LG Flatron L17NT-A no power

[Rtech]

Re: LG Flatron L17NT-A no power

U801 is 3.3v low dropout Voltage regulator,the centre pin being Gnd,the lefthand one Input and the other one Output.They do go faulty and could be causing your problem.You can test it if you lift the two outside pins and then with nothing connected to the Board,you could apply a Dc Voltage greater than 3.3 v between input and Ground,and then measure the output, if that is the 3.3v it is supposed to give then, my best guess would be that the Logic Board is faulty. If you have a 3.3v fixed regulator then you could change it, and see what happens !!

[budm]

Re: LG Flatron L17NT-A no power

Diconnect the cable to the LCD panel and see if the 5V will recover. Something on the logic board or the T-CON on the LCD panel is loading down the 5V line badly or the 5V power supply is weak and cannot handle the load. You can also check the resistance reading on Pin 6 and ground with all the boards connected and see if it shows real low resistance.

[atanas18]

Re: LG Flatron L17NT-A no power

Hi guys.

U801 is 3.3v low dropout Voltage regulator,the centre pin being Gnd,the lefthand one Input and the other one Output.They do go faulty and could be causing your problem.You can test it if you lift the two outside pins and then with nothing connected to the Board,you could apply a Dc Voltage greater than 3.3 v between input and Ground,and then measure the output, if that is the 3.3v it is supposed to give then, my best guess would be that the Logic Board is faulty. If you have a 3.3v fixed regulator then you could change it, and see what happens !!

Yes, I know the value it should have at the output. However, I have to desolder this component to test it, but I don't have the right equipment to do it For this one I may go to some electronic service to do this test for me.

Diconnect the cable to the LCD panel and see if the 5V will recover. Something on the logic board or the T-CON on the LCD panel is loading down the 5V line badly or the 5V power supply is weak and cannot handle the load. You can also check the resistance reading on Pin 6 and ground with all the boards connected and see if it shows real low resistance.

I try this case (not connected to the LCD panel), but the voltages still drop off. So, with or without the LCD panel the voltages continue to drop.
About the resistance on pin6 against the ground, I hope I will have a time to test it tomorrow.

[goop]

Re: LG Flatron L17NT-A no power

They are all Samxon, all 105°C6, and all GF(M) unless otherwise noted:
(2) 1000μf, 16v, C6A, 10mmx20mm

(2) 1000μf, 16v, P12366-ND EEU-FM1C102 @ $.59 ea

Isn't the ESR on the Panasonic FM too low compared with the Samxon GF?
The figure I see for the Samxon GF 1000uf 16v 10x16 is 60mO. Assuming the 10x20 is a bit lower, it's still twice or more than the FM's 19mO.

If the FM is okay, will FJ's 13mO do as well? (Though, I'm looking at old and used caps, so probably higher?)

While at it, on the Samxons, does the M in GF(M) indicate 20% tolerance? And what are the 3 letter codes, such as V5A, V4A, C6A?

[goop]

Re: LG Flatron L17NT-A no power

In the meantime I replaced the a bulgy Samxon GF 1000uf/16V (C204) with the harvested FJ. It's enough to get it to turn on and show something on screen. I'll check it in more detail later.

Still I wonder about the lower ESR.

[budm]

Re: LG Flatron L17NT-A no power

Switching power supply for monitor is not going too care about lower ESR rating caps, it is not tightly regulated power supply.
I use FM/FC/FR series for all my repair works.

[goop]

Re: LG Flatron L17NT-A no power

What makes a monitor PSU different from an ATX PSU? Don't the logic board or panel need stable 5V/12V/-5V just the same?

[budm]

Re: LG Flatron L17NT-A no power

There are regulator ICs, buck switching regulators on the main board, also on the T-CON board on the LCD panel, the logic board also do not run on Giga Hertz frequency, mos are less than 10MHz.
Power supply in the monitor only have to put out 5V for running the main board and T-CON, and 12~20V for the backlights inverter circuits.

[goop]

Re: LG Flatron L17NT-A no power

Thanks. I think I'll start a dedicated topic to get more details.