Question about BenQ FP71G 17" LCD Monitor

2 Answers

BenQ FP71G+ power supply problem

This may sound like a silly question, but how do you tell which electronic components may be faulty? Also, how do you tell which components are which?

Would an assumption that every component that leaked out white "goo" should be replaced first? There are three components on a circuit board that appear to have leaked something out. One is black, cylidrical, and about 4cm long. Side reads PW(M)105C (C)0516. The others are blue, about the size of an aspirin tablet, and read SEC 222M SE 220V~X1 Y1 400V~C.

If there is another thread that I should refer to for help that would be appreciated as well.

Posted by on

  • 20 more comments 
  • hltemp01 Apr 08, 2008

    Thanks Mark...



    The problem is exactly as you described it... power light on the front is on, the monitor can detect whether it is receiving a signal (i.e. light changes from orange to green) and the LCT panel itself is working properly (i.e. if I shine a light into it I can see the image that is displayed).



    Any suggestions on how to diagnose the problem :)... I am trying to do it myself, largely as a learning exercise.



    Visually, all of the capacitors look OK (i.e. they are not burst and there is nothing leaking out). There are slight discolorations on the circuit board (not sure if these are indications of overheating). One seems to be placed in an area where I cannot figure out what would have been the source of heat (half way between what looks like a transformer (?) and something labeled "L801".



    The second is between something labelled L702, a resistor, and a capacitor. Having said that, on the other side of the circuit board, there is something labeled IC701.



    Regarding the labeling of components... am I right in interpreting:

    R = resistor

    C = capacitor

    D = diode

    L = ?

    T = ?

    Q = ?

  • hltemp01 Apr 09, 2008

    Thanks Mark... now my ignorance will really come through :)...



    I have a multimeter (that is the good part)... operating one... that may be a different question. When you are talking about testing for continuity, is that essentially testing the resistance of the circuit and making sure it is greater than 0?



    Also, for a transistor, how do I check it to see if it is shorted?

  • hltemp01 Apr 09, 2008

    Two more questions... I did some reading :)...



    Do I need to take the transistors off the board to test them?



    Is this simply a question of making sure that the power flows from one of the lead on the transistor through to the other two but not in any of the other four directions? (if that makes sense)

  • hltemp01 Apr 09, 2008

    Maybe I have the only multimeter out there that does not make noises :). It does not have a speaker either (although it does have something for testing transistors (hFE?) but that would require me to remove the transistor off the board.



    My assumption is that a conductivity test is the same setting as would be used for testing for resistance (i.e. ohms). Conveniently, one of the settings on the dial has a diode symbol beside it ( -|>- ) so I tried this.



    The following is what I get as resistances. What is confusing me a little, though, is the following... if there is another problem (i.e. short) on the circuit board, might I not be just reading the resistance through a different path on the circuit?



    Transistor 1:

    pin 1 to 2 - 652

    pin 1 to 3 - 652

    pin 2 to 1 - 1582

    pin 2 to 3 - 1286

    pin 3 to 1 - 1890

    pin 3 to 2 - 145



    Transistor 2:

    pin 1 to 2 - 651

    pin 1 to 3 - 651

    pin 2 to 1 - 1581

    pin 2 to 3 - 1283

    pin 3 to 1 - 1889

    pin 3 to 2 - 145



    Transistor 3:

    pin 1 to 2 - 135

    pin 1 to 3 - 3

    pin 2 to 1 - 196

    pin 2 to 3 - 194

    pin 3 to 1 - 2

    pin 3 to 2 - 133



    Transistor 4:

    pin 1 to 2 - 135

    pin 1 to 3 - 2

    pin 2 to 1 - 196

    pin 2 to 3 - 194

    pin 3 to 1 - 3

    pin 3 to 2 - 132

  • hltemp01 Apr 09, 2008

    On my current meter 0 = free flow of current (i.e. open) 1 = no flow of current (i.e. closed).



