LG 42lc7d low standy voltage

**CapLeaker** · 03-08-2015, 07:09 PM

Re: LG 42lc7d low standy voltage

That is one thing that I don't understand, why the PFC would be low like that. Maybe some feedback circuit leaking diode, or a resistor that changed value? The backlight circuit only works when the PFC is working correctly. 340V is the lowest I've ever seen.

**budm** · 03-08-2015, 07:21 PM

Re: LG 42lc7d low standy voltage

Originally posted by CapLeaker

That is one thing that I don't understand, why the PFC would be low like that. Maybe some feedback circuit leaking diode, or a resistor that changed value? The backlight circuit only works when the PFC is working correctly. 340V is the lowest I've ever seen.

That is what I am thinking too that either feed back is bad or bad filter caps but not likely to have two bad filter caps.
I cannot find any good pictures of the bottom side of the board, SJ does not have one either.
Looks like we will need d good clear picture so we can locate the PFC IC and get the spec sheet for it.

**CapLeaker** · 03-08-2015, 07:24 PM

Re: LG 42lc7d low standy voltage

Can't find a service manual PDFs for it either. If it would be capacitor related, it should be a dead give away on the oscilloscope. I wonder... Any caps running hot?

**topfli8979** · 03-09-2015, 09:20 AM

Re: LG 42lc7d low standy voltage

Inverter fuse is good. As far as hot caps, I dont have a oscilloscope yet, working on that.

**topfli8979** · 03-09-2015, 09:23 AM

Re: LG 42lc7d low standy voltage

Back of power supply, I dont know why its loading horizontal. Left side is top of psupply.

Attached Files

if you find these attachements useful please consider making a small donation to the site

**budm** · 03-09-2015, 09:25 AM

Re: LG 42lc7d low standy voltage

Right now I am suspecting the brown coupling cap right next to the inverter transfomer.

**topfli8979** · 03-09-2015, 09:56 AM

Re: LG 42lc7d low standy voltage

Forgive my ignorance bud, but are you referring to the large transformer on bottom left? I also found some burnt looking dust coming from the bottom of the inverter on the bottom left.

Attached Files

if you find these attachements useful please consider making a small donation to the site

**budm** · 03-09-2015, 10:14 AM

Re: LG 42lc7d low standy voltage

Originally posted by topfli8979

Forgive my ignorance bud, but are you referring to the large transformer on bottom left? I also found some burnt looking dust coming from the bottom of the inverter on the bottom left.

Yes, that is the inverter section.

**budm** · 03-09-2015, 10:16 AM

Re: LG 42lc7d low standy voltage

BTW, can you make in focused pictures of the bottom side, also make it straight shot pictures?

**topfli8979** · 03-09-2015, 10:30 AM

Re: LG 42lc7d low standy voltage

Bottom side inverter transformer

Attached Files

if you find these attachements useful please consider making a small donation to the site

**topfli8979** · 03-09-2015, 10:32 AM

Re: LG 42lc7d low standy voltage

Bottom side above inverter section

Attached Files

if you find these attachements useful please consider making a small donation to the site

**topfli8979** · 03-09-2015, 10:33 AM

Re: LG 42lc7d low standy voltage

Bottom side main board connections

Attached Files

if you find these attachements useful please consider making a small donation to the site

**topfli8979** · 03-09-2015, 10:36 AM

Re: LG 42lc7d low standy voltage

Bottom side main power connection

Attached Files

if you find these attachements useful please consider making a small donation to the site

**topfli8979** · 03-09-2015, 10:53 AM

Re: LG 42lc7d low standy voltage

I also removed the the brown coupling capacitor, measures 40 ohms max out of circuit.

**budm** · 03-09-2015, 11:37 AM

Re: LG 42lc7d low standy voltage

Originally posted by topfli8979

I also removed the the brown coupling capacitor, measures 40 ohms max out of circuit.

Are you testing the resistance or the ESR?
How about the capacitance reading?

**budm** · 03-09-2015, 11:45 AM

Re: LG 42lc7d low standy voltage

U600 should be the PFC Controller IC, we need the P/N to get the spec sheet.

**topfli8979** · 03-09-2015, 01:44 PM

Re: LG 42lc7d low standy voltage

I was testing the resistance with dmm. Capacitance is 1.022 uf.

U600 looks to have been hot, the top is distorted, what i can read is 5501a i beleive

**budm** · 03-09-2015, 01:54 PM

Re: LG 42lc7d low standy voltage

The capacitor should show infinite resistance, if it shows as 40 Ohms using Ohm mode then you do have problem with that cap. Is the printing on the cap is 105XXXX?

**topfli8979** · 03-09-2015, 01:56 PM

Re: LG 42lc7d low standy voltage

M 105J MP
500vt0445

**budm** · 03-09-2015, 02:01 PM

Re: LG 42lc7d low standy voltage

Originally posted by topfli8979

M 105J MP
500vt0445

It is 1uF 5% 500V.
So you should verify the resistance again for sure.

LG 42lc7d low standy voltage

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Comment

Related Topics