LG 37LE500 lcd blinking

[alberich2k5]

Hi everyone

I am trying to repair my former TV, an LG 37LE5500, mainly for learning purposes.
The issue is: when I turn the TV on it starts blinking and rebooting, repeating this cycle for about 10-30secs. After that, it works correctly with no issues.

I started by looking at the power supply (EAY60803001; attached front and back pictures provided by shopjimmy) measuring the following lines (bunch of cables going to main board):


PIN *******StandBy PWR ON
-------------------------------------------------------
ERR-OUT 2.864 2.838
P-DIM 0.252 1.202
N.C. *******- -
DRV-ON 0.061 1.932
N.C. *******- -
GND ***** - -
3.5V *******3.49 3.455
3.5V *******3.49 3.455
GND *******- -
GND *** - -
20V *******0 18.43
20V *******0 18.43
N.C. * -
12V ******0 12.07
12V ******0 12.07
12V ******0 12.07
GND ***** - -
GND ***** - -
3.5V *******3.49 3.455
3.5V *******3.49 3.455
GND ***** - -
GND ***** - -
20V *******0 18.43
PWR-ON 0 3.323

I found that 20V and 3.5V lines differ about 10% from what they should be reading when TV is on. Note when in stand by 3.5V *line are pretty accurate, 3.49.

So I decided to trace the 20V back, checking for bad components; I reached *to the area from the attached picture (closer look, with numbers). Here, if I read in-circuit resistors values and obtaining completely different values then they should be for most of them.

Values are:
1. resistor code 203 **-> reading 18.35K
2. resistor code 4701 -> reading 3.784K
3. resistor code 203 *-> reading 4.80K
4. resistor code 102 *-> reading 962 ohms
5. resistor code 2203 *-> reading 22.63K
6. resistor code 105 *-> reading 8.89K
7. Cap not shorted (don't know if its good or not)
8. resistor code 272 *-> reading 4.68K
9. resistor code 153 *-> reading 15.06K

I have other SMD resistors spread around the power supply board: for example 105 which are reading 0.85Mohms a couple more 202 reading 1.5K

Is this way of reading smd resistors fine? If yes, does this mean I have all these resistors failing? aren't they so many?

Thanks in advance

[alberich2k5]

Re: LG 37LE500 lcd blinking

Sorry to insist on this one, but I really want to learn the process of troubleshooting electronics (at least the basic level)

Thanks once again

[budm]

Re: LG 37LE500 lcd blinking

When it is working correctl , are those Voltage readings still the SAME?

[alberich2k5]

Re: LG 37LE500 lcd blinking

When it is working correctl , are those Voltage readings still the SAME?

Thank you budm for replying
Yes, they are the same.
3.5v are slightly different: once it is working correctly readings are 3.465v

How about the sms resistor I was asking about? Is it correct what I was doing?

thanks

[budm]

Re: LG 37LE500 lcd blinking

You cannot get accurate resistance reading of the resistor when measured in the circuit.
Rebooting cycling is more likely there is problem on the main board during startup.

[alberich2k5]

Re: LG 37LE500 lcd blinking

So better I should start looking at main board?
I have no clue were to start on any starting suggestions?

About the 20V line on the power supply, should stop looking at it (is it ok the 18.4v)? or just postpone it?

Thank you very much for your time and patience

[moateez]

Re: LG 37LE500 lcd blinking

Try to rehot schemic capasitor on power splay and turn on your tv

[alberich2k5]

Re: LG 37LE500 lcd blinking

Try to rehot schemic capasitor on power splay and turn on your tv

which one is that? (I googled before asking you)

[moateez]

Re: LG 37LE500 lcd blinking

Sir rehot all capasitor in secondary of power splay in rehot is better to youse hot gun

[alberich2k5]

Re: LG 37LE500 lcd blinking

Sir rehot all capasitor in secondary of power splay in rehot is better to youse hot gun

I am really sorry but I couldn't understand what your mean
Where are the capacitors in secondary of power suply? Most power supply capacitors are DIP sized, you mean reflow all of them?