    The fuse itself lets current through for about 1/2 seconds (the resistance is around 100ohm) and then blocks off the current. This repeats after a few minutes (i.e. it resets itself, and when I apply current blocks it off after about 1/2 second)



    Should I assume the fuse is dodgy.



    As an aside, is item #4 in your lise desolder?

  • hltemp01 Apr 10, 2008

    The diode near the top of the circuit board (D801) seems dead. The resistance is almost the same in both directions (approx 130 Ohm). The diode near the middle of the circuit board (D803) seems ok as the resistance in one direction is almost 10x the one in the other direction (145 Ohm in one direction and approx 1300 Ohm in the other).



    Now, regarding the diodes... any surface markings appear to have faded away a long, long time ago :). Any way of deciphering which way the one to replace should go? Also, any suggestions on the specs for the diode?



    On the slow blow ceramic fuse... any suggestions on the type (my guess is that there are different ratings, but I could be wrong on this one).



    As an aside, there is one other component on the back of the board that appears to have generated a significant amount of heat over time. It is labelled IC701. Any idea what this is and could it also be causing problems?

  • hltemp01 Apr 10, 2008

    Hmmhh... would the fact that I am in north america (and the local voltage is 110V) affect the amp rating on the fuse? or would this be taken care of by the circuit board?

  • hltemp01 Apr 10, 2008

    Thanks Mark... and good suggestion to take the photo.



    Now I will just have to track down the components :)... I will let you know how it all works out.

  • hltemp01 Apr 12, 2008

    Mark... I am having a bit of trouble finding the diodes. Any suggestions on a way to find out what the specs on the existing ones are?

  • hltemp01 May 08, 2008

    Mark... long time no hear... The parts just arrived today. Unfortunately, I am still somewhat stumped.



    After replacing the 4 transistors and the fuse the screen still stays blank. The diodes seem to work (after I took out the transistors and tested them, they were letting the current through only one way... I have a feeling that the faulty reading earlier was simply the current finding another way through the circuit) so I have not yet replaced them. Mainly the reason is that I have had not luck finding surface mounted diodes.



    Any suggestions on what to try next?



    As an aside, all of the transistors now read approximately what transistor # 2 read before (see above)... if I take them out and re-measure them, then no current flows from pin 3 to pin 2.

  • hltemp01 May 08, 2008

    Mark... long time no hear... the parts finally arrived and I tried fixing the monitor. Unfortunately, no luck.



    I replaced the 4 transistors and the fuse. The diodes seemed to work after I took out the transistors (my guess is that a fault in one of the transistors opened a circut which made it look like the diodes were blown).



    All four transistors now read the same as Transistor 1 and 2 did before (I removed one of them and tested the path from pin 3 to pin 2 when disconnected... no current flows through).



    Any thoughts / suggestions?

  • hltemp01 May 09, 2008

    The other two transistors do not seem to be blown...



    1 -> 2 600

    1 -> 3 800

    2 -> 1 1600 (flips to no current after about 1 sec)

    2 -> 3 no current

    3 -> 1 800

    3 -> 2 1900



    You will probably think I am silly at this point, but (for testing), I now replaced PF801 by a solid piece of wire... no change.

  • hltemp01 May 10, 2008

    Mark... I am sorry, but I am not sure that I understand the last post... coud you walk me through it a bit more slowly?



    How would I check 3.3v from pin 1 of the logic board connection to the power board?

  • hltemp01 May 13, 2008

    Mark... I am not sure if my earlier message made it through... how would I go about checking the voltage from pin 1 of the logic board connection to the power board (the CCFLs were plugged into the connectors)?

  • hltemp01 May 20, 2008

    Mark... sorry for asking repetetive questions... but just a few items to clarify:



    1) for measuring voltage, what should I use as the second point (ground?)



    2) how do I check for the flow of voltage across the fused link... given it is a hard connection, wouldn't the voltage difference between the two sides of it be 0V?



    Thanks

  • hltemp01 May 20, 2008

    Thanks for the quick response... I don't seem to be getting almost any voltage on the pin #1 (hopefully I am testing the correct pin)... Essentially, it is pin marked #1 on the connector from the power/inverter board to the logic board. The voltage on this pin is VERY low (i.e. <0.1 volt). This was measured when the power light was green.

