LG LE37LH4000-ZA Tcon Issue?

[dick_barton]

Picked up this set. The original fault was described as taking 30 – 40 mins for a full picture on the screen from switch on cold. Initially there would be only several horizontal lines across the top of the screen and over time this would build up to form a full picture.

Removed the ribbons to clean the contacts after which I no longer get a picture.

Everything else is working and I can play a DVD through the TV, raise the volume up and down, mute the sound etc.

Pictures showing screen with no ribbons removed between the Tcon and panel. Next only the left ribbon removed and then finally the right only ribbon removed.

With the DVD player removed and using a scope, I can see data going from the main board to the Tcon when monitoring one of the data lines. Selecting and deselecting the Menu button on the remote flicks between the two screen shoots. The amplitude of the signal on the data line appears to be less than 0.5V and I am unsure if this is normal.

There is 12V dc on the Tcon board.

Suspect the Tcon needs to be replaced.

[comptek]

Re: LG LE37LH4000-ZA Tcon Issue?

study lvds cables to screen inspect them as you may have lifted trace cleaning them i have managed it once
as for the screen issue pretty common for tab bond failure

[ReeceyBurger123]

Re: LG LE37LH4000-ZA Tcon Issue?

Does look like Tcon to me, good method of diagnoses too I need to get a scope soon. Also check the Lvds signals coming out the Tcon after the amplifiers see if its similar to what the mainboard is outputting. Would you rather just replace it or try to debug it ?

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

Hello Comptex, That's the first thing I thought I may have done so I removed, inspected under a magnifying lamp, OK, then re-inserted the cables. Thanks for your input.

Hello ReeceyBurger123, That's the conclusion I reached but was ineterested in other peoples view. Thanks to for your input.

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

Hello ReeceyBurger,
I'd like to try and debug it since there's no fun in replacing it but I'm unfamiliar with their mode of operation so wouldn't really know where to start.
Thanks

[ReeceyBurger123]

Re: LG LE37LH4000-ZA Tcon Issue?

Will have a look see if I can find a schematic for this pcb.

[comptek]

Re: LG LE37LH4000-ZA Tcon Issue?

Hello Comptex, That's the first thing I thought I may have done so I removed, inspected under a magnifying lamp, OK, then re-inserted the cables. Thanks for your input.

Hello ReeceyBurger123, That's the conclusion I reached but was ineterested in other peoples view. Thanks to for your input.

ok cool

[ReeceyBurger123]

Re: LG LE37LH4000-ZA Tcon Issue?

When it comes on Dick does the little blue light come on ?

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

Initially it did. It would flash a few times. I need to take a look and see what state it is now and be back in a few mins.

[ReeceyBurger123]

Re: LG LE37LH4000-ZA Tcon Issue?

Ok one thing to check it the transistor Q401 underneath the blue Led that I belive fails on these. Not sure what it does as cant find any schematics for it.

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

When it comes on Dick does the little blue light come on ?

Not anymore. As I said when I powered it up "prior to cleaning the ribbons" I'm fairly certain it would flash quite a few times.

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

Thanks for the hint. This will be a job for the morning.

[ReeceyBurger123]

Re: LG LE37LH4000-ZA Tcon Issue?

The light should come on to show that the Tcon processor has been turned on, keep us updated bud

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

Will do

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

I've now had a chance to do a bit more checking on the Tcon board.

The blue light on the Tcon flashes only once but extremely briefly at switch on.
Lifted Q401(mosfet) out of circuit which checked OK.
Measured the voltages around the MAX17108 which is a 10 Channel High Voltage Scan Driver.

Gon1 = 26V
Goff = -9V
Gon2 = 26V

Pos = 6.8V (Opamp positive/ non-inverting input)
Neg = 6.8v (Opamp negative/inverting input)

The 8 pin IC's appear to be running at 3.3V

Looking at the data sheet for the panel LC370WUH (SB)(A1) I believe the above voltages are within the driving specification of the panel.

However, monitoring the inputs A1 through A10 of the MAX17108 IC, there appears to be no input signal and therefore no output signals at Y1 through Y10.

It looks as though the video signals has been lost somewhere between entering the Tcon board on route to the MAX17108 panel driver.

I have now ordered a replacement and will let you know the results.

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

Update:-

The replacement Tcon arrived today and the blue led on it does indeed stays on until the backlights fire up, then the picture, before it goes off.

The original fault described was that the picture is scrambled (see photo's) and this is still the case however it return to normal within a few minutes.

The set has to be off at least an hour or so before you can repeat the scrambled screen at switch on.

The only other hint is that while in the scrambled state the picture freezes when changing channels for 2 to 3 seconds. The sound is fine.

I've check the voltages of the main board regulators and they appear to be OK. 3.3V, 1.8V, 1.2V and 5V.

The power supply voltages read as given on the PSU label. 5.2V, 12V, 20V and they to read OK

Any suggestions welcome?

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

Here's a video link showing the fault as best I can.
I would be interested in your opinions as to whether or not it a video fault or a panel problem?

https://youtu.be/zzpYIInTmNY

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

Further update.

After gently warming up the circuit board connecting the panel to the tcon board with a hair dryer for a few minutes, the set turns on and behaves itself perfectly.

[ReeceyBurger123]

Re: LG LE37LH4000-ZA Tcon Issue?

Tab bond issue then bud.

[dick_barton]

Re: LG LE37LH4000-ZA Tcon Issue?

That was my fear too.
I'm hoping that pressure on the offending component may solve the problem. Warming up makes it work so I feel its a connection problem. Will take a look at the tab-panel board for any suspect joints as well.
Will let you know.