Benq G2255 doesn't power on - amber power light when plugged in

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Hello Dumah,

Thank you for your reply. What do you mean by checking the power button? If eeprom issue, how can I fix it?

I did plug in the power board and main board only, and the amber light comes on. Checked the voltages on the voltage regulator at top of photo 5 of my second post with photos, and I get 3.3V on left leg, and 1.8V on right leg, so that looks ok.

Then I checked the 2 caps on that same board, removed them and they test ok. Resistance at cap legs when installed and removed is 85ohms...does that look normal?

Many thanks for your input!

The 80 ohms does sound low. Above, you mentioned that the caps measured 85 ohms when removed. That sounds way too low for a good cap. You might want to remove those again and recheck resistance (3V to gnd).

Also, please check the area on the back of the board, circled in the pic. Looks like something scraped across the board there.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Hello gentlemen,

There was a delay in the Digikey shipment so only tomorrow or the next day.

Started looking at my problem on the main board, and when I measure 3.3V to ground I get 80 ohms. That sounds a bit low, don' t you think. If it is too low, probably what is giving me that amber power switch light when I plug in the monitor. Any ideas what I should be looking at?

I inspected the main board but can't find any physical trace of anything. What do you think?

Photos attached to this post for convenience.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Ordered the parts from Digikey and should be getting them today - incredible 1 day delivery service from Digikey! Will report back once the new Mosfet is installed and the Caps changed. Hope this fixes that issue, and if so, will have to start thinking about the other issue of the mainboard.....

[Dumah Brazorf]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Wrote something silly then edited out.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Uhoh, ok i'm tired.

Dumah, not sure what you mean?

[Dumah Brazorf]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Uhoh, ok i'm tired.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

It is C817 - I took it out and measured resistance, there is no resistance. Value I get with my fluke multimeter is 32nf and with my multi transistor tester is 17pf.

I have these other high voltage caps from a Dell monitor scrap board and they are written:
5C
3kv

What do you think?

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Yes, looks like the closest Digikey has is 10pf. For the discolored blue one, what is the cap number on the board? I believe 2 of those are used to monitor over voltage.

Also, I mentioned in a previous post that I was concerned about the TG gate driver being on when the chip is down. I was able to find some info on how some of these driver chips function. I don't think you have a problem there, which is good news.

"When the oscillator is in the off state, the low side MOSFET (Q2) is always conducting due to the IC internal logic. This creates a path for the resonance between the DC blocking capacitor and the transformer primary leakage inductance, which introduces some undesirable noise in the lamp off state."

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

The one I find suspect is blue and written:
8
3KV
SEC
Not sure what I should get as I don't see 8pf 3KV capacitors on digikey? By the way, that one is blue but has a yellow tint to it as if it overheated slightly. Anything else I could get if I can't get the exact value?

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Rddube, you're going to pay the $8 minimum shipping, so you might as well try to get everything in one go. On the through hole caps, pull one leg off of the pcb and check them. 475 ohms sounds low. See what it measures out of circuit. If any doubt, go ahead and get them in this order.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

I plan on changing the Caps on this board, so will be ordering a set of caps. Is there anything else I should get like the blue cap that measures 475ohm, would that be a cap to change? Is there any caps related to the Mosfet that should be changed?

Tks.

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

I would get 3.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

This one is pretty close. You can get 3pcs. for ~$7 (non-rohs?). (shipping would take about 2-3 weeks)

https://www.ebay.com/itm/3PCS-AP9962...oAAOSwLVZVj0~5

As far as the 13V on pin 11 (Top gate drive), can you lift pin 4 on the mosfet so we can see if the 13V is coming from inside the driver chip or from the mosfet?

On similar circuits, pin 12 (SW, 13.3V) connects to source2, drain1 and the transformer primary. I know we should have voltage on source2, but I don't think that we can get voltage on gate2 without a short.

If you decide to continue on the project, you could try one of the 30V mosfets, just so you could move on in the troubleshooting.


This mosfet could work as well. It is $0.86 + shipping:
https://www.mouser.com/productdetail...Gz3mDeSA%3D%3D

Will62, Mouser charge 20$ to ship to Canada. Do you think this could be good, as Digi-Key charge 8$ shipping. How many should I get, considering that there is something else which blows the Mosfet?
https://www.digikey.ca/product-detai...6-1-ND/4862961

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

So I decided to take the plunge and change that AP9962 for the 30V version AF4910N, and guess what!