  • hltemp01 May 24, 2008

    OK... on Pin #2 I do have voltage (I thought I had checked that originally, but it seems like I messed it up). The voltage seems to be 3.15V though... it does not seem to reach 3.3v that you mentioned.

  • hltemp01 May 24, 2008

    As a side note... the above measurement was made with the inverter/power board placed in the monitor, the logic board connected to the power board, and the logic board hooked up to the panel (i.e. everything connected up as if the monitor was live).



    Also as a, potentially, silly question. There are four connectors from the bulbs to the inverter board. Two have white/pink cables and two have black/blue cables. Is there anything specific about those cables? Right now, the pink/white are connected to CN801 and CN803 and the blue/black are connected to CN802 and CN804.

  • hltemp01 May 30, 2008

    Mark... have not heard from you in a while :)... any suggestions on next steps?

  • hltemp01 May 31, 2008

    Thanks Mark... The other problem that I am starting to find is that this thread is getting long :).



    I should have warned you earlier that I have no fear of electricity :)... As an aside... all of the tests below were done without the panel being connected (i.e. circuit boards powered up, hooked up to the CCFLs, hooked up to a computer sending a video signal, monitor turned on with the light green).



    1) the voltage on both sides of the PF is 19.82V. This is true on the connection points of the PF as well as on other elements that are connected by the circuit board to those connection points (not sure if this description makes sense)



    2) For the 4SC 5707s:

    - the voltage on the bottom and the middle pin is 0.2V

    - the voltage on the top pin is 0V

    - (top, middle and bottom are references looking at the circuit board with teh power cable sticking out towards me)



    3) the voltage on both sides of the diodes is 0.2V



    4) There are two things that look like transistors with large heat sink attached to them close to the PF (D701 and D702). They have voltages of 19.82V and 5.4V on the middle pin. No voltage on any of the other pins.



    5) On the solder connection... I had thought about that too. Unfortunately, I had not good way of checking my soldering (some of it does look ugly) so what I did was to check for continuity between the pins on the transistors and other elements close by on the circuit board that should be connected to them. This worked in all cases (although admittedly I don't know how the current that is put out by my volt meter compares to what is normally flowing through them).



    As an aside... is there any chance that I put in one of the diodes back in the wrong direction (I took one out for testing and replaced it). Both the one I took out and the one that I did not touch are letting the current flow through in the same direction.



    The 4 2SC5707s are reading the following resistances:

    - pin 1 to pin 2 - 645 ohm

    - pin 1 to pin 3 - 645 ohm

    - pin 2 to pin 1 - 1575 ohm

    - pin 2 to pin 3 - 1230 ohm

    - pin 3 to pin 1 - 1870 ohm

    - pin 3 to pin 2 - 145 ohm

    (pin numbers from top to bottom with power cable sticking out towards me)



    Diodes are reading 145 ohm in one direction and approx 1230 in the other.



    The two FUx transistors seem to be OK in that none of the paths read as 0 resistance.

  • hltemp01 Jun 06, 2008

    Mark... I finally had some signs of life, but then it died again in a glorious fashion :)



    I tried to resolder all of the connections that I had played with originally (i.e. the 4 2SC5707's and the two diodes). After this, the monitor turned on and stayed on for about 30-40 seconds. I was all ready to celebrate when smoke started coming from the back side.



    Itended up burning out two of the components:



    1) one of the FUXXX transistors (the number on the board is Q805).



    2) one of the 2SC5705's (this one took longer to burn out... it did not actually start smoking until I re-plugged in the monitor board side up (the first time it started smoking it was board side down because I was looking at the screen).



    Any thoughts on what may have gone wrong. I have a few more 2SC5707's which I could plug in but I do not have replacement Fuxx's at this time.

