Benq FP91G+ Monitor

[matthmal]

Hi Guys,

I have a Benq FP91G+ Monitor which every now and then sort of freaks out.

When I bought this monitor it had a fault which was 2 seconds to black so I followed the post of retiredcaps and found 2 bad C5707 transistors. When replacing the bad transistors it started to work good for 2 days but it started to freak out.

Sometimes I try to turn it on and doesn't turn on. Sometimes the power button turns on and remains on with no display and if you try to turn the button off it remains on.

Sometimes it just works fine and sometimes even 2 seconds to black.

None of the transistors have a reading less than 50 ohms so they don't appear to be faulty.

Please find attached photos of the back of the monitor, the power board (front and back) and also the video board (front and back).

Any suggestions guys?

[budm]

Re: Benq FP91G+ Monitor

Did you resolder all the connections on the inverter transformer, transistors in the inverter section.
Look for small rings around the joints.
http://s807.photobucket.com/user/bud...?sort=3&page=1
Also check the resistance of the PF801 to make sure it is less than 1 Ohm.

[matthmal]

Re: Benq FP91G+ Monitor

Did you resolder all the connections on the inverter transformer, transistors in the inverter section.
Look for small rings around the joints.
http://s807.photobucket.com/user/bud...?sort=3&page=1
Also check the resistance of the PF801 to make sure it is less than 1 Ohm.

Yes everything is resoldered including the transistors.

The PF801 is giving the reading 000 both ways when connected on the board. Is that fine or should I remove one leg from the board?

[Lumberjack777]

Re: Benq FP91G+ Monitor

That's a pico fuse and should have resistance of 1 ohm or so. Now if that 000 means out of range, then the fuse is open. You can also use the diode checker and it should give a very low number. Like 1 or so.

[matthmal]

Re: Benq FP91G+ Monitor

I don't have a diode tester. how can I check it with a normal meter? On my meter 1 means out of range.

[budm]

Re: Benq FP91G+ Monitor

In Ohm mode, touch the two probes together and see what you get (it will show the probe's leads resistance), the fuse should show about the same reading.

[matthmal]

Re: Benq FP91G+ Monitor

I got the same reading when touching the probes together...000

[budm]

Re: Benq FP91G+ Monitor

That fuse is OK.
"Sometimes I try to turn it on and doesn't turn on. Sometimes the power button turns on and remains on with no display and if you try to turn the button off it remains on." That seems like the main/logic board is not responding correctly. I see 3-pin voltage regulator, you should take the DC reading of all 3 pin (the middle pin is connected internally to the big tab on top) when it is working and when it is not working.

[matthmal]

Re: Benq FP91G+ Monitor

will do so and will let you know.

[Davi.p]

Re: Benq FP91G+ Monitor

Budm, i respect you but every time that i come here i read a message of you and i ask myself why don't you buy the key with the letter "?"

[bomcla]

Re: Benq FP91G+ Monitor

check thes mosfet in the inverter FU9024N e c5707 ! and 'success that face to the white screen to monitor. controls the condensers 0.22 between the C5707.

[budm]

Re: Benq FP91G+ Monitor

"Budm, i respect you but every time that i come here i read a message of you and i ask myself why don't you buy the key with the letter "?"
Is it that important? Sometime I am up real late trying to look at all those pictures, drawing out the diagram and answer the questions, too worn out to look at my typing, Sorry if that bother you too much.
So lets get back to the subject of this thread.

[Davi.p]

Re: Benq FP91G+ Monitor

Budm, for you and for native english people maybe not, but for me it's more difficult to read, however yes, other people are much more difficult to understand.

[budm]

Re: Benq FP91G+ Monitor

I will try to do better.

[matthmal]

Re: Benq FP91G+ Monitor

check thes mosfet in the inverter FU9024N e c5707 ! and 'success that face to the white screen to monitor. controls the condensers 0.22 between the C5707.

sorry for the late reply. was a bit busy lately. Will check the mosfet and will get back with an answer

[matthmal]

Re: Benq FP91G+ Monitor

That fuse is OK.
"Sometimes I try to turn it on and doesn't turn on. Sometimes the power button turns on and remains on with no display and if you try to turn the button off it remains on." That seems like the main/logic board is not responding correctly. I see 3-pin voltage regulator, you should take the DC reading of all 3 pin (the middle pin is connected internally to the big tab on top) when it is working and when it is not working.

i noticed a small crack on the solder of one of the C5707s that I replaced so I resoldered it. I will keep it 2 days for testing and if it fails again I will do your test buddy and will post the results.

[retiredcaps]

Re: Benq FP91G+ Monitor

Budm, for you and for native english people maybe not, but for me it's more difficult to read, however yes, other people are much more difficult to understand.

Seriously?

You are going to give someone who spends a lot of time helping people with clear well written posts grief over a question mark?????

[matthmal]

Re: Benq FP91G+ Monitor

That fuse is OK.
"Sometimes I try to turn it on and doesn't turn on. Sometimes the power button turns on and remains on with no display and if you try to turn the button off it remains on." That seems like the main/logic board is not responding correctly. I see 3-pin voltage regulator, you should take the DC reading of all 3 pin (the middle pin is connected internally to the big tab on top) when it is working and when it is not working.

After re-soldering the C5707 transistors, I now have a new symptom. The monitor works for a while and then turns off. I switch it on again and works for a couple of minutes or hours and shuts down again.

I tested the 3 pin voltage regulator and got the below results:
Pin 1 -> 3.3V
Pin 2 -> 1.8V
Pin 3 -> 0.00V

I still need to test the regulator when the monitor fails though as I tested it while it was on and working.

[budm]

Re: Benq FP91G+ Monitor

Service manual, not sure if it matches your boards or not.

[matthmal]

Re: Benq FP91G+ Monitor

Service manual, not sure if it matches your boards or not.

They don't seem to match as my PCB P/N is: 48.L1J02.A02

Please correct me if I'm wrong