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Repairing BenQ 17″ LCD Monitor
By Jestine Yong on January 31, 2008
I came across a common fault problem in BenQ 17″ LCD Monitor. The problem is have power but no display. Once you has opened the LCD cover, check the pico fuse for open circuit (very common), the push pull transistors C5707 for short circuit and the Buck royer circuit p-channel fet FQU11P06 also for short circuit too. For your information, if you can’t get the FQU11p06 you can always use FU9024N as a replacement. Resolder all the high voltage transformer pins and replace the components above and I’m sure you will bring back the life of this BenQ 17″ LCD Monitor.
You may go to this fairchild semiconductor website to download the spec of the FQU11P06 P-channel FET.
http://www.fairchildsemi.com/ds/FQ/FQU11P06.pdf
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Frank Aquino
June 1, 2010 at 11:45 am
Dear Jestine, I notice the dates on this site are quite old, so you may not be active these days, but if you are I would appreciate any help you can offer. I have a Benq FP71E+ with an intermittent fault. When booting up the computer, the screen momentarily appears but the top half of the screen is darker. This lasts about 1/2 of a second, then the whole screen goes black. The blue switch lamp remains blue. Repeated presssing on and off makes no difference. When off, a hard "thump" of the screen onto the desk will often cause it to illuminate correctly after it is switch on again. Sometimes thumping the upper bezel achieves the same thing. This suggested to me that a solder connection or a plug was at fault, but I have resoldered everything I can, without achieving any improvement. All the capacitors have bright flat shiny tops, and nothing else looks overheated or damaged. I disassembled the screen part as far as I dared without actually exposing the CCFLs. While disassembling I noticed the wires to the lamps were crimped severely around plastic clips to hold them in place. I wondered if this could be a failure mode, so I left the wires unclipped when I reassembled it, and the problem arreared to be solved. Unfortunately the fault has returned. Assuming there are no hidden faulty solder joints, can you deduce why a thump would restore it to working order, albeit temporarily?
admin
June 2, 2010 at 8:14 pm
Hi Frank,
I'm still active writing in this blog. You may click on the "Home" at the right side under Blogroll and it will takes you to the latest post of the day. In your case , yes it could the wire problem. For LCD Monitor, we have the top and bottom lamp. If the top lamp connection loose, the top display will become darker and then the whole LCD will shutdown. Why it shutdown? because the feedback circuit in the inverter board did not get the appropriate signal from the top lamps.
Sometimes the e-cap can looks good but fail when test it with ESR meter.
Jestine
John
June 7, 2010 at 11:46 pm
Hi everybody!
I have a pretty strange situation here that i'm trying to understand. My "project" is a 15" DELL monitor , model E156FPb which has this issue, picture for about a second and then the display turns off but the power LED stays ON. I aimed a flashlight to the screen in a certain angle and i could see the shapes on the desktop (icons). Ok....no big deal here, i replaced all the capacitors in the inverter and , just to be sure, the C5707 and FU9024N transistors. I re-soldered all the suspect points and double-checked the wiring and connections. It all looks good. I thought maybe it's the lamps. They can go bad right? Well, it happened that i wanted to see what voltage i have on the connectors for the lamps and that's when it happened! While holding the probes on one of the connectors, i turned the monitor on and it stayed on! With a nice clear picture too... As soon as i take the probes off, the monitor turns off. Now, i know that this has something to do with the voltage provided by the multimeter but i don't quite understand what is going on here. If you guys have more experience and know more about this, maybe you can give me a hand here. I'd really like to solve this "mystery". Thank you in advance and have a great day.
admin
June 8, 2010 at 4:26 am
HI John,
The feedback circuit shutdown the inverter if it detect bad/weak lamp. Since the meter could provide a small voltage thus this may overall did not trigger the feedback circuit and the lcd monitor would not shutdown.
Jestine
John
June 9, 2010 at 12:38 am
Thank you for answering Jestine. So, could you say that the problem is caused by one of the lamps? I'm thinking that, since they work fine (as long as the meter is connected), the lamps should be in good shape. If it's not the lamps, than what else could cause this behavior?
admin
June 9, 2010 at 8:35 am
HI John,
Chances is very high in one of the lamp.Try replace the lamp and see how it goes.