[angelos]

Re: LG 37LE500 lcd blinking

No he says you should heat them up on the power supply using a paint stripper gun without melting everything. Get those caps to a cozy 50 degrees celsius and then plug in the tv and see if the rebooting occurs.
I would rather used the heat gun on the main board focusing on the caps there since i have had it in the past that some caps "dry out" and heating them makes them work a little better thus proving a point.

So, heat up the power supply and start TV and observe power cycling.
Secondly do the same to the main board and see results.

[moateez]

Re: LG 37LE500 lcd blinking

No he says you should heat them up on the power supply using a paint stripper gun without melting everything. Get those caps to a cozy 50 degrees celsius and then plug in the tv and see if the rebooting occurs.
I would rather used the heat gun on the main board focusing on the caps there since i have had it in the past that some caps "dry out" and heating them makes them work a little better thus proving a point.

So, heat up the power supply and start TV and observe power cycling.
Secondly do the same to the main board and see results.

+1 this is what i mean soryy for my english

[alberich2k5]

Re: LG 37LE500 lcd blinking

@moateez no worries at all, and thank you so much for your time

I did the heating experiment:
Power supply board - still blinking, but no reboot
Main board - still blinking, but no reboots

However, once the main board cooled down rebooting issues came back.
I re-heat it again, et voila, reboot issues gone (but still blinking)

And after few seconds TV was turned on, blinking was gone.

So I guess they are two separete issues?

[moateez]

Re: LG 37LE500 lcd blinking

but fisrt you shlou heat just power suplly not motherboard to find easly the probleme


*** if after heating power th not worck you go to heat motherboard

now try to change all capasitor like this Red Points

[alberich2k5]

Re: LG 37LE500 lcd blinking

Sorry, I miss explained myself

First I heated the powersupply and turned on the TV, the rebooting was gone but not the blinking.
Later I did the same with the main board, with the same results.

However, once mainboard cooled down, the rebooting issues came back. So i re-heated the main board and they were gone.

Before starting this post I replaced the 6 caps you marked me since the readings for 12V lines were about 11.5V. (That solved that issue for 12V lines but it didn't for 20V and 3.5V lines)

[angelos]

Re: LG 37LE500 lcd blinking

You should replace all the caps on the main board if you don't have a ESR meter since this TV is quite a few years old and the capacitors have reached their end of life cycle. The internal resistance of the capacitors has gone up due to the drying of the electrolyte within them. So even if the capacitance measure within 10% of its rated value you might measure the ESR value to be elevated considerably. Caps are cheap, Just replace with care since you have to apply a lot of heat on the ,main board in order to melt the solder. Don't damage any tracks by lifting the cap prematurely.

[alberich2k5]

Re: LG 37LE500 lcd blinking

Will do that angelos, and let you know guys. I need to order the caps, and it is going to take a while. I will let you know as soon as I replace them all.

Meanwhile I'm thinking about buying an ESR meter. Any decent - affordable one you can recommend me?

[vinceroger69]

Re: LG 37LE500 lcd blinking

These esr meters are good value for the money and can update the firmware too
https://www.aliexpress.com/item/2016...08.0.56.J7yA7x

when you have the tv working after heating the mainboard does the led stop blinking on the front of the tv some lgs do take a while too stop blinking ive noticed

[alberich2k5]

Re: LG 37LE500 lcd blinking

when you have the tv working after heating the mainboard does the led stop blinking on the front of the tv some lgs do take a while too stop blinking ive noticed

vinceroger69, ordered thank you very much

Front led works as usual, I haven't notived any thing different.
I also ordered the caps for the main board, will see if I can get it to work; it is quite exciting hehehe

[vinceroger69]

Re: LG 37LE500 lcd blinking

can you post a picture of the mainboard used in this set thanks
This forum has all the firmware and mods for that tester its a long read but worth it
https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/