LG 37LC2D No picture, believe bad power supply

[tom66]

Re: LG 37LC2D No picture, believe bad power supply

"UD" just means a specific version for the US market. For example, the default language may be American English or it may have one more component input and no SCART ports on the main board. The power supplies are the same between all models.

I've had a look, and the service manual I have doesn't have a power supply schematic. It does include schematics for the main board but nothing else. Can you upload your one you're working on, in case it does have such a schematic?

[millennia]

Re: LG 37LC2D No picture, believe bad power supply

Sure, see attached for the one I am referring to. I guess your comment verifies the fact that I can find some but not all parts references to the board. I have downloaded a few 37" manuals but this seems to be the closest match, but not enough help for me.

Page 56 in the upper left corner is the only info I can find. My D200 has 5V coming off the center pin, C202 was replaced with the cap set and shows 5.2, cannot find any other parts listed. When I try to trace the back of the board I think I see where all the 6V connector outputs are coming from a common source, all of which seems dead. I was contemplating putting an external 6V input on the pins while the unit is powered up to see if it helped but afraid it might blow something else.

[tom66]

Re: LG 37LC2D No picture, believe bad power supply

No PSU schematics there, then.
I would suggest it's likely the buck regulator IC.
https://www.badcaps.net/forum/attach...8&d=1367758731

3.4V converter is on the left, that's the three 8-legged chips. The 6V converter is on the right, also three chips. For the 6V output, it's the lower most chip. You can try comparing this to the left-most chip in the 3.4V block. If you check each pin voltage they should be more or less the same as each other.

[millennia]

Re: LG 37LC2D No picture, believe bad power supply

Measurements for those are:

For the 3.4 converter on left side:
Top chip - Q209
0 0 0 0
11 11 11 11

Mid - Q210
0 0 0 0
0 0 0 0

Bottom - U204
2.9 2.9 17.5 0
0 11.3 0 0

6V Converter on the right side:
Left - U200
0 2.3 9.3 0
0 5.1 .9 0

Mid - Q204
5.2 3 3 3
1.2 0 0 0

Right - Q205
3.3 3.3 3.3 3.3
0 0 0 0

Hmmmmm, readings seem to be all over the map to me.

[tom66]

Re: LG 37LC2D No picture, believe bad power supply

I have a feeling Q210 may be shorted. Disconnect power from the board, wait a few minutes, then test resistance between each opposite pin. (e.g. 1-8, 2-7, ...)

[millennia]

Re: LG 37LC2D No picture, believe bad power supply

I have a feeling Q210 may be shorted. Disconnect power from the board, wait a few minutes, then test resistance between each opposite pin. (e.g. 1-8, 2-7, ...)

All of the Q's and U's for 3.4 and 6 sections check the same way, OPEN, no matter how they are tested in the board. Removed all connectors and they still show same reading. Probably getting interference through other components so the only way to properly test would be to remove them(?). Q210, the middle one of the left, has all 4 inputs (5-8) soldered together so whatever comes in or out that side will be the same.

[tom66]

Re: LG 37LC2D No picture, believe bad power supply

If Q210 is not shorted, then it is probably the control IC, U200. Can you read off the part # on U200?

[millennia]

Re: LG 37LC2D No picture, believe bad power supply

Both U200 and U204 share the same part numbers:

3037CS
613P IOR
CD4W6

[tom66]

Re: LG 37LC2D No picture, believe bad power supply

A lot of people have this problem, here is one diagram someone made.
http://farm8.staticflickr.com/7016/6...bcedf382_z.jpg

The IC 3037CS is available for around £1.50 (~$2.40) on eBay, so I would suggest swapping it.

[millennia]

Re: LG 37LC2D No picture, believe bad power supply

A lot of people have this problem, here is one diagram someone made.
http://farm8.staticflickr.com/7016/6...bcedf382_z.jpg

The IC 3037CS is available for around £1.50 (~$2.40) on eBay, so I would suggest swapping it.

Thanks for all your assistance, I will get the replacement part and attempt a repair.

[godzzila]

Re: LG 37LC2D No picture, believe bad power supply

I have the same problem... +3.4V line is only +2,4V.. all caps ok SO is it enough to replace only 3037CS controller IC? Thanks for the info.

Or can I inject 3,3V externally for test if it will work?
Mine no sound.. picture distoret, lines etc no buttons work.. +3.4V line low other voltages fain.

[tom66]

Re: LG 37LC2D No picture, believe bad power supply

I have injected 3.4V in before with success, to prove power board bad, so trying it can't hurt.

[godzzila]

Re: LG 37LC2D No picture, believe bad power supply

Ok I tried that and it didnt change anything..
Still only lines on screen and no sound. All voltages ok.. seems like bad motherboard?
I tried analog dvd player, ps3 on hdmi etc but no sound.

[tom66]

Re: LG 37LC2D No picture, believe bad power supply

Did you check the 6V and 3.4V lines measure good now? It could be that bad 3.4V section of PSU loads down your external 3.4V.

[godzzila]

Re: LG 37LC2D No picture, believe bad power supply

As I said all voltages just fain 6,1V and 3,4V injected from power supply.
Tested again with multimeter and all ok but problem is the same.

[godzzila]

Re: LG 37LC2D No picture, believe bad power supply

TV show only this... and no sound no anything else.. and picture is freezed no change.

[tom66]

Re: LG 37LC2D No picture, believe bad power supply

Can you see what current is being drawn on 3.4V?
From what I remember, the 37LC2D I worked on drew about 1.3~1.4A on that rail.

[godzzila]

Re: LG 37LC2D No picture, believe bad power supply

yes current around 1,5A when its powered up and around 0,7A in stby

[tom66]

Re: LG 37LC2D No picture, believe bad power supply

OK, what is the voltage at the points marked 12V? Also, I think there is a 19V rail on this set but can't remember. If there is, check that too.

[godzzila]

Re: LG 37LC2D No picture, believe bad power supply

As I said ALL voltages ok.. 19-18,9V 12-11,9V all just fain really.