LG 79UB9800 heat problem

[sushi1]

Hello,

My TV is generating excessive amount of heat from the back (especially around the main board and psu areas) even after operating for just a few minutes.
I recently switched the main board due to video problems (maybe from the heat??) and I am really worried the new main board might eventually get the same problems.
tried connecting it to a surge protector as well as directly to the wall, nothing helps.

The TV supports 100-240v, and I run it on 220v.
Shall I try connecting it to some sort of a stabilizer that outputs 110v?

if that’s not the case, what could it be?
I am sure this heat shouldn’t be normal.

Model: LG 79UB9800

thanks.

[heavymachines]

Re: LG 79UB9800 heat problem

If the t.v is working good, i assume it is since you replaced main. You may need to modify it with fans. However is this tv running in air conditioned environment? Or is it room temps which i assume your area is rather warm.

[sushi1]

Re: LG 79UB9800 heat problem

the tv is working great and I always make sure the room temp is good, plus there’s an AC right above the TV, but AC or not, it still gets considerably hot, so I don’t really think installing fans would help much.

I was wondering if voltages can do that?
and whether lowering the input voltage (within supported range) would help.

[heavymachines]

Re: LG 79UB9800 heat problem

Is your a/c unit sharing same outlet or plug as A/C unit or same breaker at fusebox? if so then that explains it perfectly why your tv is running hot. Heavy draw on same circuit can cause everything plugged into it run hot.

[sushi1]

Re: LG 79UB9800 heat problem

Just checked and nope they’re on seperate breakers and plugs.

[heavymachines]

Re: LG 79UB9800 heat problem

Fan mod is only solution i can think of , others might chime in with other ideas.

[vinceroger69]

Re: LG 79UB9800 heat problem

doing a fan mod does sound a good solution may have to cut back tv casing to allow good air flow and mount a fan or two over the main bga ics

[sushi1]

Re: LG 79UB9800 heat problem

the worst TV i’ve ever dealt with, so frustrating not being able to figure it out... no more LG products for me.

[Hamie]

Re: LG 79UB9800 heat problem

LG really are making the worst mainboards ever.
I used to think they were bad but recently they have taken it to a whole new level of shit.

[sushi1]

Re: LG 79UB9800 heat problem

yeah don’t know whether it’s a mainboard fault, psu or poor ventilation and design, What I do know for sure is that LG is trash.

[Davi.p]

Re: LG 79UB9800 heat problem

Suppling it with 110vac doesn't make any difference i think, you have to remove the back cover, and locate more precisely the heat, don't touch directly anything on the psu even with mains disconnected, use something flat and very hard to touch but not metal, it has to be thin, like a piece of glass, let it to warmup and check the part that is warming too much. A possible reason of it can be bad capacitors > high ripple, if you can replace them with good brands. Another possible reason is bad soldering on both mainb. / psu.

[sushi1]

Re: LG 79UB9800 heat problem

Not willing to take it off again, plus I am not much a tech. to check for bad caps and soldering stuff..
I have another thread and you suggested switching the mainboard, it worked and I thank you for that. In the mean time i’ll just hope it doesn’t go bad.

If you visited Egypt, come and take a look at it yourself (kidding)

[Davi.p]

Re: LG 79UB9800 heat problem

My suggestion is not strictly for your operation, you can let to make it by a tech. If any tech there is not able to change caps you're put wrong..

[sushi1]

Re: LG 79UB9800 heat problem

Will see what I can do, will definitely bring a tech soon.
Last question:
I can also feel static electricity running though the TV metal frame when I touch it even if it’s unplugged and nowhere near other devices, it’s on a wooden cabinet.
does this indicate voltage leak or is it normal?

[heavymachines]

Re: LG 79UB9800 heat problem

Interesting. With it plugged in one would think it is lacking ground at the outlet can cause metal chassis to give you a shock. As with anything lacking ground plugged into outlet.


Or the air is really really dry can cause static.

Or you have something wrong in circuitry energizing the chassis. Current leakage to chassis can be a pin on backside touching metal or cap etc.


Dunno let other chime their opinions.

[sushi1]

Re: LG 79UB9800 heat problem

well it has been unplugged for nearly 30 mins now and can still feel the static, and nothing is touching it or plugged in it.

[heavymachines]

Re: LG 79UB9800 heat problem

Weird. Only thing i can think of is a capacitor storing energy and leaking to chassis. I am certain when a circuit is working correctly the built in resistors will drain them after it is unplugged unless there is something wrong. such as it touching chassis somewhere bypassing the resistor or something failed in circuit and energizing the chassis.


I think i have read something similar somewhere on bad caps forums. Let the more experienced folks chime in on this one.

[Davi.p]

Re: LG 79UB9800 heat problem

One thing is static electricity, one is leakage to ground currents, the first charges the metal chassis with a certain amount of charge that when you touch it you discharge it, the second is flowing continously and you feel it every touch, there can be a possible leakage on the big condensers i think, one more reason to change'em all even the 450v ones if needed. Not all PSU have discharge resistors so you can have charge after hours of wall plug unplugging.

[sushi1]

Re: LG 79UB9800 heat problem

Should I be concerned? let the tech change the condenser? anyways I've attached the power supply pic. , if it doesn't have resistors or maybe anything odd that can be seen (I know that's unlikely).

[Davi.p]

Re: LG 79UB9800 heat problem

The 450v capacitors can't be because them are not connected to ground, the cap before the bridge are low capacity, them aren't, to feel a current with the hand the metal must be at high potential, i think more than 40v, so only the 100v cap for the backlight can be, but them can discharge to the leds probably, so i think the voltage come from antenna or if is not connected i don't know... need schematic..