Gateway FPD1976w / LE1936 Inverter Madness

[boomer9999]

Hi,

I'm new here. Working on my first LCD repair!!

OK, it is opened up on the bench. Power on the display, the lamps in the panel power up for about 1 sec. then turn off, then turn on for about 1 sec. then remain off. The blue led power button remains on. (display from PC is working correctly and is visible with flashlight when inverter is down)

All caps look fine on the outside. Scoped the DC and everything is smooth.

I tacked a 1 meg resistor from vsense on pwm to ground to keep the inverter running. 1 of the 2 inverter transformers gets very hot and the waveforms on the mosfet drive have huge 100 volt spikes on the leading edge of both half of the primary side of inverter. The other transformer has clean signals. Bringing the scope near the HV traces shows the hot transformer is got the same output as the cool one - a nice sinewave.

This is the board I'm dealing with:
https://www.badcaps.net/forum/attach...1&d=1303052623

I have tried replacing one cap at a time with the spares I have and there is no change.

Help

[boomer9999]

Re: Gateway FPD1976w / LE1936 Inverter Madness

Hi,

I'm new here. Working on my first LCD repair!!

OK, it is opened up on the bench. Power on the display, the lamps in the panel power up for about 1 sec. then turn off, then turn on for about 1 sec. then remain off. The blue led power button remains on. (display from PC is working correctly and is visible with flashlight when inverter is down)

All caps look fine on the outside. Scoped the DC and everything is smooth.

I tacked a 1 meg resistor from vsense on pwm to ground to keep the inverter running. 1 of the 2 inverter transformers gets very hot and the waveforms on the mosfet drive have huge 100 volt spikes on the leading edge of both half of the primary side of inverter. The other transformer has clean signals. Bringing the scope near the HV traces shows the hot transformer is got the same output as the cool one - a nice sinewave.

This is the board I'm dealing with:
https://www.badcaps.net/forum/attach...1&d=1303052623

I have tried replacing one cap at a time with the spares I have and there is no change.

Help

I just noticed that the lamp that the hot transformer is running is also way too hot at the ends.

[PlainBill]

Re: Gateway FPD1976w / LE1936 Inverter Madness

Hi,

I'm new here. Working on my first LCD repair!!

OK, it is opened up on the bench. Power on the display, the lamps in the panel power up for about 1 sec. then turn off, then turn on for about 1 sec. then remain off. The blue led power button remains on. (display from PC is working correctly and is visible with flashlight when inverter is down)

All caps look fine on the outside. Scoped the DC and everything is smooth.

I tacked a 1 meg resistor from vsense on pwm to ground to keep the inverter running. 1 of the 2 inverter transformers gets very hot and the waveforms on the mosfet drive have huge 100 volt spikes on the leading edge of both half of the primary side of inverter. The other transformer has clean signals. Bringing the scope near the HV traces shows the hot transformer is got the same output as the cool one - a nice sinewave.

This is the board I'm dealing with:
https://www.badcaps.net/forum/attach...1&d=1303052623

I have tried replacing one cap at a time with the spares I have and there is no change.

Help

The hot transformer indicates a problem (Duh!!! - Like you didn't know that already!)

1. Measure the secondary resistances of the two transformers. If they don't match, the one with the lower resistance is shorted.

2. Swap the CCFL leads that normally go to the 'hot' transformer to the 'cool' transformer and vice versa. If the same transformer does not get hot it's a problem with CCFLs or leads. If the same 'hot' transformer still gets hot, it's not the CCFLs or leads.

3. Swap the transformers. If the 'Hot' transformer gets hot in the new position, it is bad. If it doesn't, you have eliminated the transformer.

4. Swap the driver ICs. Again, does the problem follow the IC, or not.

Someone had a similar problem about a year ago. I don't recall if we ever were able to resolve the problem.

Of everything I've lost as I got old, I miss my mind the most.

We prefer working with pictures of YOUR board. That way we can spot potential causes.