  • hltemp01 Jun 06, 2008

    As an aside... if I plug in the monitor (with the burned-out FUXX missing and the burned out 2SC5707 missing) it turns on for about 3-4 seconds displaying the image)

×

2 Answers

  • Level 1:

    An expert who has achieved level 1.

  • Contributor
  • 1 Answer

I checked all what is explained here but, first, all the components are ok, then my problem is a little bit different from this.
My monitor (Benq FP71G+) turns on perfectly but after about 1 hour or less the LCD panel turns off (so backlight and signal, if I check with a light spotted on to the LCD panel I don't see anything) but power LED is green.
If I turn off and then on it turns on again but the brightness start to dim and then the screen go off.
If leave it off for about two minutes (but sometimes for a couple of seconds!!) then it works again for another hour (or less...).
I thinked to change capacitors (not SMD).
What do You think?
Thank You

Posted on Jul 14, 2009

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points

    All-Star:

    An expert that got 10 achievements.

    MVP:

    An expert that got 5 achievements.

    Vice President:

    An expert whose answer got voted for 100 times.

  • Master
  • 472 Answers

The white goo you refer too is actually glue =)

If you could let me know a little more about what your screen is/is not doing then I can help further.

I will assume you have a power light on the front, but no picture.
If so, then you have a failed inverter circuit. This will require someone with a mild technical knowledge to diagnose and repair.
Hope that helps =)

Posted on Apr 08, 2008

  • 21 more comments 
  • Peter Thompson
    Peter Thompson Apr 09, 2008

    Well you are on your way, so lets give it a little nugde =)



    If you are familiar with multimeters, then this is going to be a walk in the park, at least some of it will be.



    Set your multimeter to test for continuity, (it will make a sound when the 2 probes are held together to show they are shorting out..normally a small speaker looking icon.) and over on the far edge where the CCFL tubes connect to the board you will see 4 small transformers (that is your T by the way).



    Near those are 2 pairs of black transistors with 3 legs on them, 2 up the top area, and 2 down in the bottom. They are marked with a Qxxx near them. Number on them will be either C5707 or C5706.



    Check those to see if any have been shorted. If one of each pair is shorted, then replace both in that pair regardless.



    We shall start with that and then let me know how you get on before phase 2 begins. I will do it like this deliberatly because many people who find and replace what is in phase 1, end up doing the same repair over and over without considering there may have been a reason something died in the first place.

  • Peter Thompson
    Peter Thompson Apr 09, 2008

    Ok, For an initial test there is no need to remove them. Make sure the multimeter is working and in the right mode. It is the only setting that will give a tone when the 2 probes are touched together.

    Put one probe on the centre pin, and touch the other on either of the 2 outside pins, do both outside pins like this.

    You really need to check between all combinations, and with only 3 pins it gets pretty obvious. Also make sure to check the 2 outside pins against each other, so no middle pin, just one probe onto each outer pin.



    If you touch 2 of the pins and you get the tone from the multimeter, then that is shorted. It dosn't matter if only one of the 2 are shorted since you need to replace them as a pair anyway.



    Do the same for all 4 of those transistors. Sometimes, and it is rare they havn't shorted "yet", but we will cover that soon.

  • Peter Thompson
    Peter Thompson Apr 09, 2008

    Correct you are, at this time, Transistor 3&4 are very suspect with the really low numbers. The transistor failure is so obvious using a meter with a tone, there is no need to remove them.

    You will really need a digital multimeter if you want to get this done correctly. Once someone finds out you fixed one..that's the end of your spare time anyway =)



    Now onto phase 2.



    You will see a marking on the board PF801

    PF=Poly Fuse (sneaky arn't they) We need that to register 0 for a period of time. If you hold the probes on there for a second as you would normally, then you will miss this one.

    It cuts out after a few seconds unlike a normal fuse that goes almost instantly. The other thing about these fuses is they reset themselves.

    We need to test if the current can flow through this fuse for a period of say 10 seconds.

    Problem with your current meter is without a tone, it maybe saying 0 but meaning it is open, blown.

    If you suspect this, then you need to get something to make a loop with a light and battery to show it has power constantly flowing through it.

