Hyundai L90D+ inverter mosfet problem

[camra88]

Re: Hyundai L90D+ inverter mosfet problem

My problem is that the backlight just won't turn on. When the computer is in standby, the monitor's LED turns orange, as usual. When it gets a picture, the LED turns blue, as normal.

I have tested the both of the dual-MOSFET APM9932 packages, and the lowest resistance reading I got was ~20k ohm. According to previous posters, they "pass the test."

Next, I closely examined every capacitor I could find on both sides of the board ("FeeLux", power board) and was unable to visually identify any potentially bad capacitors.

I tested the fuse, and it is not blown.

I also do not see any burn marks on the FR-4 (neither sides).

What else could the problem be? The monitor worked this morning, then goto use it a few hours later and the backlight doesn't come on.

[jetadm123]

Re: Hyundai L90D+ inverter mosfet problem

My caps seems ok... http://kauhava.no-ip.org/pcton/hyundai/

U4
G2 -> D2 = 42 Ohm

U6
G2 -> D2 = Over 9000k keeps rising

(on-board results)
Wich one is bad?

First of all, if you posted your photos on a different site, few members will go to that site for fear of computer viruses. Please post your photos per PlainBill's links on post #26.

You provided only partial readings. I think previous members checked U4, U5 and not U6. These are duo mosfet packages. Look at the datasheet provided by retiredcaps in post #20. And you should get 6 results like post #26.

If you do not understand, PLEASE reread this entire thread.

[pcton]

Re: Hyundai L90D+ inverter mosfet problem

Textbook description of bad capacitors.
PlainBill

My caps seems ok... http://kauhava.no-ip.org/pcton/hyundai/

U4
G2 -> D2 = 42 Ohm

U6
G2 -> D2 = Over 9000k keeps rising

(on-board results)
Wich one is bad?

[PlainBill]

Re: Hyundai L90D+ inverter mosfet problem

Led goes...
100ms orange+blue led (led test?), speakers clicks
~5s blue led
sometimes 200ms orange led (for no-signal)
but then power goes off for a second
and repeat...

I might see a dim back light struggling.

Time to defuse...

Textbook description of bad capacitors.

PlainBill

[pcton]

Re: Hyundai L90D+ inverter mosfet problem

Post pictures of your boards so we can see the specifics of your board. Do not post images inline (use manage attachments) like the OP in post #1.

Describe in detail what is wrong with your lcd. Hookup a working computer to the monitor. Does the power LED come on? If you shine a flashlight, can you see the display?

Led goes...
100ms orange+blue led (led test?), speakers clicks
~5s blue led
sometimes 200ms orange led (for no-signal)
but then power goes off for a second
and repeat...

I might see a dim back light struggling.

Time to defuse...

[retiredcaps]

Re: Hyundai L90D+ inverter mosfet problem

I just got one of theese. Same problem too... no visible damage on board so far. Seems to be cummon failure. I can't fix more than bad caps without guidance tho. Standing by...

Post pictures of your boards so we can see the specifics of your board. Do not post images inline (use manage attachments) like the OP in post #1.

Describe in detail what is wrong with your lcd. Hookup a working computer to the monitor. Does the power LED come on? If you shine a flashlight, can you see the display?

[pcton]

Re: Hyundai L90D+ inverter mosfet problem

I just got one of theese. Same problem too... no visible damage on board so far. Seems to be cummon failure. I can't fix more than bad caps without guidance tho. Standing by...

[URAD_Harvey]

Re: Hyundai L90D+ inverter mosfet problem

I loved my L90D+ when it was working - so did my son and one of my clients.

Now I have 3 dead ones and want to fix 'em up.

Over the years 3 of the 4 have been sent back for warranty repair for the same problem. But now these 3 are out of warranty.

The power/inverter board is hard to find.