PlainBill

[alexanna]

Re: Gateway FPD1976w / LE1936 Inverter Madness

Switch the positions of the CCFLs[move top ones to the bottom, and bottom to top]see if the problem follows the bulbs.

[PlainBill]

Re: Gateway FPD1976w / LE1936 Inverter Madness

I just noticed that the lamp that the hot transformer is running is also way too hot at the ends.

That would indicate this is an 'end of life' issue of the lamp. This is one reason I discourage posting any information on bypassing inverter protection features on an open forum.

PlainBill

[boomer9999]

Re: Gateway FPD1976w / LE1936 Inverter Madness

Switch the positions of the CCFLs[move top ones to the bottom, and bottom to top]see if the problem follows the bulbs.

I swapped the position of the lamp leads and the problem remains exactly the same. Guess the bulbs are ok.

Ohm'ed the transformer primary and secondaries. 2.8 ohms on both legs to common on both transformer primaries. 618 ohms on both secondaries. Cannot detect any problem on transformer with resistance measurements.

Pictures coming soon.

[alexanna]

Re: Gateway FPD1976w / LE1936 Inverter Madness

^
I'll leave this to the engineering Guys/Gals.
I have started to run into transistor problems where something is being held on to long, and causing what I think is causing the circuit to draw excessive amperage.

[smason]

Re: Gateway FPD1976w / LE1936 Inverter Madness

I swapped the position of the lamp leads and the problem remains exactly the same. Guess the bulbs are ok.

Ohm'ed the transformer primary and secondaries. 2.8 ohms on both legs to common on both transformer primaries. 618 ohms on both secondaries. Cannot detect any problem on transformer with resistance measurements.

Pictures coming soon.

I would have bet real money on a transformer with shorted turns.

When you swapped lamp leads, you swapped both bottoms for both tops?
And the same transformer got warm?

Dumb question, did you check solder joints on the transformers and related components?

[boomer9999]

Re: Gateway FPD1976w / LE1936 Inverter Madness

I would have bet real money on a transformer with shorted turns.

When you swapped lamp leads, you swapped both bottoms for both tops?
And the same transformer got warm?

Dumb question, did you check solder joints on the transformers and related components?

I swapped both sets of leads and the transformer still was hot. All joints were soldered on caps, transformer and everything else that didn't look right. Solder generally looked good all over.

Here come the pictures...

It sure looks to me like the drive on the hot transformer has way too much spikes. What could cause this?

I'll wait for some comments before I translate the location of the transformers first. Then translate the location of the mosfets to see if I can isolate any component.



My workzone:


backside of power/inverter board:


and


frontside of power/inverter board:


drive signal to cool transformer:


drive signal to hot transformer:

drive signal to mosfets from pwm on cool transformer:

drive signal to mosfets from pwm on hot transformer:


12v DC rail:

capacitive couple on output of hot transformer to lamp:

capacitive couple on output of cool transformer to lamp:

[retiredcaps]

Re: Gateway FPD1976w / LE1936 Inverter Madness

Here come the pictures...

Good job on the pictures and troubleshooting so far, but in the future, please attach your pictures using the manage attachment function here and please do not post inline for the following reasons listed at

https://www.badcaps.net/forum/showpo...5&postcount=12

Thank you.

[alexanna]

Re: Gateway FPD1976w / LE1936 Inverter Madness

Hi,

I'm new here. Working on my first LCD repair!!

OK, it is opened up on the bench. Power on the display, the lamps in the panel power up for about 1 sec. then turn off, then turn on for about 1 sec. then remain off. The blue led power button remains on. (display from PC is working correctly and is visible with flashlight when inverter is down)

All caps look fine on the outside. Scoped the DC and everything is smooth.

I tacked a 1 meg resistor from vsense on pwm to ground to keep the inverter running. 1 of the 2 inverter transformers gets very hot and the waveforms on the mosfet drive have huge 100 volt spikes on the leading edge of both half of the primary side of inverter. The other transformer has clean signals. Bringing the scope near the HV traces shows the hot transformer is got the same output as the cool one - a nice sinewave.