    This fuse while you have it opened should be replaced by a ceramic slow blow fuse anyway. The original is dodgy at best.



    Phase 3 will be dependant on the result of phase 2, but involves yet more testing on a few other components. Still transistor pair 3&4 are the current suspects.



    I will also add a note here for anyone considering this about the inherent dangers of what lives inside LCD's.

    As well as this, in your tool arsenal you should have..


    • A digital multimeter - With continuity tone

    • Good soldering Iron, prefereably temperature controlled.

    • Solder (well naturally)

    • A solder ****** - Desoldering braid is ok, but it's messy.

    • A pair of fine tweezers (borrow the wifes..she will love you for it)

    Although all this seems to take awhile, on average I can have a monitor apart, tested in all areas, transistors, fuse and a few other bits replaced if need be and back together running on the desk in around 10-15 minutes. It just takes a bit of practice.

  • Peter Thompson
    Peter Thompson Apr 09, 2008

    LOL, censorship at it's finest =)

    its a solder s.u.c.k.e.r

    OK yes the fuse is done and should be replaced at any chance with the one I mentioned, slow blow ceramic.



    It's just a good idea to always check that fuse as part of the diagnostics to see if it has played any part in the events. Sometimes it is just that fuse that drops out.



    Next up phase 3:

    You will see on the back of the board there are 2 large black surface mount diodes. One at the top, the other around the middle of the board.

    To check those put your probes onto each end of it (does not matter which way around) and get a reading from it. Swap ends with the probe and check the reading again.

    What we want here is for one end to be high, and the other end to be half the high reading. A very low number is ok, as long as it's only from one end. If you get a low number at both ends, replace it. Also use the same principal as you did with the transistors. Compare the results from one with the results from the other.

    Remove the 2 dead transistors (or in this case suspect since we cannot be 100% certain) and recheck the diodes again. Somtimes they can give a false positive with the transistors still in place, but the first test should always have in in still.

    This helps to see if the diode itself was a part of the problem. They do get very hot during use and are prone to dying.



    So summary:


    • Check all 4 transistors for shorts using DMM (digital multimeter)

    • Compare values between the 4 of them (as pairs)

    • Check for shorts on the PF, replace with slow blow ceramic fuse

    • Check values of 2 main diodes under the board

    • Compare values of both as well, then recheck after transistors are removed.

    • Take careful notes of the orientation of any component you need to replace. Transistors must go back in the same direction they came out and same goes for the diodes. (there is a thin white stripe on one end of the diodes.) Even if possible take a photo of the area you will be working in so you can refer back if needed.

    That is just about it. Finding the parts can be a headache but the transistors are (full number) 2SC5707 or in some cases 2SC5706 and made by Sanyo

    There are a few other issues that can happen, but in 99% of cases this will get you through.


  • Peter Thompson
    Peter Thompson Apr 10, 2008

    I will have to drag out the schematics to get exact specs for the diodes, though I have used any other I could find around the same size before without issues.

    The white stripe on the diode should be facing towards the transistors you have been checking.

    The fuse should be rated to 2amps (they are just about all 250volts)

    The IC701 is a voltage regulator and they often work under extreme heat. They are normally mounted onto heatsinks for this reason. This version of the monitor uses a surface mount instead so the PCB absorbs the excess heat and dissipates it like a heatsink would, so you can end up with a patch like you describe.


  • Peter Thompson
    Peter Thompson Apr 10, 2008

    The voltage differences are taken care of in the primary circuit. After that it is all the same.

    The bridge rectifier sorts out the AC-DC conversion and is very early in the primary stage.

    It is the large IC sticking up about 2" from the power plug with 4 pins and a tapered end.



    So

  • Peter Thompson
    Peter Thompson Apr 10, 2008

    The voltage differences are taken care of in the primary circuit. After that it is all the same.

    The bridge rectifier sorts out the AC-DC conversion and is very early in the primary stage.

    It is the large IC sticking up about 2" from the power plug with 4 pins and a tapered end.



