Hyundai L90D+ inverter mosfet problem

[camra88]

Re: Hyundai L90D+ inverter mosfet problem

Results:

all caps and Q's are not short circuited. Including C22 & C52.

All resistors are within tolerances

All diodes? (D's) also pass this test, except for 2:

D14 and D16 (to the left of the 0Z960SN) -- i get a reading of 98 ohms across the two legs next to each other. They are the legs connected in parallel to a 390 ohm resistor (according to marking 3900).

I find this low, considering measurements taken off similar D's: D10 and D11 (they all have similar markings A7>) measured at 1k ohms. (390 || 1000) = 280 ohms. Is this a normal in-circuit resistance at those two nodes?

[retiredcaps]

Re: Hyundai L90D+ inverter mosfet problem

D14 and D16 (to the left of the 0Z960SN) -- i get a reading of 98 ohms across the two legs next to each other. They are the legs connected in parallel to a 390 ohm resistor (according to marking 3900).

Personally, I would change the caps first and retest. However, if you have really good soldering skills and can remove D14 and D16 without destroying them, you can test them out of circuit. In circuit testing can be affected by surrounding components.

My soldering skills for something that small dictates that I try new caps first.

[camra88]

Re: Hyundai L90D+ inverter mosfet problem

I replaced those caps with 25v, 330uF's. Problem remains.

I also noticed that when I first turn the monitor on, the backlight flickers for only a quick moment. I didn't notice it until I turned the lights off in the room.

After turning it on and off many times to observe this just now (about a dozen+ times), the monitor turns off once it attempts to power up the backlight. If I give it a minute, it will stay on again. I don't know if this means anything?

Knowing this, can I pinpoint the culprit?

Thanks

[jetadm123]

Re: Hyundai L90D+ inverter mosfet problem

I replaced those caps with 25v, 330uF's. Problem remains.

I also noticed that when I first turn the monitor on, the backlight flickers for only a quick moment. I didn't notice it until I turned the lights off in the room.

After turning it on and off many times to observe this just now (about a dozen+ times), the monitor turns off once it attempts to power up the backlight. If I give it a minute, it will stay on again. I don't know if this means anything?

Knowing this, can I pinpoint the culprit?

Thanks

Since you're getting a flicker of the backlight before shutdown, this could be caused by:

1) Bad wiring to the CCFL tube(s)

2) Bad CCFL tube

3) Bad inverter transformer


To check the CCFL tube, you'll have to find a known good one and susbstitute for the existing tube.

Check the resistance of the secondary for each inverter transformer. There should be no more than 3% difference between the two.

[retiredcaps]

Re: Hyundai L90D+ inverter mosfet problem

Check the resistance of the secondary for each inverter transformer. There should be no more than 3% difference between the two.

I circled the inverter transformer secondaries. With power off and lcd unplugged, set your multimeter to 2000 ohms (if manual).

Measure the resistance between the 2 red dots. Report measurement. Do the same for the blue dots.

[rurban]

Re: Hyundai L90D+ inverter mosfet problem

I have a mildly off-topic contribution to this thread...
my L90D+ exhibited similar problems (power light flashed orange briefly then went back to blue, accompanied by a quiet clicking sound). I found a used power-supply in china and had it sent to me, which took 3 months. The PS was functional, but it already had a brown burn mark on the component side opposite one of the inverter MOSFETs.

I fashioned a heat-spreader and siliconed it to the PC-board to get the most out of the used PS. Picture below.

I also removed the plastic enclosure around the PS, and instead glued a piece of plastic to the back of the panel opposite the PS, in order to improve air circulation.

R. Urban

[Sharky-T]

Re: Hyundai L90D+ inverter mosfet problem

[QUOTE=retiredcaps;119680]In post #1, it is picture 3. U5 to the right of the circled component. U4 is to the left of it. Both are 6 pins.

Hi... even though some years back, I wonder about the statement:

"Both are 6 pins."

On my board, U5 and U4 are 8 pins.

I am a bit confused.

[Sharky-T]

Re: Hyundai L90D+ inverter mosfet problem

[QUOTE=retiredcaps;119680]In post #1, it is picture 3. U5 to the right of the circled component. U4 is to the left of it. Both are 6 pins.

Hi... even though some years back, I wonder about the statement:

"Both are 6 pins."

On my board, U5 and U4 are 8 pins.

I am a bit confused.

[selldoor]

Re: Hyundai L90D+ inverter mosfet problem

[QUOTE=Sharky-T;499901]

In post #1, it is picture 3. U5 to the right of the circled component. U4 is to the left of it. Both are 6 pins.

Hi... even though some years back, I wonder about the statement:

"Both are 6 pins."

On my board, U5 and U4 are 8 pins.

I am a bit confused.

There are 8 pins on the original picture - probably just a typing error.
retiredcaps also posted the datasheets which show 8 pins.

Retiredcaps used to help out on here for hours on end and it does go for the eyes. I personally work on a small laptop and can barely tell the difference
between the 6 and 8 on my keyboard .

Even if it was noticed later, one cannot amend posts after around 1 hour.