Jestine
John
June 10, 2010 at 3:14 pm
You were right. It was one of the lamps....Thank you for your help 🙂
luis
June 12, 2010 at 10:30 pm
Hi Jestine, very helpful blog
I have a BENQ FP71G monitor, after read your instrction I replaced the transistor SC5707 (4) and the two fets, plus the 1000 micros capacitos and the tunnig capacitors also, The transistor were open as well one fet, however the monitor still doesnt work.
when I turn it on I can see the benq logo quickly and then nothing.
I already tried in two different computers and the problem is the same.
I didnt replace the PF801 as I measure the voltage and looks it is working.. Any suggest please..
I resolder also all the high voltage section and the area where I can see there is a hot components..
Thank you
admin
June 13, 2010 at 8:46 am
HI Luis,
Try replace the backlight and retest. Compare the resistance of the top and the bottom high voltage transformer too.
Jestine
cp singh
June 22, 2010 at 7:51 am
smps circuit diagram with pcb layout for samsung tft lcd 17" monitor is urgently required please.
admin
June 22, 2010 at 9:03 am
H Cp Singh,
Sorry i do not carry schematic diagram.
Jestine
Simone
June 22, 2010 at 10:30 am
Dear admin, i've 4 monitor hp 1710 with benq board, the backlight go off after 3/4 seconds but the board haven't a c5707 transistor, same problem with qbell 17", have you any solution?
Many thanks
admin
June 22, 2010 at 9:19 pm
Hi Simone,
If the transistor c5707 check to be okay then suspect dry joints in the high voltage transformer or even bad backlight. Make sure the inverter ic is getting a good and stable supply voltage.
Jestine
Trust
June 26, 2010 at 10:08 am
cn u help me with the equivalent number for transistor fu9024n.by the way im a fan of all yor work. thank you.
admin
June 26, 2010 at 9:29 pm
HI Trust,
Try FQU11P06
Jestine
zuan
July 6, 2010 at 12:47 am
Hi Justine
Do you sell the component? as I find it difficult to get it in my area in Ipoh.
thanks
admin
July 6, 2010 at 9:05 am
HI Zuan,
Sorry we do not sell electronic components. Try visit this website:
http://www.mobicon.com.my/
Jestine
Mellow
July 16, 2010 at 12:49 pm
Hi Jestine,
Great advice here. I have the same Benq monitor. When I power up it will show the Benq splash screen and then go black with the power light on ie not standby. I have had it come on and show graphics then will see half the screen go dim and then whole screen to black. Sometimes a power cycle will bring it back but usally within a few minutes it is black again. I have tested transistors C5707 for short circuit and the Buck royer circuit p-channel fet FQU11P06 and appear ok. The caps physically appear ok however I dont have access to an ESR to test. Is it most likley a backlight then? ie with half the screen going dim then the whole screen going black?
Thanks
Mellow
admin
July 16, 2010 at 7:57 pm
HI Mellow,
First you need to make sure all the output voltages are good and stable. Then check on the high voltage transformer and make sure that is no tiny crack (dry joints). If all check to be okay then suspect one of the back light have problem.
Jestine
Michael
July 17, 2010 at 6:27 am
Can you please help me fix my AOC725 LCD monitor. The said unit fail to power up . I check alredy the fuse and OK.
admin
July 17, 2010 at 7:37 am
HI Michael,
If there is no output voltages from the power supply then you need to check on all components in the primary side. It can be an open resistor, bad caps or even bad power IC.
Jestine
Michael
July 19, 2010 at 6:08 am
I've check the filter cap 100uf/400v i measured there a 327vdc. so i check the pwm IC sg6841 well i measured 14v at the vdd pin#7 while at the Vin pin #3 it measured 17 volts. Is it the pwm ic is bad? I read the data sheet of sg6841 and it says that pin#3 should be -.3 to 7volts. how do i know is it bad? please help. this is my email ad vp_baquial2000@yahoo.com
many thanks jestine
admin
July 19, 2010 at 10:25 am
HI Michael,
If there is no output voltages from the smps and you have check all components and found no bad component then the biggest suspect is the power IC. The best is to direct replace and retest because sometimes a power have good supply voltage input but still will not function.
