LG flatron L1718S - shaky picture when not in native resolution

[tom66]

Re: LG flatron L1718S - shaky picture when not in native resolution

I changed two caps we were talking about and no change noted... Sadly I can;t seem to find this particular IC, that has output voltage of 1.8v. Closest is 3.3v.

Aly alternatives?

Look for AS1117, or LM1117, or LD1117, or AM1117. -18 is the output. Can eBay sellers ship to you? If so, http://www.ebay.co.uk/itm/2-x-SMD-SM...item3f06fd6467 or http://www.ebay.co.uk/itm/20x-AMS111...d#ht_779wt_956 (pack of 20, you'll be able to fix 19 more monitors. )

If not, you could do what I did to fix this 32" TV; I built a little regulator board (with an LM317T, cheap and plentiful device) and fitted it in the chassis. However, that TV had a lot of spare space inside; I'm not sure a 17" LCD would have enough space.

[bocca]

Re: LG flatron L1718S - shaky picture when not in native resolution

I changed two caps we were talking about and no change noted... Sadly I can;t seem to find this particular IC, that has output voltage of 1.8v. Closest is 3.3v.

Aly alternatives?

[bocca]

Re: LG flatron L1718S - shaky picture when not in native resolution

OK, i think i measured 102. It peaks to 1.60v for a brief moment and then drops to 0. Battery is stable 4v

[retiredcaps]

Re: LG flatron L1718S - shaky picture when not in native resolution

The datasheet doesn't mention a maximum input - I know some regulators are limited to just 6V in! - so try and stay within this limit.

Yes, I caught my own error after posting in post #15

Most of the time, I use *weak* 9V batteries. The one in the picture is 7.3V with no load. I find it easier to clip on leads versus doing multiple AA cells in series.

The voltage regualtor in the picture, obviously, is a fixed 3.3V. I do have a 1.8V, but the 3.3V is the one I had handy. Cloudy day so I had to use indoor flash so not my best work.

[Scenic]

Re: LG flatron L1718S - shaky picture when not in native resolution

In this application, Yageo may be okay. They are formerly Philips/Vishay caps so better than no-name junk.

Yageo = Teapo
The only thing that's different is the name. Even the series are identical.

For example:
Yageo SC PDF -> link
Teapo SC PDF -> link1 link2 (2 somewhat different versions of the same datasheet)

[bocca]

Re: LG flatron L1718S - shaky picture when not in native resolution

hahaha, you seem to love Serbia more than I do

Errr, yeah, about that stand. I never found that service manual, but did exactly the same thing as illustrated. My motive was "I'm either gonna take off this damn stand, or I'm gonna break the mother***ker, it's all the same at this point", having tried for about 2 hours

Thank you very much for the schematic. Tomorrow I'm getting two of the 22uf, 16v and I'll see if that fixes the problem

[mockingbird]

Re: LG flatron L1718S - shaky picture when not in native resolution

@mockingbird:
That would be great, mate! I appriciate it

Hello to you in Serbia. Long live Serbia!

I just want to say that whoever designed this one was a masochist. I've taken apart LG screens before, with this one, I couldn't figure it out until finally I found the service manual and this important picture:



Ok firstly, the PSU:



Circled are the two groups of pi filters. We can do a little better spec-wise and matching the ESR:
1) 25V 1000uF 13x21mm - Replacement
2) 25V 470uF 10x16mm - Replacement
3) 35V 150uF 8x12mm - Replacement

1) 10V 1000uF 10x16mm - Replacement
2) 10V 1000uF 10x16mm - Replacement
3) 35V 150uF 8x12mm - Replacement

For the 25V 47uF caps, you can use anything, but it's best to use a
high quality cap (Don't forget to get 4 of these).

For the logic board, here are the caps:
1 x 16V 220uF 6.3x11mm
2 x 25V 10uF 5x11mm
2 x 16V 100uF 5x11mm
5 x 16V 22uF 5x11mm

Good luck.

[tom66]

Re: LG flatron L1718S - shaky picture when not in native resolution

You're lucky to even have electronic parts shops, in the UK the only one left is Maplin and they only seem to sell disco lights and car stereos!

If you record the series on the capacitor (something like two to three characters) then the ESR can be looked up.

[bocca]

Re: LG flatron L1718S - shaky picture when not in native resolution

I found them. There's two of 'em, both 22uf 25v. As far as I can see no ESR stated on them. Only other marking except temp rating (105) is 0627(M). Guess that's model.

@tom66:
Don't have the datasheet. Sore i found them in is small. They don't even have the website. I'll go there tomorrow to try to find the right ones. Sadly, any kind of online shopping is a thing of imagination here, so there's 4-5 stores to buy from and that's it.

@retiredcaps:
Found the battery of one cell phone which give 4.12v constantly (good battery, smashed phone) so i tried with it but it's fat too complicated to connect to board. I'll think of some other way

[Th3_uN1Qu3]

Re: LG flatron L1718S - shaky picture when not in native resolution

Will do. Just need to find the right one, or maybe I will replace them all. Any idea how to find the exact one of that regulator?

