Problem with LCD Panel board

[mokie]

Hello, I have a problem with a Dell 1907FPt monitor. I've already changed a couple of mosfet (AOP605) that were shorted.

But the problem now is when I plug the lcd panel conector, you can hear a sound from the psu like a little short circuit and the led in the front is blinking with no backlight and no image on the monitor.
If I unplug this board, the sound disappears and the led stays on.

This board is a M190EN04 board. There's some information on the internet about this. A pdf is also in the attachments.

I've checked voltage on power pins (+5v) and they actually drops to cero when I plug the board, so I'm looking for a blown fuse or something like that on the board.

Thanks in advance.

[stj]

Re: Problem with LCD Panel board

if it drops to zero there is a short.

if a fet shorts out and it shorts one of the main pins (S or D) to the gate pin, it often damages whatever is controlling it.

[mokie]

Re: Problem with LCD Panel board

oh god, I'm stupid. Rookie error. The conector was REVERSE!.

Now I have the monitor working but without backlight. I've checked both mosfet of the inversor and they are ok (AOP605).

I've checked the lamps with an external inverter and they are fine

[mokie]

Re: Problem with LCD Panel board

any help?

[bammbammfran]

Re: Problem with LCD Panel board

Check for dc voltage at the first corner pin of the P605 to make sure power is getting to them. Not sure if these are fused on this board since I can't see the bottom.
The pin you will be checking will probably be connected to one of the capacitors that is right next to them.
voltage may be 12-18 volts based on other boards I have seen.

if voltage is not there, check for a surface mount fuse under the board

If voltage is there, then you may have cooked the controller chip that is on the other side of the board. that chip,I think ? is an 8 pin

good bottom side picture of this area might help

[mokie]

Re: Problem with LCD Panel board

look at the picture.

On the bottom, there is an IC with 8 pins. It's a OZ9936GN

[bammbammfran]

Re: Problem with LCD Panel board

Looks like power is getting there and that no fuse was involved

That OZ9936GGN should be what sends power to the two P605
It probably sends around 5 volts to one pin to turn the P605 on
does the 5 volts show up and stay on ?

go you get 14.3 on both P605 drains ?
do the backlights flash at all ?? (leave the wide 30 pin plug that goes to the actual lcd panel disconnected when looking for a flash)

[mokie]

Re: Problem with LCD Panel board

- I don't understand well the first question, but when I turn on the monitor there isnt't any signal on the gate pin of any mosfet

- Yes, I get 14.36 volts on both drains (and both mosfets, each mosfet has 2 drains)

- The flashlight doesn't flash at all (with or without the 30 pin plug)

Probably it will be that OZ9936GN. I think this is a good deal http://www.ebay.es/itm/2X-OZ9936GN-O...-/360619504921

The problem will be the soldering though.

[bammbammfran]

Re: Problem with LCD Panel board

IF you check you old P205 and the G2 is shorted to S2 or D2, then the OZ is probably cooked

As far as soldering: For some people , removing it is a little tougher than installing one. Make sure to flux it good first then add a glob of solder to your iron tip and spread it back and forth on the S and G side while lifting slightly on the chip, you'll have less chance of trace damage this way. If that is a problem, you can cut the pins on the D side one at a time with a new exacto blade by going straight down right where the pins enter the chip then unsolder the other side

[mokie]

Re: Problem with LCD Panel board

No, actually there aren't shorted. The problem was on the N-channel. If I check between drain and source (negative and positive respectively) I got 0.5 (OK) but if I turn on the gate there's no continuity between drain and source.

Sorry for my bad explanation, I'm not english native.

[bammbammfran]

Re: Problem with LCD Panel board

OK, Your first post said shorted

It still might be an OZ controller chip issue
check pin 6 for around 5 volts in (7 is max per the datasheets)
then see if pin one gets voltage when you power it on (might be around 3 volts) should be between 2 and 4
then check 4 and 5 which should be the two pins that drive the P205
pin 7 is the dimming voltage and would depend on what the dim was set at so it may be between 0 and 3ish.

based on your picture with the pin 1 and the dot at the bottom left
pins should be as follows
8 7 6 5
1 2 3 4

[mokie]

Re: Problem with LCD Panel board

This is what I get. I guess that the OZ is cooked

[bammbammfran]

Re: Problem with LCD Panel board

It appears to be not turning on.
Hopefully that is all that it is.
Lots of work for a board that you can get in China for $18 , but hopefully someone learned something from this project.

good luck with the transplant

[mokie]

Re: Problem with LCD Panel board

ok ,thank you for all your help. I will be posting the results

[mokie]

Re: Problem with LCD Panel board

I've replaced the OZ9936 and I have the same problem, no backlight at all

[bammbammfran]

Re: Problem with LCD Panel board

did you recheck the pins to see if anything is showing up at 4 and 5 and if 1, 6 and 7 were still the same as before

[budm]

Re: Problem with LCD Panel board

So did the backlights lamps even flash for second?

[mokie]

Re: Problem with LCD Panel board

The voltages are exactly the same as before and the lamps doesn't even flash for a second.

If I light the screen, I can see the image on it.

[bammbammfran]

Re: Problem with LCD Panel board

can you post a picture of the new installed chip
just for giggles, use an ohmmeter and check pin 3 to make sure it has a good ground

[mokie]

Re: Problem with LCD Panel board

Here are photos of the new OZ9936 replaced. I did the best I could. Yes, pin 3 is connected to ground


In summary, I have checked:

- Secondary of both inverter transfomers. Around 460 ohms.
- I have desoldered all capacitors and their capacity is ok (maybe they have high ESR?)
- I have checked what I think are two fuses for the inverter zone. They are located near the OZ9936 and they are ok.
- I have replaced the two main mosfets for the inverter zone which were opened. They were P609 and I replaced them with both P605.
- I have resoldered all the connections in the high voltage zone.
- Of course I have checked both lamps with an external inverter and they are ok.

I don't know what more to do.