Jetsine
Andy Collins
July 20, 2010 at 3:57 am
I have just repaired two Benq FP937s monitors thanks to the information on this page. As well as dead transistors I also found dry joints in both monitors on the capacitor that sits next to the push-pull transistors.
Thanks a lot!
admin
July 20, 2010 at 8:15 am
HI Andy,
You are welcome!
Jestine
gautam
July 22, 2010 at 7:14 am
i have 19″ benq lcd, when i start power on button.. signal is ok ..but after few second(2-3 second) …signal not comieng yet….
so can u help me…
admin
July 22, 2010 at 7:41 pm
Hi Gautam,
Did you get to see the display within the 2-3 seconds? What is the colour of the power LED?
jestine
Chris
July 26, 2010 at 4:57 pm
Hi hope you can help my benq q7c4 I powered up my pc and the light remains orange. So I press the light it goes off . I press again it goes green I get the logo then a caption saying no signal is detected then the light goes to orange and blk screen. Pls can you advice me on how to fix this problem ?
admin
July 27, 2010 at 8:15 am
HI CHRIS,
First you need to make sure the output voltages of SMPS are good and stable. Make sure no bulged e-caps too. If all the voltages tested good even in the mainboard then suspect a bad MCU in the mainboard.
Jestine
Tim Sando
July 28, 2010 at 6:48 am
Hi, Have a BENQ FP71G+S The screen Turns on normally for 2 seconds, then the screen turns off, but the light on the bezel stays on. i dont think that it is the backlight, but my client said that it has been doing this after a power failure, so am not sure what is wrong, is it the power board inside or the other board? i have re soldered some joints but that didnt solve the problem. there is discolouration in the pcb, and there is an electrical component underneath where the discolouration is which had like a flux type of stuff on it. any ideas?
admin
July 28, 2010 at 9:05 am
Hi Tim,
The shutdown problem can be caused by many factors like output voltages from SMPS not stable or low, bad filter caps, dry joints especially the high voltage transformer pin, bad mainboard (mostly bad MCU) and once of the backlight have problem. I suggest that if all tested good then you may need to compare the backlight. One more thing check all the components that is relate to the discoloration area.
Jestine
George
August 14, 2010 at 9:13 am
Hi, Jestine. Congratulations about your website.
I have a BenQ G2020HD 22' inch monitor. After the electricity suddenly power down the monitor won't switch on. I press the power button the green led lights on for 1 second and then it goes off. The monitor won't switch on. What could be the problem? Thanks.
admin
August 14, 2010 at 10:41 am
Hi George,
Thanks! In your case it could be the mainboard have problem. First you need to make sure is the power supply itself have problem and not the mainboard. You need to check the output voltages from the power supply to see if there is any power when the power LED light went off. If there is no power output then you need to troubleshoot the power supply area. If there is output voltages to the mainboard, most likely the mainboard have problem. For your information the power LED signal came from the mainboard.
Jestine
Ebrahim
August 26, 2010 at 1:55 pm
Hi Jetsine, great site! Anyhow, I fixed Benq t701 model q7t3 by replacing 4 - 2sc5707 and 3A Fuse. However, on high resoultion (1024 by 768) or higher the characters are broken. Any suggestion on how to fix this problem.
admin
August 26, 2010 at 7:41 pm
Hi Ebrahim,
I have not seen such problem before but if all the output voltages are good and stable then suspect problem either in the mainboard (MCU) or in the LCD panel. You may need a good working parts to swap it and retest.
Jestine
syed
August 28, 2010 at 1:42 am
hi my monitor starts auto adjusting every second plz help me out with this problem thank you
admin
August 28, 2010 at 9:19 am
Hi Syed,
It is either the EEPROM IC or the MCU program have corrupted. But both ICs with programs is hard to get from the market.
Jestine
Davor
August 31, 2010 at 2:55 am
Hi everybody!
I'm trying to fix an HP L1740 and any help would be appreciated.
The monitor goes on and off as soon as the VGA cable is plugged into the graphic card connector. It is not the backlight problem; the monitor keeps to restart itself in intervals of about 5 seconds: it turns on for a second, then goes off for four seconds, and then goes on again. Just before going off it displays the "Monitor going to sleep" message.
