LG flatron L1718S - shaky picture when not in native resolution

[bocca]

Hi!

So I have one of these, and it's got a shaky picture when not in native resolution, which is 1280x1024 btw. In a matter of fact, any 1280xXXX resolution stops the shaking and makes picture normal.

I looked over the PCB, ali it looks ok. No bulging caps, no busted fuses.

If you need a video of the thing, i'll make it.

Here's a pic of the PCB attached

[selldoor]

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

Hi - so what resolution did you want to use?
Did you try changing the refresh rate?
What Video card are you using?
What OS are you using?

Have you got the correct drivers for the Video Card and for the monitor/system.

Can you try the monitor on a different sytem.

Did it just start doing this or is it a new to you monitor

[bocca]

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

1. 1024x768, 800x600, it's all the same. As I said any 1280px by long side works fine
2. Yup. Tried 60hz, 75hz, no difference
3. Tried several of them, no change. Some are middle class, some are strong gaming ones
4. win xp
5. yes, drivers are correct. Problem is not software based, i'm pretty sure
6. tried it, no difference
7. Old problem. Monitor stood on a shelf for half a year, and now I tried to repair it.

thanks for replying

[retiredcaps]

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

1) Post a picture of your logic board. There may be some voltage regulators that are failing?

2) Are your voltages on the power board stable? I see the connector says 5V DC. Is that stable going to the logic board?

[Th3_uN1Qu3]

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

That is usually the fault of a bad cable, or weak signal coming from the video card. Before messing around inside the monitor, have you tried another cable and another computer?

[bocca]

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

@retiredcaps:

i attached the logic board photo

i measured the two voltages, and they are both 5.21v. seems normal to me

@Th3_uN1Qu3

i tried few cables, including test cable that's 100% working. As i previously said, tred switching video cards but to no avail. I also tried another computer completely.


One thing i noticed is, when i switch refresh rate from 75 to 60 hz shaking is reduced by about half but still clearly visible across whole screen

[bocca]

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

Just to note one more thing. When I enter the display menu, the menu part is not shaky but normal

[retiredcaps]

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

@retiredcaps:

i attached the logic board photo

U101 and U102 are your voltage regulators.

1) Put your multimeter on 20 V DC if manual range.

2) Put your black probe on a ground screw (any one on the logic board will do fine).

3) Put your red probe on each voltage regulator pin EXCEPT the big fat tab. If the middle pin is "cut" and not touching the board, we want to measure that pin as well.

4) Report the part number for each regulator.

5) Report all your findings like the following example,

U101 - part number AL1117-33
pin 1 = 0.00 V,
pin 2 = 3.3 V,
pin 3 = 5.0 V

[bocca]

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

U101 - part number:
A1
AS1117L-33
B0612

pin 1 = 0.00 V,
pin 2 = 3.28 V,
pin 3 = 5.19 V


U102 - part number:
A1
AS1117L-18
B0544

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

[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.

[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.

[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.

[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.

[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

@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.

[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.

[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.

[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

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?

[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.