    So if

  • Peter Thompson
    Peter Thompson Apr 10, 2008

    The voltage differences are taken care of in the primary circuit. After that it is all the same.

    The bridge rectifier sorts out the AC-DC conversion and is very early in the primary stage.

    It is the large IC sticking up about 2" from the power plug with 4 pins and a tapered end.



    So if you only

  • Peter Thompson
    Peter Thompson Apr 10, 2008

    The voltage differences are taken care of in the primary circuit. After that it is all the same.

    The bridge rectifier sorts out the AC-DC conversion and is very early in the primary stage.

    It is the large IC sticking up about 2" from the power plug with 4 pins and a tapered end.



    So if you

  • Peter Thompson
    Peter Thompson Apr 10, 2008

    The voltage differences are taken care of in the primary circuit. After that it is all the same.

    The bridge rectifier sorts out the AC-DC conversion and is very early in the primary stage.

    It is the large IC sticking up about 2" from the power plug with 4 pins and a tapered end.



    So if you only have

  • Peter Thompson
    Peter Thompson Apr 10, 2008

    The voltage differences are taken care of in the primary circuit. After that it is all the same.

    The bridge rectifier sorts out the AC-DC conversion and is very early in the primary stage.

    It is the large IC sticking up about 2" from the power plug with 4 pins and a tapered end.



    So if you only have 110v

  • Peter Thompson
    Peter Thompson Apr 10, 2008

    The voltage differences are taken care of in the primary circuit. After that it is all the same.

    The bridge rectifier sorts out the AC-DC conversion and is very early in the primary stage.

    It is the large IC sticking up about 2" from the power plug with 4 pins and a tapered end.



    So if you only have 110v 2amp

  • Peter Thompson
    Peter Thompson Apr 10, 2008

    The fuse won't make a difference between 110v or 240v, just as long as it's 2amp.



    By the time the power hits this section of the board it's all the same no matter where you live.

  • Peter Thompson
    Peter Thompson Apr 10, 2008

    Oh almost forgot one last thing. Try and find a half decent magnifying glass to check the solder after you have done it to check for solder spatter etc. Also use the metre to check them as well to check for shorts between the 3 pads on each after you get them back in. It only takes a blip of contact between two of the legs and your back at square one.



    Since your in the USA, there is a company there called Bluestar I believe that stocks the transistors.



    Good luck =)

  • Peter Thompson
    Peter Thompson Apr 12, 2008

    The only schematic I have here for the BenQ series has the standard diodes not surface mount.

    The link to the part is HERE so it would just be a case of getting that but in a surface mount form.

    The original is a schottky barrier diode rated to 60v 3amps.

  • Peter Thompson
    Peter Thompson Apr 12, 2008

    The only schematic I have here for the BenQ series has the standard diodes not surface mount.

    The link to the part is HERE so it would just be a case of getting that but in a surface mount form.

    The original is a schottky barrier diode rated to 60v 3amps. The

  • Peter Thompson
    Peter Thompson May 09, 2008

    There are 2 other transistors (actually Fets) on the board, again, one for each side of the inverter circuit that should also be checked. They can be various part numbers, but normally begin with FU29xxxx.



    After that, make sure to check that fuse fully. Apply power to the board, keep well clear of the primay power side and avoid touching anything other then to check the polyfuse is allowing power into the circuit. It should be marked as either PF801. That can read good, but still be bad.

    It is about halfway between the primary transformer and the top of the board.

  • Peter Thompson
    Peter Thompson May 09, 2008

    I should have mentioned that you will need to have the CCFL's plugged into the connectors to get any voltage to the inverter section. If there are no CCFL's or a fault in the circuit, the protection kicks in and removes power rather quickly.

    Easiest way is to put the screen face down on a towel on a flat surface, then plug the connectors into the board. There is no need at this point to worry about hooking up the cable from the logic board to the panel, BUT it will only come on for a few seconds anyway since there si no video comming into the monitor. You can of course hook a PC upto it to make sure it dosn't go into sleep mode.

    I keep a spare set of CCFLs for this purpose..saves a lot of messing around.