When I got my monitor back from repair, I noticed the brightness no longer worked correctly - soon after (within months) it failed again. I took it apart and found a dead APM9932. I remembered that one of the other monitors had an exploded ICE2AS01, blown fuse, fried 04N60C3 Mosfet and who knows what else, but it had one good APM9932. So I unsoldered it and put in on my other one. The brightness still did not function correctly, but it was usable. Again, it failed after a couple of weeks. So, this time, I wanted to really get a handle on the whole picture and I hunted all over for manuals or schematics. I found some things that were 'close' from the chip manufacturer suggested applications, but I wanted the real deal. Finally, just this week, I took the time to make a schematic. Still needs a little work on the cap values, but the finished product is so close to the manufacturer's recommended application, the caps values from that are probably close enough.

The LM358 OpAmp is used to control the Dim feature of the monitor which is done by PWM all built into the OZ960SN features (pin 14). I suspect either this section has a problem, or the DIM signal from the Processor board is faulty. I haven't got that far yet, just finished getting the schematic done so I can actually do this justice

My guess here, is that the APM9932 cannot handle the continuous load at full PWM duty cycle (full brightness) for long durations. More than likely the airflow is insufficient to cool the device under this type of load as the board is encased in a plastic protector with just a few holes which is then nestled into a confined metal casing with just a few more holes in it and all driven from convection. I think the heat is getting trapped in there and the APM9932's are paying the price with their lives. The board I have with the shorted U6 P-channel has discoloration on the opposite side for both chips from overheating the FR4. For us DIY, it may be prudent to devise some type of heat sink for these little workaholics - as long as the lamps are lit, they are switching.

=================

I had thought with that old monitor with everything fried, that perhaps I could strip everything off and play around with a clear glass LCD monitor - no inverter needed. So I took an old computer power supply and rigged it up to the Processor Board to see how much light would pass through from my desk lamp. Sadly, I discovered that the LCD matrix electronics is bad on that one, so it really took a hit when the power supply section blew up. Interestingly, the Processor Board still works . But I was able to prove (at least to myself) that the processor and LCD Matrix electronics will run off the computer supply. I did this on my other monitor that I want to fix.

I wonder if there is a way to retrofit these for LED back lighting

[retiredcaps]

Re: Hyundai L90D+ inverter mosfet problem

Finally got to sit down with the monitor. Here is what i found:
S1 - D1 > 100k
G1 - D1 > 200k
S1 - G1 > 200k

S2 - D2 = 101k
G2 - D2 = 122k
S2 - G2 = 19k

These are in-circuit results. I can pull the chip and retest it you think that would give more valid results.

Those results indicate that your FETs are good. No need to replace them or test them out of circuit.

As mentioned, i have 5 of these I'd really like to get going, so any good ideas will be greatly appreciated.

If this were me, I can see 2 approaches.

1) Since I have 5 identical monitors, I can take them all apart and try to make one good one by swapping boards, cables, lcds, panels, etc until I make a working one.

With this good one, I can then use this as a baseline for voltage measurements and something to compare to. I also have a known good working configuration.

This would make troubleshooting the other bad ones much easier.

2) Randomly pick 1 of the 5. Troubleshoot the 1 logically and methodically.

If you choose 2, post clear focused pictures AFTER reading

https://www.badcaps.net/forum/showthread.php?t=1868

Please do not post pictures inline.

Take your boards to a window on a sunny day, turn flash off, and use macro mode. Take a top down view of all your boards (front and back). Make sure the photo is legible so that we can read the PCB printing clearly. A shutter speed of 1/125 or faster will produce nice clear focus pictures. Try to get a photo that is 2000x2000 resolution or as close as possible.

Here is an example of the pictures we want.

https://www.badcaps.net/forum/showpo...94&postcount=1

[packratjohn]

Re: Hyundai L90D+ inverter mosfet problem

Finally got to sit down with the monitor. Here is what i found:
S1 - D1 > 100k
G1 - D1 > 200k
S1 - G1 > 200k

S2 - D2 = 101k
G2 - D2 = 122k
S2 - G2 = 19k

These are in-circuit results. I can pull the chip and retest it you think that would give more valid results.

