugged in (to mains) it starts to "chirp" at around 2 second intervals repeatedly and will not power on. " so it is doing it in standby mode.

Pictures provided by SHOPJIMMY.

[pillit83]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

It stops ticking when the cable is removed. Starts ticking again when the cable is reinserted.

[budm]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

The Bottom right transformer is the power supply for the main board, what happen if you remove the flat white ribbon cable, will it is still ticking?

http://www.shopjimmy.com/emerson-a3a...upply-unit.htm

http://www.shopjimmy.com/emerson-lf5...repair-kit.htm

http://www.shopjimmy.com/catalogsear...rson+LF501EM5F

I have no idea how much time you will want to spend on component level repair.

[ReeceyBurger123]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Thats not always the case Capleaker youtube use Maxarcade has a video of repairing a set based off a similar chassis and his had a shorted diode and it made a whining noise so what you are saying is slightly correct but not 100%.

[CapLeaker]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Usually a tick tick tick in a transformer means that there is a short on the output side off it. Most of the time it is a diode, but also could be a shorted cap or something else causing a short. That is why the input circuit of the transformer tries to start, but it gets shut down again. Hence the tick tick tick.

[ReeceyBurger123]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

Ok now that you have tested the diodes you need to check the primary fets and there respective resistors.

[pillit83]

Re: LF501EM5F No Power, Chirping/Beeping Transformer

yes of course, I tested all of them. I noticed the SMD diodes that are situated near multiple resistors tested bad in circuit but after removing them i see they're good