LG 37LC7D no indicator light

[ckwplve]

Hi everyone,

I'm new to this whole repair thing, so please bear with me. I'm an EE student right now, trying to get some more practical hands-on skills. Hopefully I'll learn something and get a functional TV out of this process!

So, I have a non-functional LG 37LC7D right now. It came out of a friend's father's garage - "If you can fix it, you can have it" he said, so I thought I'd try my hand at repairing it. Unfortunately, he doesn't remember anything noteworthy about what happened when the TV quit working.

I tried following budm's guide, but unfortunately it's written a little too tersely for someone with as little knowledge as me.
https://www.badcaps.net/forum/showpo...56&postcount=1


Anyway, the main symptoms are that when I plug in the TV, the red indicator light doesn't come on. When I try switching on the TV by pressing the power button on the side of the TV, or on the remote, nothing happens. No typical high-frequency noises, no audio, no display.

So naturally, I cracked open the TV to look for any glaring issues. I didn't see anything obvious, no bulging leaky caps, no burned up ICs or resistors or anything. I checked the 2 fuses with a multimeter and neither are blown. I also checked the main power line coming from the wall to the board, and we have 120vac at that connector when plugged in.

This is where I'm stuck. I feel like the fact that there's no indicator light means that there must be a power issue somewhere - I just don't know where to start looking. I checked that the board is getting power, but now I don't know how to follow along through the various components without a schematic, to know what parts are supposed to receive what voltages during normal operation. Can someone point me in the right direction?

Also, is there some kind of common annotation I should know that signifies which sections of the board are "hot", and which sections have already been rectified to small DC voltages? I feel like that would be helpful too, in the interest of safety...

I attached images of what I believe to be the power board (front and back). Perhaps if someone is familiar with the board, then you could lend me a few pointers?

Thanks in advance for the help. I appreciate any advice you can share. Let me know if there's any additional info or pictures I should provide that would be useful.

[saddle_au]

Re: LG 37LC7D no indicator light

Just fixed a LG 32LC7D yesterday with same power supply and same fault, no standby light.

First, don't ignore the caps issue. They are notoriously bad in this power supply. I have included an image with all of the caps you should replace or change to make more reliable long term. This is the standard set to change on this power supply and can be purchased as a kit from ebay. The full kit is supposed to be for the board when it goes into the 37 inch tv (and the p/s has been built with two main filter caps not one). Odd your 37 inch has the P/S with the reduced cap number and values.

The TV I had would not power up even though the standby was present, the standby light was not on and it just sat there dead as a doornail. Well, mine turned out to be the cabling between the main board and the power supply. You could wriggle the two power connection cables near the motherboard and the standby light would come and go. You could get the tv to start by holding the cables a certain way, but if you released them it'd immediately shutdown. The killer was the third wire in on the larger cable bundle.

The crimps in the cables were no good. I cleaned the connectors at both ends and individually pulled out the crimp females (on the cables) carefully, one at a time, squeezed the rear end of the crimp shut a bit and put it back in, then do the next one. To remove a crimp from the plastic holder you need to flatten the clip flange on the crimp so it can be pulled out of the slot (see image attached). Mod the crimp shape, raise the flange again and reinsert. I could have just put new crimps on, but I wasn't sure if I had that style or size and this was just as quick.

TV has run 24 hrs now ok. Hope this helps.

[ckwplve]

Re: LG 37LC7D no indicator light

Oh wow, thanks saddle_au for the fast reply!
I'll look into getting replacement caps and soldering them in.
What cable are you talking about, specifically? Is it the bundle of cables that plugs in to the connector that's visible in the top left corner of your attached photo? (Or at least, one of those two bundles?)

[stj]

Re: LG 37LC7D no indicator light

we dont recomend caps from ebay here - you dont know what crap they may be using.

your in the u.s. so make a list of all the caps and go look at panasonic FR series from digikey.
when you make a cap list you need the capacitance, the voltage AND the diameter & height.

[stj]

Re: LG 37LC7D no indicator light

btw, that highlighted connector looks like JST VH series.

[saddle_au]

Re: LG 37LC7D no indicator light

Totally agree about the caps, sorry I was not clear about this. Only use the ebay listing to get the number and types to buy.

I used the ebay listings to get the values needed as someone had plonked in whatever ones they had in the board during a previous repair attempt. I didn't have a schematic and I was not sure of the value of the 1500uf 35v one in the middle as when I got it, it was a 1000uf 50v which really didn't seem right to me. The kits use a lot of 2200uf and 470uf caps with one 1500uf 35v. Replace the lot with Panasonic caps as suggested above, get them from digikey, get them here on the bad caps site. I just live in a geological oddity (3 weeks from anywhere is the standard answer ordering stuff). Try and get thin tall ones instead of short fat ones to make replacement and fitting easy. There's a good clearance to the case above.
https://www.badcaps.net/pages.php?vid=22

The two individual strand cable sets between the power supply (that plug into the two connectors in the image I set back) and the motherboard should be checked for consistency in connection. They are/were terrible in the unit I have due to age/corrosion. To get a call for help for the same unit with the same 'death' mode on the same day as a fix occurred, just surprised me as well. Yours may not be the same fault of course, but whats the chance it is (same age, same unit, same symptom).

I also used a bit of cleaner on the pins themselves. I normally would have swapped the clips out, but as I said before, I wasn't sure of the style, it was late and the radio was running a funny show so 25 minutes of pull, reshape, refit, pull, reshape, refit.... was just as quick.

When it is all running, use some rubber/silicon compound to tie the cap tops together to minimise individual movement. Try not to use it a pcb board level, sometimes this stuff goes conductive after a while.

Good luck.

[lookimback]

Re: LG 37LC7D no indicator light

[QUOTE=saddle_au;571782
The crimps in the cables were no good. I cleaned the connectors at both ends and individually pulled out the crimp females (on the cables) carefully, one at a time, squeezed the rear end of the crimp shut a bit and put it back in, then do the next one.
[/QUOTE]

I prefer to flux and solder them when the crimps are loose.