Probe around with your multimeter set to continuity mode (buzzer). One lead on the output of the regulator, with the other lead check the + of nearby capacitors. Hold the probe at least 5 seconds on each lead to avoid false detection. Some caps not actually connected to that trace will charge from the current provided by your multimeter, making it beep for the first couple seconds, then it'll read disconnected. When it keeps beeping after a few seconds, and also beeps when the test leads are switched around, you've found it.

Alternatively you can probe with the monitor on, and see which cap you get the 1.63 volts on.

[tom66]

Re: LG flatron L1718S - shaky picture when not in native resolution

ufff, good caps are almosty impossible to find in this hellhole I live in, and no one ships to serbia without at least 50 bucks worth of postage costs so that's out of option.
Best caps I can find are Yageo. Haven't found anything better for now.

BTW, how do I find ESR of the cap if it's not written on it?

In this application, Yageo may be okay. They are formerly Philips/Vishay caps so better than no-name junk. Do you have a datasheet for the caps in question?

[bocca]

Re: LG flatron L1718S - shaky picture when not in native resolution

@retiredcaps:
will do that right now! thanks

@tom66:
ufff, good caps are almosty impossible to find in this hellhole I live in, and no one ships to serbia without at least 50 bucks worth of postage costs so that's out of option.
Best caps I can find are Yageo. Haven't found anything better for now.

BTW, how do I find ESR of the cap if it's not written on it?

[tom66]

Re: LG flatron L1718S - shaky picture when not in native resolution

Alternatively, you can disconnect the power supply and apply a 9V battery battery directly to pin 3 and measure the output of pin 2 and see if it is 1.8V DC or not. Pin 1 is GND.

Only do this if the regulator can withstand 9V input and power dissipation is not exceeded.

Power dissipated is approximately (Vin - Vout) * Iout.

The scaler probably draws around 200mA and assuming maximum 1W dissipation for a temporary test:

Max Vin = 6.8

I would use two AA's in series, not a 9V battery.

The datasheet doesn't mention a maximum input - I know some regulators are limited to just 6V in! - so try and stay within this limit.

[tom66]

Re: LG flatron L1718S - shaky picture when not in native resolution

PlainBill had a similar problem with an LG TV: https://www.badcaps.net/forum/showth...&highlight=ldo

1.8V regulator read slightly low (1.76V)... Coincidence...? Turned out to be a bad cap on the LDO output causing some oscillating weirdness on the output. Some LDO regulators have an ESR requirement something like 1 ohm < ESR < 10 ohms. So replace any cap on the LDO output with a general purpose one (not low-ESR) with ESR within the range specified.

The datasheet says "The recommended value for ESR is 0.5 ohms." So I would find a decent Panasonic NHG cap to replace it with ESR and capacitance closely matching.

[retiredcaps]

Re: LG flatron L1718S - shaky picture when not in native resolution

@retiredcaps:
edit: 9V battery is so hard to find here, I'll sooner find caps and regulator and replace them. But thanks thou', interesting technique. I'll sure do good to remember it!

Sorry, I meant 2 AA cells in series for a total of 3.0+ V DC.

[bocca]

Re: LG flatron L1718S - shaky picture when not in native resolution

@retiredcaps:
Thanks. Seems you are right. Will try the caps first and if that doesn't do, I'll search for the new regulator.
edit: 9V battery is so hard to find here, I'll sooner find caps and regulator and replace them. But thanks thou', interesting technique. I'll sure do good to remember it!

@Th3_uN1Qu3:
Will do. Just need to find the right one, or maybe I will replace them all. Any idea how to find the exact one of that regulator?

@mockingbird:
That would be great, mate! I appriciate it

[retiredcaps]

Re: LG flatron L1718S - shaky picture when not in native resolution

Before replacing the regulator try replacing the output capacitor of that regulator, bad caps on reg outputs will give lowered voltage and a whole slew of issues. Had one monitor that put on all kinds of psychedelic color shows because of a bad cap on - coincidence - the 1.8v reg.

Alternatively, you can disconnect the power supply and apply a 9V battery battery directly to pin 3 and measure the output of pin 2 and see if it is 1.8V DC or not. Pin 1 is GND.

[mockingbird]

Re: LG flatron L1718S - shaky picture when not in native resolution

I just got one of these yesterday. If you want, I can give you a list of capacitors to use to replace the ones on the PSU and the logic board... This model uses all Su'scon caps.

[Th3_uN1Qu3]

Re: LG flatron L1718S - shaky picture when not in native resolution

Before replacing the regulator try replacing the output capacitor of that regulator, bad caps on reg outputs will give lowered voltage and a whole slew of issues. Had one monitor that put on all kinds of psychedelic color shows because of a bad cap on - coincidence - the 1.8v reg.

[retiredcaps]

Re: LG flatron L1718S - shaky picture when not in native resolution

U102 - part number:
A1
AS1117L-18
B0544

pin 1 = 0.00 V,
pin 2 = 1.63 V,
pin 3 = 5.17 V

U102 is bad. The -18 in the part number denotes the output voltage should be 1.8V DC. Most regulators are +/- 1% tolerance suggesting a good regulator is

1.8 x 0.99 = 1.782
1.8 x 1.01 = 1.818

Your regulator is (1.8 - 1.63)/(1.8*100) = 94.4% or more than 5% out. Replace it and hopefully that will solve your problem.