    Failing that check you have 3.3v from pin 1 of the logic boards connection to the power board. This should read 3.3volts when the power light on the monitir is green and 0v when amber. That is the trigger point to turn the inverter on.

  • Peter Thompson
    Peter Thompson May 13, 2008

    OK, open up the monitor so the screen is laying face down on a towel. Put the power/inverter assembly next to it in side the chassis. Connect the CCFLs to the inverter connectors.

    Connect the front panel connector to the logic board so we can see whats happeneing with the power light. So you will end up with the monitor completely open, but connected excluding the cable from the logic board to the panel.



    Apply power to the monitor. Keep clear of the whole powerboard and move across to the inverter.



    Pin 1 will be the outside top pin of the connector between the inverter board and the logic board. When the monitor is on, the voltage should read 3.3v. When the power light is orange, the monitor is turned off or the video card changes resoloutions, then this will read 0v.

    The +3.3v signal tells the inverter to turn the CCFLs on or off etc.



    The other thing while you have it like this is to check that voltage is indeed flowing across the fused link (PF801)

  • Peter Thompson
    Peter Thompson May 20, 2008

    Heh, sorry I forgot you bridged the fuse with a solid link. I guess you can rule that out =)



    And yes, use the metal chassis for the ground connection for the multimeter. Just ensure the power inverter board is screwed into the chassis as it would normally be so you are getting ground across all areas of the board.

  • Peter Thompson
    Peter Thompson May 20, 2008

    Check pin 2 also (top next to pin 1) It may have been setup backwards. BenQ have a habit of changing whatever suits their mood that day.

  • Peter Thompson
    Peter Thompson May 30, 2008

    Sorry, email servers here at not the best lately. Only way to know if anyone has responded half the time is to look back at the thread..as you can imagine, I have several hundred threads =)

    Ok, back to the problem at hand..

    The voltage seems fine, it normally outputs 3.2v, but anywhere in that zone is fine. It just sends a signal out to the inverter circuit to turn on.

    The tubes have no real particular place, they all recieve the same voltage. There are 2 seperate tubes at the top and bottom, so each connector goes to an individual tube is all.

    Remove the panel completely, cover the high volatage section so you do not fry yourself and proceed as follows.


    1. Turn the monitor on while it is connected to a running computer. (need this to give constant power on to the inverter circuit)

    2. Place the ground lead of your multimeter (MM) into the chassis.

    3. Using only the red lead, check the voltage of each side of the fuse (PF)

    4. Check the voltage where the PF connects to the IC directly off the fuses trace. It is a 14 pin IC that controls the backlights and also contains the protection circuitry to shut it down should it need too.

    5. Check the transistors (the 4 2SC5707's and the 2 FUXXX) for shorts again. They can go instantly bad if there is a secondary fault. Also double check those 2 main diodes there.



    Sometimes just because something is soldered into the slot, does not mean it has full and correct contact back to the board.

  • Peter Thompson
    Peter Thompson May 31, 2008

    Yes it is getting a bit on the long side =)

    Anyway.. The diodes have a white mark on one end. That should be closest to the CCFL connector edge.

    The transistors, looking from the component side of the board should have their back (the metal tag) on the same side as the heavier line on the board.

    Can you send me a photo of both sides of the board and I will look over it to see if I can see anything wrong from here.

    emailto:saitek@tpg.com.au (save you hunting through the pages hehe)

×

Add Your Answer

Uploading: 0%

my-video-file.mp4

Complete. Click "Add" to insert your video. Add

×

Loading...
Loading...

Related Questions:

1 Answer

Q7T4-fp71g BENQ monitor picture come and go.power on.thanks.


try it in another coputer if not work you need mantinace eng

Mar 25, 2011 | BenQ FP71G 17" LCD Monitor

1 Answer

Where can I buy a logic PCB for FP71G Benq


Shenzhen VIIV Technology Co., Ltd is an expert at PCB,PCBA and Rigid Borad manufacturer based in shenzhen China.