This is based on the pinout for the 9932 as shown in the datasheet. As mentioned, i have 5 of these I'd really like to get going, so any good ideas will be greatly appreciated. My local electronics shop, which carries tons of parts, didn't have a cross for the 9932. I think they use NTE.

[retiredcaps]

Re: Hyundai L90D+ inverter mosfet problem

Finally got around to testing. Resistance isn't particularly low.

Post your resistance measurements and how you tested it.

Cut to the chase, what are the odds of the 9932 MOSFET solving the problem? Do i just go for it based on the experience of others?

Well if the tests show that the MOSFETs are not the problem, why replace them?

[packratjohn]

Re: Hyundai L90D+ inverter mosfet problem

Finally got around to testing. Resistance isn't particularly low. Cut to the chase, what are the odds of the 9932 MOSFET solving the problem? Do i just go for it based on the experience of others? Or is there a possibility that C23 is bad? I've worked on laptops for years, and now trying to expand to LCDs. So far had great luck, but i don't hesitate to ask the experts, either! I have 5 of these, and would like to get them going again. Thanks to all.

[retiredcaps]

Re: Hyundai L90D+ inverter mosfet problem

Just need guidance.

First, you need to find the datasheet for the MOSFET so you know the pinouts. Here it is

http://pdf1.alldatasheet.com/datashe...C/APM9932.html

Second, there is a thread re testing MOSFET

https://www.badcaps.net/forum/showth...ht=mosfet+test

Third, I like to do simple resistance test from S to G, G to D, and S to D. If these tests show low ohms (say less than 200 ohms), then I get suspicious and do further tests.

[packratjohn]

Re: Hyundai L90D+ inverter mosfet problem

No, really haven't done any component testing. Just got these in, and got one opened up to look for the obvious cap problem. I've read this site enough to know to come here first! Not familiar with MOSFET testing, haven't done much. A little direction would be great, and an idea as to what else i might expect to see. I can do board work, including SMD (to a point). Just need guidance. Thanks again

[retiredcaps]

Re: Hyundai L90D+ inverter mosfet problem

Can someone point me to the component and save my eyesight! I have the monitor cracked open.

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.

Did you try testing the MOSFETs to see if they are shorted first?

[packratjohn]

Re: Hyundai L90D+ inverter mosfet problem

I have just gotten in 5 L91Ds with the typical flashing power LED symptom. Either flashes yellow then off or yellow, blue, then off. Anyway, i wanted to try the MOSFET fix, and have found some on ebay. Can someone point me to the component and save my eyesight! I have the monitor cracked open. A pain, but easy enough i guess. Thanks in advance.

[mca16733]

Re: Hyundai L90D+ inverter mosfet problem

I replaced my APM9932 in my L90D+ with the same problem about a month ago and it worked fine...only to have it die again today. Do you guys think the op-amp (I believe it was labeled LM351) below the fried APM9932 might be causing the problem?

[themakr]

Re: Hyundai L90D+ inverter mosfet problem

Finally got around to replacing the APM9932 FET that was shorted in my monitor - put it all back together and everything is working perfectly so far - thanks to all for pointing me in the right direction.

[j1979b]

Re: Hyundai L90D+ inverter mosfet problem

Well, I went ahead and ordered the APM9332's from eBay. Installed them this evening, and the monitor is working great! The caps weren't even bad, just the FET's.

[mcfischer]

Re: Hyundai L90D+ inverter mosfet problem

I got 7 of the L91D in with one mosfet shorted. APM9932. SMD caps are all OK. judging fromm ESR readings I guess they are 1 uF or close.
Not easy to find these FETs. However, I just finished a batch of 40 IBM 9417-hb7 made by Samsung with fried mosfets and some shorted zeners.
They use SI4532DY (mouser 512-SI4532DY; $0.37 in hundred) Current rating is lower than the APM9932 but they do the same job. Customer was in a hurry so I used these in the Hyundai's. Temps are normal, all 7 have been in burn-in all day. Unless one fails day 2 burn-in I will return them to the customer day after tomorrow. This customer requests the "cheapest fix" so it is either trash them or take a chance the sub will hold up.
Mike