Lg 23lx1rv

[PlainBill]

This was a freebie from a member here, Thanks David!!!

My first reaction was indifference. It had a very unusual display problem (see attachments (I zipped the video)) which I tentatively felt was either tcon or panel, and the built in DVD player did not seem to be working, so I set it aside. When I checked the price of a tcon I discovered it would cost less than $20, so there was a potential profit to be made.

Before ordering a tcon, I examined the display again and realized it looked like it was missing sync signals. That would be the main board, and unreasonably expensive for a 23" TV. Then looking at the service manual I realized the DVI input went directly to the gm5221 chip. Hooking it up to a computer showed the same problem!!!

That reduced the possibilities - A bad gm5221 or a bad regulator. Power for the gm5221 comes from a pair of dedicated regulators 3.3 and 1.8 volts. The 3.3 read 3.31 volts, but the 1.8 read 1.76, slightly low. At this point I pulled out the scope and looked at the power supply lines. The 3.3 volt line was clean, but the 1.8 volt line had over 1V p-p of noise riding on it. The output of the 1.8 volt regulator was filtered by a pair of 47uF, 16V caps, so as a final step I tried hooking a 100uF, 25V cap in parallel with them. When I powered up the set I was happy to see a clean 1.8V rail, and a stable 'No Signal display on the screen. I pulled the original SMT caps and replaced them with a pair of 47uF low ESR caps and the TV is working perfectly.

The DVD problem turned out to be a combination of problems - the DVD player is disabled if it is not the selected input - and the DVD I was using for testing (E.T. - The Extraterrestial) was rejected by the player, while it found 'Knowing' perfectly acceptable.

PlainBill

[tom66]

Re: Lg 23lx1rv

Very strange. So the 47u/16V general purpose capacitors were failed? I would not have expected that...

[PlainBill]

Re: Lg 23lx1rv

Very strange. So the 47u/16V general purpose capacitors were failed? I would not have expected that...

I believe so. There was evidence to indicate something had vented in the area. The ESR tests indicated they were marginal (I don't have a capacitance meter that goes that high). I can't think of a failure mode for the regulator (a LD1086DT18) that would result in oscillations that could be eliminated that easily. The amplitude of the noise was about 1volt, if it was due to a failure of the regulator I would have expected it to be reduced by a low ESR cap, but not eliminated. A further indication - with the cap in place the voltage rose to 1.807 volts

PlainBill

[tom66]

Re: Lg 23lx1rv

I believe so. There was evidence to indicate something had vented in the area. The ESR tests indicated they were marginal (I don't have a capacitance meter that goes that high). I can't think of a failure mode for the regulator (a LD1086DT18) that would result in oscillations that could be eliminated that easily. The amplitude of the noise was about 1volt, if it was due to a failure of the regulator I would have expected it to be reduced by a low ESR cap, but not eliminated. A further indication - with the cap in place the voltage rose to 1.807 volts

PlainBill

I'm guessing that the voltage regulator was some kind of LDO. Most LDOs have a limited range of stability - they like an ESR between 0.2 and 4 ohms, for example. It's possible the cap's ESR exceeded this, causing the instability. Or, if there were other caps in parallel with the general purpose ones (for example for decoupling), it could reduce the apparent ESR, also causing instability.

Do you remember what frequency the ripple was at? Several kHz?

[PlainBill]

Re: Lg 23lx1rv

I'm guessing that the voltage regulator was some kind of LDO. Most LDOs have a limited range of stability - they like an ESR between 0.2 and 4 ohms, for example. It's possible the cap's ESR exceeded this, causing the instability. Or, if there were other caps in parallel with the general purpose ones (for example for decoupling), it could reduce the apparent ESR, also causing instability.

Do you remember what frequency the ripple was at? Several kHz?

The regulator is an LDO (1086 family) device. The noise wasn't ripple, it appeared to be a fairly broad spectrum.

PlainBill

[Paul678]

Re: Lg 23lx1rv

This was a freebie from a member here, Thanks David!!!

My first reaction was indifference. It had a very unusual display problem (see attachments (I zipped the video)) which I tentatively felt was either tcon or panel, and the built in DVD player did not seem to be working, so I set it aside. When I checked the price of a tcon I discovered it would cost less than $20, so there was a potential profit to be made.

Before ordering a tcon, I examined the display again and realized it looked like it was missing sync signals. That would be the main board, and unreasonably expensive for a 23" TV. Then looking at the service manual I realized the DVI input went directly to the gm5221 chip. Hooking it up to a computer showed the same problem!!!