MSN:viivtech@msn.cn

Yahoo: viivtechavril

SKYPE: viivtech

Mobile: 86)15989403359

Email:avril@szviivtech.com ,zhwei930@163.com

Website :www.szviivtech.com

Tel: 0086 755-29477736

Fax: 0086 755-29410695

ADD: sha

Jul 13, 2010 | BenQ FP71G 17" LCD Monitor

1 Answer

I have a BenQ FP71G+ monitor and the auto adjust message pops up frequently and the screen adjusts itself.


radioactivet, A qualified technician will need to investigate the units "switch-mode-power-supply" for typical "faults" and locate the faulty (bad) component(s) that ma be causing monitor to act this way. "Noise" on the +5 volt DC rail going to the vga/lcd interface (processor) may be why display is acting "strange" with uncalled for pop-up's appearing!! That's the very first place I would investigate when dealing with ANY COLD-CATHODE-FLUORESCENT-LAMP, BACK-LIT LCD DISPLAY. 12fixlouie

May 31, 2010 | BenQ FP71G 17" LCD Monitor

1 Answer

Benq 567s lcd monitor does not power up. Switch led blinks but goes dead. Tried replacing capacitor 450v 82uf with 400v 100 uf but did not work. please help.


That cap is for the Primary power supply switching circuits. How is the DC secondary side, no blown fuse, shorted transistors in the inverter circuits? Pictures will help, budmrtn@aol.com
http://s807.photobucket.com/home/budm/allalbums
http://en.wikipedia.org/wiki/Capacitor_plague
http://www.badcaps.net
It may have the same bd as DELL since BenQ makes monitors for DELL and HP.

May 21, 2010 | BenQ FP71G 17" LCD Monitor

1 Answer

I have a BenQ FP71G+ 17 lcd monitor


When you have strange problem like this, first place to look will be the power supply section. Look for burnt parts, leaking/bulging caps, that will be the starting point.
http://s807.photobucket.com/home/budm/allalbums
http://en.wikipedia.org/wiki/Capacitor_plague

May 20, 2010 | BenQ FP71G 17" LCD Monitor

1 Answer

What happens when lcd monitor shows for about 2 seconds then blacks out?


A few possibilities, starting with the most likely: - The backlight tube (CCFL) - The inverter that produces the high voltage for the tube - The main power supply which provides the voltage for the inverter
The backlight may be user replaceable using some care and a few tools for access, including a soldering iron. The inverter is often a small board that is plugged into the both the main power supply and the lamp itself. Both of these parts may be available from sources other than BenQ (if that is the make you have) since they probably buy them rather than make them.
To avoid replacing things that ain't broke, it would help if you owned a simple digital multimeter which can be found at auto parts stores or electronic supply houses. This would allow you to eliminate items that are working as they should.

Feb 20, 2010 | BenQ FP71G 17" LCD Monitor

1 Answer

Lcd monitor BenQ fp71g screen doesnt come on when i hit the power button you can hear a click sound and the green power light comes on but then goes off modelq7t4


Hello

Parts (probably capacitors) in the monitor power supply are failing. My company repairs these for an average of $50.00 + parts + shipping or take it to a local repairman.

Jul 28, 2009 | Computer Monitors

2 Answers

Benq screen shuts down when pc is plugged in


If it's a 71g and not 71g+ resolder transistors 2sc5707 on invertor board along with grey condensers and inverter transformer.This should solve the problem if it was display shutting off with power led remaining on.Otherwise check power section.

Feb 24, 2008 | BenQ FP71G 17" LCD Monitor

Not finding what you are looking for?
BenQ FP71G 17" LCD Monitor Logo

5,822 people viewed this question

Ask a Question

Usually answered in minutes!

Top BenQ Computer Monitors Experts

Tony

Level 3 Expert

2598 Answers

Matthew Spark
Matthew Spark

Level 3 Expert

1042 Answers

Donald DCruz
Donald DCruz

Level 3 Expert

17129 Answers

Are you a BenQ Computer Monitor Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides

Loading...