Hyundai L90D+ inverter mosfet problem

[Lydux]

Hi there !

I would like to thank you first for this great forum, I learn a lot here on LCD repair !

I recently found a dead 19" Hyundai L90D+ that I really would like to fix and I think I'm getting closer to this.
Here is what's the problem : just after plug in the power cord, the blue power led turns on. About 5 seconds later, this same led quickly turns to orange and everything shutdown like if a short has come (I can also hear a tick at this time). So, this process restart and loop forever. No Backlight at all.

Looking to the power/inverter board doesn't show me bulged caps, and anyway it looks like more a MOSFET issue.
I disconnected it from the logic board, the ticking stop and I get a good 12V and 5V at pins header without shutdown.

Then, I hooked SLP to 5V and the backlight starting to flash.
This drive me to the solder side of the board where I can find two dual NP mosfet (U4 and U5) named APM9932 (datasheet here ). Looking closer, I can also see a damaged smd capacitor just nearby U5 (C23). So I suspect something in that area to be the failure.

Since I cannot find service manual for this monitor, I don't really know what value is C23 nor what kind of mosfet can substitute these APM9932 (can't find them on Digikey or Mouser). And anyway, I'm not an hardcore mosfet calculator.... :p So I need your help on this point !


Am I right on what I have done ? Any advices else ?

Many thanks in advance !

[ecking767]

Re: Hyundai L90D+ inverter mosfet problem

to solve one of your problem C53 and C23 should have the same value. The circuit is symmetrical. As for the AP9932 try FairChild website cross reference

Hope this help
ecking767

[Krankshaft]

Re: Hyundai L90D+ inverter mosfet problem

Test the driver FETs with a DMM are either of them shorted?

[dondrusco]

Re: Hyundai L90D+ inverter mosfet problem

It's discharge capacitor, I think.

But exact value - I don't know. I found correct value by searching MOSFET datasheet.

https://www.badcaps.net/forum/showthread.php?t=5346

[Lydux]

Re: Hyundai L90D+ inverter mosfet problem

Test the driver FETs with a DMM are either of them shorted?

Just try this, and it seems that U4 is shorted on P channel. I've got 0v from D to S and S to D, that's it ?

Thanks to ecking767 and dondrusco for your tips guys ! I do not know this ability on Fairchild website ! Unfortunately, it doesn't return me anything with APM9932.

So, a 0.1 uF capacitor for C23 will be good ?

[themakr]

Re: Hyundai L90D+ inverter mosfet problem

Hi Lydux,

I have an identical monitor with exactly the same symptoms and am going to attempt to repair it - did you have any success with yours?

Cheers

[jetadm123]

Re: Hyundai L90D+ inverter mosfet problem

Hello! The APM9932 is available through Ebay, item 200446667412. It also looks like the seller ships worldwide. Hope this helps.

[j1979b]

Re: Hyundai L90D+ inverter mosfet problem

I too have the same problem with this board. Did you get it working by replacing the APM9932 FET's and C23 and C53 cap's?

[themakr]

Re: Hyundai L90D+ inverter mosfet problem

Just received the FETs yesterday - will give this a go in the next few days...

[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

[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.

[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.

[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?

[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.

[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

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

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

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

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 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.