But, if i keep the power, menu or "+" switch pressed, the monitor stops restartig, except I do not have any control by means of the switch board, as I keep one of the buttons pressed (the on/off switch, for example).
I disconnected the switch board from the main board and now the monitor works ok, except, I do not have any control.
I tested the switches and two of them (the on/off and the "+") do not make a short when pressed, but do not have a short when depressed either...
Thank you in advance!
admin
August 31, 2010 at 9:07 am
Hi Davor,
From your description it seems like the front panel have problem but you said you have tested it. If all the supply voltages to the mainboard is good and did not fluctuate then i suspect the MCU may have fault because most of the front panel signal lines is directly connected to the MCU.
Jestine
Mukesh
September 5, 2010 at 1:56 pm
Hi Jestin
I have Benq 22" G2220HD LCD, i have just bought it and everything was fine till 15 days, then one day suddenly the menu and all other buttons(including power button) stopped working, but screen was still on and fine. so i thought of switching the main power supply on and off. when i did that the monitor never turned back on, i tried changing the power cables and all but no use. I gave it to service centre and they said that they changed the board, it worked fine for one day then again the buttons stopped working and when i turned off the main power and turned it back on...there was no power in it. Its a brand new monitor and i dont know wats causing the problem....if u have any suggestions do reply.....plz help...thanx in advance
admin
September 6, 2010 at 10:33 am
HI Mukesh,
If the power supply have good output voltages then suspect a bad Mainboard. Most probably the MCU have problem.
Jestine
Mukesh
September 14, 2010 at 4:25 am
Hi Jestine
In regard to my previous post about benq G2220HD ...the service center man came and replaced both the power board and main board. The monitor switched on but still the menu buttons were not working and also the screen was diplaying red blue green black and white in succession. I plugged a viewsonic LCD and its working fine. Plz suggest something. Thnx
admin
September 14, 2010 at 8:40 am
HI Mukesh,
If after the replacement of power and mainboard with the same problem then suspect bad lcd panel. I believe he could replace the lcd panel as well since he got the power and mainboard.
Jestine
Ray Thompson
September 16, 2010 at 7:18 pm
Thanks for the information on this FET I have a number of BenQ's and they run different numbers in different boards and I wasn't too sure if the were substitutable as the boards are different models.I know now. Thanks very much.
Ray.
admin
September 16, 2010 at 8:49 pm
HI Ray,
You are right there are few models with different part number. If it belong to the same type of component say FET then you can try to use it. Turn on the machine for a while then off it to see if the FET hot or not. If it is hot then it is not compatible and if it is warm then you can use it.
Jestine
Johan
September 23, 2010 at 10:01 am
I have the same monitor come in "dead". We repaired the monitor by replaceing the pico fuse but now we another problem. When the power plug is inserted, we have a white screen. If the signal cable is put in the monitor works fine but even when switched off, the screen stays white. Justine, have you any idea what could be wrong?
Regards
Johan
Firose
September 23, 2010 at 11:52 am
Your information good, Thankyou Mr Jestine
admin
September 23, 2010 at 8:49 pm
Hi Johan,
This could be the problem with Mainboard because it still producing an On signal to the Inverter IC thus high voltage produced and you could see the white screen. Most probably is the MCU in the mainboard have problem.
Jestine
louie
September 23, 2010 at 10:47 pm
Very informative site and thanks for helping 🙂 Can you help me with my problem with my LCD 19" HANNS, Problem is LCD seems to work as normal if not connected from a computer (Power on normally then displays a No signal when not connected, which is good) Problem is when I connect it to computer Power Button just keep flashing (green) with no display. I replaced all capacitor at PS unit(No ESR Meter - I use non-branded capacitor a replacement). Can you further help me what to look? Inverter is included on the PS unit made by SAMPO (indicated on the board).
Have a good day.. Thanks
admin
September 24, 2010 at 10:06 pm
Hi louie,
If the voltages measured good and stable in the main board and when you connected the vga cable and the power keep flashing then it could be the problem of bad MCU in the mainboard. This type of problem were quite common in Samsung model.
Jestine