Benq monitor rarely turns on

[paulmars]

beng fp91g+ (q9t4) monitor. Mostly wont turn on. Once in awhile it does and works fine. However, that's very seldom. The on off switch hot side is 3.3vdc. The switch grounds that when its pressed and my dvm then reads 0vdc. Every time. Ive traced it to the display circuit board plug, gray wire. So, it goes from 3.3vdc to 0vdc when the switch is pressed - Every time. Over and over I can do this and every once in awhile, the unit powers up and it works fine. however, the next time, it wont power up.

Any ideas what could be wrong? All the caps look fine. Ive also inspected all solder joints.

tks,
pa

[selldoor]

Re: Benq monitor rarely turns on

Found that hairdryer yet you need to find it again- try heating the power supply caps.
Welcome to the forum-
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back (in the same orientation) and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed

https://www.badcaps.net/forum/attach...7&d=1280167246

https://www.badcaps.net/forum/attach...6&d=1280167246

https://www.badcaps.net/forum/attach...4&d=1280167246



Please can you update your profile with country and mains voltage

[paulmars]

Re: Benq monitor rarely turns on

Pictures attached.

took ele troubleshooting 20 years ago. Have basic DVM and a soldering iron.

usa 115vac

[selldoor]

Re: Benq monitor rarely turns on

Yes it is usually solder joints with benq boards - whilst the top of the board pic is good the back could do with being a bit sharper. What is the white deposit on the 16/20? legged device.

I was serious about the hairdrier.

Can you test the voltage on the main cap- HIGH Voltage so care.
Meter on vDC600 one probe on each leg.
It should have a voltage before you press the on button.
Should be 325vDC

No just spotted you put country and voltage in the script - its a lot better if its in the profile
Voltage should be 170vdc

[paulmars]

Re: Benq monitor rarely turns on

I took 4 pics back of each board, 2 w/flash, 2 w/o and posted the best. I could try again. White stuff? 16/20 legs? On front of pwr board white adhesive holding 100 ufd 450v cap to board. On other board white line on top of IC. Dont know why. cant feel it or wipe it off.

no hairdryer, but might be able borrow one. After heat the caps then what?

Going to ck cap voltage now. If I dont post again...well....

[paulmars]

Re: Benq monitor rarely turns on

162vdc

[paulmars]

Re: Benq monitor rarely turns on

i entered info in profile. please confirm it struck for me. tks

[selldoor]

Re: Benq monitor rarely turns on

This what I meant - perhaps I got wrong board -may be just dust

[paulmars]

Re: Benq monitor rarely turns on

oh that. Several of the ICs on bottom side PCB look like that. I think they were made that way. Rough surface.

[selldoor]

Re: Benq monitor rarely turns on

Hmm they are usually quite smooth
Voltage is a little low but depends on your mains. Next test would be on the connector form the power supply board to the main board. Meter on VDC 20 Black probe on a ground screw test each pin with the red probe. Do it fitrst when just plugged in and again after you press the on button.
With the hairdrier you are gently warming the caps on the power supply then trying to switch on - if that doesnt make any difference try the few caps on the main.

[selldoor]

Re: Benq monitor rarely turns on

What happens if instead of using the on button you ground the grey pin on the
connector. Can you trace from that pin - looks like it is going to go via a resistor? to the
biggish square chip? Also what is that black mark about halfway down that chip, almost opposite pin 4?

[paulmars]

Re: Benq monitor rarely turns on

selldoor, "and again after you press the on button." Press and release, or press and hold while testing?

"What happens if instead of using the on button you ground the grey pin on the
connector." Electrically, that's the same thing, right? I did put my probe there the other day and it goes ground when the switch is closed.

"Can you trace from that pin - looks like it is going to go via a resistor? to the
biggish square chip?" I looked both sides of PCB, and I cant tell where it goes.

I see no black mark.

[paulmars]

Re: Benq monitor rarely turns on

pins white to black:
3.3vdc
no pin
3.3
5.0
5.0
0
0
0
0
0
0

press pwr switch and she powered up. With green LED, voltages the same, except the last one (black) went from zero to 1.86vdc, when LED went orange all the points were the same, except that last black one again, it went to 3.3

now each and every press of the button, the LED changes. I dont except this to last. Well, maybe until I put the case back together.

[paulmars]

Re: Benq monitor rarely turns on

its been on for hours in stand by mode. Every few hours I turn it off, then back on. It goes green, then after some seconds goes orange. A few times Ive left it off for over an hour and it again turns on fine.

THEN, just now I turned if off to put it away and its staying orange. It wont turn off. I check the voltage and it goes from 3.3 to zero when i press the switch, but still it stays on.

HELP!

[selldoor]

Re: Benq monitor rarely turns on

I just hate intermittant problems

selldoor, "and again after you press the on button." Press and release, or press and hold while testing?

As the pins do not appear to be labeled I just meant press and release then test.
If we know which is the PSON pin then yes test that whilst press ing the on off button

"What happens if instead of using the on button you ground the grey pin on the connector." Electrically, that's the same thing, right? I did put my probe there the other day and it goes ground when the switch is closed.

Yes they should be but as this is an intermittant problem I was trying to cut out the switch completely to eliminate it.

"Can you trace from that pin - looks like it is going to go via a resistor? to the
biggish square chip?" I looked both sides of PCB, and I cant tell where it goes.

I see no black mark.

I will add apic in a few mins

[paulmars]

Re: Benq monitor rarely turns on

yellow and red lines? yes that the R it goes to. I cant trace where it goes after that. this is a multi layer board, maybe.

now it wont turn on again.

[selldoor]

Re: Benq monitor rarely turns on

The red arrow points to the black spot?

[paulmars]

Re: Benq monitor rarely turns on

I see it now. A little almost perfectly round black dot. I dont know what/why its there. Ill try the hair dryer thing shortly, if that is still relevant.

[paulmars]

Re: Benq monitor rarely turns on

When on, the switch wont turn it off. When off, the switch wont turn it on. The switch sometimes works, after pushing it over and over.

Any more ideas or should i scrap the monitor?

p

[martyparish]

Re: Benq monitor rarely turns on

Don't scrap it, try the original suggestion. [hair dryer on caps]

If it works fine some of the time, then it's going to be a cheap fix most likely, just have to figure it out.

If it were me, I'd just take the leap, and replace those caps. You're only talking about ~$10.