Well first after doing the switch of Mosfets, I plugged everything back main board, CFL connectors, etc. and plugged in the monitor - amber light just like when I started. Then I remembered Budm saying I probably have 2 problems, i.e. mainboard and power board.

So I did the 3 resistor setup without main board, plugged to the CFL's and bingo, they turned on for about 2-3 seconds and went out. I unplugged the powerboard, waited a few seconds, plugged in and CFL'S came on and stayed on for approximately 10 seconds. I unplugged the power waited again another 5-10 seconds, plugged it in again and this time nothing - zilch. I did the test 3 or 4 times and they wouldn't come on again.

So I unplugged everything, kept the resistors in and went and took voltage measurements on the chip and got exactly the same results as before from pin 1 to 16 - exactly.

When I changed the Mosfet and before applying power, I got approx 475K ohms between S1 and D1 and approx 370K between S2 and D2. Now after the test and everything I get 1.2 mega ohms between S1 and D1 and about the same thing between S2 and D2.

What do you think?

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

I would go back to post#70 and do what Budm recommended. While you've got everything set up, go ahead and look at the pic in post #65. Check the waves on OV1,2 & LI1,2. Check voltage ripple as well. As Budm mentioned, shutdown will happen quickly, so you need to start each test from power off, caps drained.


Some other notes:
1. Based on the 13V not coming from gate, and your previous mosfet checks, that mosfet may be OK.
2. We have a pin-out of the MP10091ES, but no datasheet. I've been going back to the MP1009 datasheet, hoping that the pin specs are similar. They may not be.
3. If chip is shut down, I'd expect both gate drive pins to be 0V. I may be wrong here, need someone else to chime in.
4. The datasheet for Mp1009 shows that the max pwm voltage on pin 8 (dbrt) is 2V. Right now we have 3.9V jumped to that wire. Is that causing a problem? May be different for MP10091ES.

Hope you don't quit, it's just starting to get interesting.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Ok, so I did lift pin 4 from the mosfet and still get 13V on pin 11, so it's coming from the driver chip.

So what do you think a next step could be, change the mosfet for the 30V one?

[will62]

Re: Benq G2255 doesn't power on - amber power light when plugged in

This one is pretty close. You can get 3pcs. for ~$7 (non-rohs?). (shipping would take about 2-3 weeks)

https://www.ebay.com/itm/3PCS-AP9962...oAAOSwLVZVj0~5

As far as the 13V on pin 11 (Top gate drive), can you lift pin 4 on the mosfet so we can see if the 13V is coming from inside the driver chip or from the mosfet?

On similar circuits, pin 12 (SW, 13.3V) connects to source2, drain1 and the transformer primary. I know we should have voltage on source2, but I don't think that we can get voltage on gate2 without a short.

If you decide to continue on the project, you could try one of the 30V mosfets, just so you could move on in the troubleshooting.


This mosfet could work as well. It is $0.86 + shipping:
https://www.mouser.com/productdetail...Gz3mDeSA%3D%3D

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Q808 is 2 mosfets in 1 package.
The circuit alter readings indeed.

If I remove AP9962AGM and it is not good, I haven't been able to find any of those chips on the net, seems they don't sell them anymore??

[Dumah Brazorf]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Q808 is 2 mosfets in 1 package.
The circuit alter readings indeed.

[rddube]

Re: Benq G2255 doesn't power on - amber power light when plugged in

Hello gentlemen,

I have to admit that at this point, I feel a little confused although I understand your explanation Budm, I think this is getting beyond my skills for repair.

We are trying to get the inverter working, but I also have a problem with the logic board, so down the end, it might not be economically viable to repair this monitor? What do you think?

Also, there seems to be 2 gates but only one Mosfet and one inverter transformer?

One oddity: Both gate drives should be 0V if chip is down. You have 0V on BG (bottom), But 13V on TG (top).

Budm, you didn't comment on this quote? Is this normal?

On the mosfet, I measured again between S1 and D1 and get 475K, on S2 and D2 I get 47K?? Should I be measuring it out of circuit? On that topic I succeeded in removing a AF4910N from the other board. When I measure S1 and D1, I get mega ohms resistance, same from S2 to D2.