LG 37LC2D No picture, believe bad power supply

[DakotaKid]

I have an LG 37LC2D LCD TV that began shutting down and now won't display a picture. When you turn it on, the green power LED flashed about 14 or 15 times then stays on steady. The screen is lit but all black and the remote can only turn the TV off. In addition, the side controls on the TV do not work so it is not possible to change inputs, etc. Sometimes the TV will flash black and gray alternating. It was coming on after about a half hour of being powered up but it is no longer doing that.

I took the back off and as I expected, found a bulging capacitor on the power supply (PSU part number 6709900016D). It is C208 100uF 16V. I replace that cap but it didn't fix the problem so I am thinking I probably need to replace more of the caps even though they are not bulging. The output voltages are as follows:
should be 3.3V is actually 2.65V
6V is 6V
12V is 11.7V
19V is 18.7V
5V is 5V

Do I need to replace all of the smaller voltage caps or should I be looking for a different problem?

Thanks.
DK

[retiredcaps]

Originally Posted by DakotaKid

I replace that cap but it didn't fix the problem so I am thinking I probably need to replace more of the caps even though they are not bulging. The output voltages are as follows:
should be 3.3V is actually 2.65V
6V is 6V
12V is 11.7V
19V is 18.7V
5V is 5V

1) The standard advice is to replace all the caps on the power supply especially if they made by poor manufacturers like Capxon.

[/start cookie cutter answer]

Capacitors die from age, heat, and shoddy build quality. Capacitors DO NOT have to be visibly bloated in order to bad. They can be out of tolerance uF (a 1000uF measures 20uF) and/or have high ESR (ohm). A multimeter will be insufficient to test for ESR. For that you need an ESR tester which costs between $50 and $300.

[/end cookie cutter answer]

2) Where is your 3.3 V DC low? Is it on the power supply or main board? If it is on the main board, you may have bad caps and/or a bad voltage regulator.

[DakotaKid]

Thanks retired!

It looks like most are Samxon. There are 19 caps total, 2 of which are 450V, 4 are 50V and the rest are 35V down to 10V. I will probably start with all of the caps on the secondary side which is 12 total and see what that does for me. I either have those or they are readily available to me.

Should I "up" the voltage one step on the 10V and 16V to give myself a better cushion or just go back with what it has now? It seems these 10V and 16V are the most prone to early failure.

Thanks again for all the help.
DK

[tom66]

Might be a bad cap in the 3.3V supply. I had an LG LCD TV (model 42LC46) which had a bad cap there. Post a picture of the power board, it should be possible to see where the 3.3V buck converter is. Almost all LG LCD TVs and most of their plasmas I have seen use a separate buck converter for the 3.3V rail which is on the power supply.

[DakotaKid]

Picture attached. The bulging cap I replaced was 3rd from left in the line of caps on the lower right row in the picture, between the heat sink and the connectors. The voltage readings were on the pinouts of these connectors.

Thanks.

[tom66]

I'm not seeing a 3.3V buck converter which is strange. Can you post a picture of the underside of the board?

[DakotaKid]

Originally Posted by tom66

I'm not seeing a 3.3V buck converter which is strange. Can you post a picture of the underside of the board?

I will take a picture but there is nothing on the bottom but solder joints and traces, definitely no large components.

Thanks.

[tom66]

Originally Posted by DakotaKid

I will take a picture but there is nothing on the bottom but solder joints and traces, definitely no components.

Thanks.

Huh. Okay then, have you replaced the capacitor on the 3.3V rail? (You can identify it by following traces from the 3.3V output.) Some capacitors fail without bulging. (CapXon is well known to do this.)

[DakotaKid]

I uploaded the picture and looks like you responded meantime. Also, when i said "no components" I meant "no large components" e.g. capacitors. There are definitely some surface mount devices on the bottom of the board. The large black square is a foam pad, I presume just to give the middle of the board some support. The traces are hard to follow but it doesn't look like the cap I replaced was directly in the 3.3V circuit so I think I probably need to tackle a few more of the caps.

If you zoom on the picture of the bottom, the red spots are where I replaced C208, the yellow spots are the terminals for the 3.3V connections.

Should I use higher voltages or will replacing with new and better quality be sufficient?

Thanks.

[tom66]

Originally Posted by DakotaKid

I uploaded the picture and looks like you responded meantime. Also, when i said "no components" I meant "no large components" e.g. capacitors. There are definitely some surface mount devices on the bottom of the board. The large black square is a foam pad, I presume just to give the middle of the board some support. The traces are hard to follow but it doesn't look like the cap I replaced was directly in the 3.3V circuit so I think I probably need to tackle a few more of the caps.

If you zoom on the picture of the bottom, the red spots are where I replaced C208, the yellow spots are the terminals for the 3.3V connections.

Should I use higher voltages or will replacing with new and better quality be sufficient?

Thanks.

A 6.3V capacitor will be fine. Most modern capacitors are not adversely affected but voltages up to their nominal.

[DakotaKid]

I have ordered the set of caps I need. Thanks again for the assistance and advice.

[DakotaKid]

Replaced all of the caps on the secondary side of the power supply and it's working perfectly again! Thanks for the help.

[retiredcaps]

So I guess 3.3 VDC is 3.3 VDC and not 2.6 VDC now?

[DakotaKid]

Correct. This supports your advice about not just replacing the visibly failed (leaking or bulging) caps but rather go ahead and replace all of them, especially if they are inferior brand to begin with.

Most of what I replaced were originally Samxon, I went back in with Nichicon and Panasonic.

[retiredcaps]

Originally Posted by DakotaKid

Most of what I replaced were originally Samxon,

Samxon GF series are problematic. Other Samxon may be okay.

[DakotaKid]

<deleted>

[ibis]

I found this conversation helpfull since I experience the same problem with this model tv. Exactly which caps must be replaced and where are they located?

[DakotaKid]

Originally Posted by ibis

I found this conversation helpfull since I experience the same problem with this model tv. Exactly which caps must be replaced and where are they located?

If you pull up the picture of the PS board from post #5, I replaced all of the caps on the lower right row, alongside the heat sink. I believe I replaced the caps to the right of the transformer two, between the two heat sinks. At a minimum, I'd recommend all of them in that row on the lower right. That is where the 3.3V and 5V connections are that are likely causing your problems.

[phivophor]

...so I've got an LC 37LC2D with the same NON-OP symptoms this thread describes...I've pulled the Power Supply board and yes, referencing POST#5, several of the caps in the lower right hand string of (8) definitely have 'bulging' tops. They are all SAMXON...Matching the Capacitance, Voltage, Temperature and Physical Size parameters via badcaps.net doesn't appear to be an issue, it's the Manufacturer and ESR (GK,GF,GE,KM) ratings that don't seem to line up. Would anyone know if these will be a significant issue for this application?

[PlainBill]

Originally Posted by phivophor

...so I've got an LC 37LC2D with the same NON-OP symptoms this thread describes...I've pulled the Power Supply board and yes, referencing POST#5, several of the caps in the lower right hand string of (8) definitely have 'bulging' tops. They are all SAMXON...Matching the Capacitance, Voltage, Temperature and Physical Size parameters via badcaps.net doesn't appear to be an issue, it's the Manufacturer and ESR (GK,GF,GE,KM) ratings that don't seem to line up. Would anyone know if these will be a significant issue for this application?

Samxon has had issues with some series of caps. If the tops are bulging, they are bad. Replace them with name brand low ESR caps, such as Panasonic FM or FR series.

PlainBill