That reduced the possibilities - A bad gm5221 or a bad regulator. Power for the gm5221 comes from a pair of dedicated regulators 3.3 and 1.8 volts. The 3.3 read 3.31 volts, but the 1.8 read 1.76, slightly low. At this point I pulled out the scope and looked at the power supply lines. The 3.3 volt line was clean, but the 1.8 volt line had over 1V p-p of noise riding on it. The output of the 1.8 volt regulator was filtered by a pair of 47uF, 16V caps, so as a final step I tried hooking a 100uF, 25V cap in parallel with them. When I powered up the set I was happy to see a clean 1.8V rail, and a stable 'No Signal display on the screen. I pulled the original SMT caps and replaced them with a pair of 47uF low ESR caps and the TV is working perfectly.

The DVD problem turned out to be a combination of problems - the DVD player is disabled if it is not the selected input - and the DVD I was using for testing (E.T. - The Extraterrestial) was rejected by the player, while it found 'Knowing' perfectly acceptable.

PlainBill

Bill, when you say, "I realized it looked like it was missing sync signals",
can you describe in more detail what you were seeing?

I imagine it's something like the picture rolling vertically, like when
you didn't have the vertical control adjusted properly in an older
CRT tv.

[PlainBill]

Re: Lg 23lx1rv

Bill, when you say, "I realized it looked like it was missing sync signals",
can you describe in more detail what you were seeing?

I imagine it's something like the picture rolling vertically, like when
you didn't have the vertical control adjusted properly in an older
CRT tv.

More or less. The picture would look like it was rolling vertically like we loved to see back in the days of vacuum tube TVs, but it also seemed to drift side to side at times.

PlainBill

[spinger]

Re: Lg 23lx1rv

Hello PlainBill.

I just wanted to thank you because you helped me solve a problem I had with this TV.

Thank you very much

[skullking123]

Re: Lg 23lx1rv

Hi guys I'm trying to find the capacitors that I need to change for this fix. I found the gm5521 chip but not sure which caps are the ones needing to be changed. A bit of a newbie so any help would be much appreciated.

Here's pic of the board:

[selldoor]

Re: Lg 23lx1rv

There are only 10 ordinary caps on the board. Plainbill seems to have changed the 47uf16v caps. You can either try just those or replace them all- have you checked the voltage regulators as he did? You dont say what is wrong with the set.
You should be able to get the caps at digikey - you dont say where you live - please update your profile with at least country and mains voltage. I would use panasonic Fm or Fr series if you can get them in the sizes you need - you also need to be sure you get the same (or smaller physical size so that they will fit the space.

[skullking123]

Re: Lg 23lx1rv

Oh sorry, the issue looks to be the exact as what Plainbill was experiencing. I meant to ask where to find the power regulators so I could test them and in turn find the correct capacitors to replace.

I have used digikey before but I would like to test the regulators before buying the caps.

Here's a pic of the power board in case it is needed:

[selldoor]

Re: Lg 23lx1rv

You need to read this
https://www.badcaps.net/forum/showthread.php?p=261329
I cannot identify all the regulators some look like regulators but you can only be sure by getting the part numbers and checking the datasheets.
As a start on the left in your pic just by the connector with alternate blue gray wires there is one LMS1587 3.3.

The power supply needs a good dusting with a soft brush
Please update your profile

[skullking123]

Re: Lg 23lx1rv

Thank you selldoor for that great tutorial. Had some time to check the regulators and their values were very similar to PlainBill's. The 3.3V regular was reading a 3.29V but the 1.8V regulator was reading 1.745V a tad bit less than what PlainBill was getting.

If I'm not mistaken I believe the 47uF 16V caps that PlainBill replaced include the cap under the bottom left corner of the gm5221 chip and the cap on to the bottom-left of that one. Looks like there are 2 traces coming out of the 1.8V regulator to those two caps.

Please let me know if you see it differently and also would appreciate some help finding the correct replacement caps.

[selldoor]

Re: Lg 23lx1rv

Cant tell could be either two of the four - I might be inclined to change all four and if it was a bad batch perhaps all the 16v47uf ones as postage may be your biggest outlay.
I think he didnt replace with SMT he used radial low esr ones.

[skullking123]

Re: Lg 23lx1rv

Went ahead and ordered the four since price isn't really an issue. Now just have to wait for them to arrive.

Thanks again for the help.

[skullking123]

Re: Lg 23lx1rv

Thought I would update. Caps arrived in mail today and I went ahead a replaced the two that I suspected were the cause. Turned it on and voila it's fixed.

Thanks again selldoor for the help and PlainBill for finding the fix.