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

[rddube]

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

Ok, so I took voltage readings on the MP10091 with all 3 resistors in place:

Pin 1: 5.54V
Pin 2: 0.136V
Pin 3: 0.136V
Pin 4: 0.092V
Pin 5: 0.0V
Pin 6: 1.207V
Pin 7: 3.58V
Pin 8: 3.91V
Pin 9: 5.54V
Pin 10: 0.0V
Pin 11: 0.0V
Pin 12: 5.88V
Pin 13: 13.3V
Pin 14: 13.01V
Pin 15: 15.22V
Pin 16: 15.19V

[Dumah Brazorf]

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

I think you read the right side top/bottom instead of bottom/top.
If R804 is dropping 5V it should passing ~0,5A so 2,5W. It should be hot.

[rddube]

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

I think you read the right side top/bottom instead of bottom/top.
If R804 is dropping 5V it should passing ~0,5A so 2,5W. It should be hot.

You're quite right Dumah, my error. Should look like this, sorry for the error:

Pin 1: 5.54V
Pin 2: 0.136V
Pin 3: 0.136V
Pin 4: 0.092V
Pin 5: 0.0V
Pin 6: 1.207V
Pin 7: 3.58V
Pin 8: 3.91V

Pin 16: 5.54V
Pin 15: 0.0V
Pin 14: 0.0V
Pin 13: 5.88V
Pin 12: 13.3V
Pin 11: 13.01V
Pin 10: 15.22V
Pin 9: 15.19V

[Dumah Brazorf]

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

Maybe you should use a 10k resistor for the white connection.
Check resistance of your lamps leads and on the blue high voltage caps.

[will62]

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

Can you flip your meter over to AC and remeasure pins 1,2,3 & 16?

[rddube]

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

Maybe you should use a 10k resistor for the white connection.
Check resistance of your lamps leads and on the blue high voltage caps.

Ok, checked the resistance on the lamp leads and I get for both 0L. Also, c831 and C834 give me 0L and C817 gives me 449ohms.

[rddube]

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

Can you flip your meter over to AC and remeasure pins 1,2,3 & 16?

Switching my meter to AC gives me the following:

Pin 1: 15.4mv dropping
Pin 2: 5.5mv dropping
Pin 3: 15.2mv dropping
Pin 16: 21.6mv dropping

[rddube]

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

Will62: You asked me if I have an oscilloscope in another thread, and yes I do. It is a very basic one JYE Tech DSO138 (those small chinese Oscilloscopes that come in a kit) but it works!

[will62]

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

OK, chip appears shut down. I'm adding another pic with the voltages you measured. About this time, I'd be looking for gate pwm signal with the oscope.
But you won't see it if chip is down. Let's see what Budm recommends.

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

[budm]

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

I would put the scope pin on the GATE drive pin and keep it there then power up the board and you should see the drive signal, if the drive signals are present for both GATE that means the inveter transformer primary will get the drive Voltage and will try to fire up the lamp if that does not happen then to protection will kick in, or if it detects over current when the MOSFET are driven, the protection also kicks in, this will happen very fast. the circuit will have to try to drive the lamps first if there is problem (I.E lamp do not conduct) within set time then protection will kick in.
The typical protection circuit used in the CCFL will shutdown the circuit:
1) It will detect if the lamp will conduct current and stay conduction when the Firing Voltage is applied to the lamps, if the lamps do not conduct then the shutdown occur. The detection circuit detect the error on the lamp return side of each lamp, so one bad lamp will shutdown the circuit. Some circuit may try to fire up the lamps up to three times.
2) if the lamps are not connected then it will detect no lamp current flow due to no load connected so you do not want to have over 1000V at the lamp connector present without load otherwise it will start arcing to the near by circuit.
3) Over current will also shutdown the circuit.
Some circuit may have 3 seconds timer, if the false is present during the first 3 seconds then the circuit is shutdown, thus 3 seconds to black, everything has to be working within 3 seconds for the circuit to stay on.
The MP1009 looks to have only 300mSec.

[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.

[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

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??

[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

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

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

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?

[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

[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

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.