This is the board I'm dealing with:
https://www.badcaps.net/forum/attach...1&d=1303052623

I have tried replacing one cap at a time with the spares I have and there is no change.

Help

My experience of working with a scope has been automotive, and yes there were more things to look at besides secondary ignition.
In using a scope I have found it very important to know what type of pattern I was looking at, and what a good pattern looks like.
You are lucky to have a scope available to you.
My suggestion would be to look at the good side of the inverter and see what a normal pattern looks like, and then look at the bad side.
You can easily swap a component side to side of the inverter and see which component causes the pattern to change sides.

[boomer9999]

Re: Gateway FPD1976w / LE1936 Inverter Madness

I would have bet real money on a transformer with shorted turns.

When you swapped lamp leads, you swapped both bottoms for both tops?
And the same transformer got warm?

Dumb question, did you check solder joints on the transformers and related components?

In my own stupidity -by not taking the time to label with CCFL leads I reversed them after flipping the power board over on the bench. Now with the 4 connectors seated properly, I am getting correct waveforms on all 4 inverter primaries and no more hot transformer or lamps. Still would not stay on.

Traced the problem to a noisy line on the v-sense to the pwm. Tracing the circuit shows an RC filter on that line. In an effort to calm down the line, I added an extra RC filter, similar to the smd components already in place. (I did not remove the orig.) The extra RC removed about 1/2 of the ripple on that line, but not the average DC volts which read a steady 1V before and after.

She is now working - I will not say fixed until after a week or so of 8 hour days. Exciting really..the first computer panel I have worked on.

I did fix a samsung 46 inch lcd TV before. That thing toasted it's pwm controller and burnt up it's power FET. First time smd soldering on that too. Replaced PWM and FET and still working 3 months now.

I have a dim Dell in the trunk. It's next.

[PlainBill]

Re: Gateway FPD1976w / LE1936 Inverter Madness

In my own stupidity -by not taking the time to label with CCFL leads I reversed them after flipping the power board over on the bench. Now with the 4 connectors seated properly, I am getting correct waveforms on all 4 inverter primaries and no more hot transformer or lamps. Still would not stay on.

Traced the problem to a noisy line on the v-sense to the pwm. Tracing the circuit shows an RC filter on that line. In an effort to calm down the line, I added an extra RC filter, similar to the smd components already in place. (I did not remove the orig.) The extra RC removed about 1/2 of the ripple on that line, but not the average DC volts which read a steady 1V before and after.

She is now working - I will not say fixed until after a week or so of 8 hour days. Exciting really..the first computer panel I have worked on.

I did fix a samsung 46 inch lcd TV before. That thing toasted it's pwm controller and burnt up it's power FET. First time smd soldering on that too. Replaced PWM and FET and still working 3 months now.

I have a dim Dell in the trunk. It's next.

Heck of a job, give yourself a big pat on the back.

It sounds like you're on a roll.

PlainBill

[none314]

Re: Gateway FPD1976w / LE1936 Inverter Madness

Hello,

I am new to these forums and new to LCD monitor repair. I am experiencing the same issue where my Gateway LE1936 will turn on for one second, off one second, on one second, and then finally off. I have replaced all the capacitors on the power board to no avail. As a last-ditch effort, I purchased a brand-new replacement power supply board from Singapore; and it is still exhibiting the same symptoms. Do you think it could be something related to the backlight CCFL lamps? Are these replaceable? If so, how do you disassemble the the LCD screen itself with this particular model? Any help would be GREATLY appreciated.

Kind Regards,

-Mark B.

[killian6pk]

Re: Gateway FPD1976w / LE1936 Inverter Madness

Since your monitor might be a different revision than this thread, you should start a new thread and include pictures of the top and bottom of the power board and the top of the vga/dvi board. Check the sticky on how to take pictures and post them. Someone will help you. In the mean time start making a list of your caps with UF and Volts along with height in mm. You will probably need to replace them.

Also do you have a multimeter and soldering iron? Do you know how to use them?