BENQ FP731 PF751 3A fuse Q

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • Frankenstien
    New Member
    • Aug 2009
    • 2

    #1

    BENQ FP731 PF751 3A fuse Q

    Hey all ...

    I've got one of these BENQ's that seems to have a backlight failure ...
    I have proper power button LED function but can see only a dim desktop image using a flashlight or in overhead sunlight.

    I searched 'FP731' (then 'PF751' within certain resulting found threads) and read up on the capacitor and cold solder joint issues with these displays ...
    ie. 'benq fp731 backlight problem'

    Q. does the PF751 fuse protect only the CCFL lamps, or, the entire PCB assembly? ie. would I get the dim image with a blown fuse?

    From what I've read so far, I think I'm in a little over my head, however, I would be game to crack this thing open if all it needs is a fuse.

    Also, I was unable to view any thread images earlier so don't know the fuse location, appearance or type (clip-in? / soldered?).

    Any info / advice would be appreciated ... thanks, FFF
  • Krankshaft
    Badcaps Legend
    • Jan 2007
    • 2328
    • USA

    #2
    Re: BENQ FP731 PF751 3A fuse Q

    Probably dead C5707 transistors and blown pico fuse.

    Yes the fuse only protects the inverter that drives the backlight and no replacing the fuse almost never fixes the problem.

    Replace all four C5707 transistors touch up any cracked solder joints replace the pico fuse and you should be all set.

    The pico fuse will usually have a board designation of F101 for example F stands for fuse. It won't look like a standard glass fuse it will be cylindrical probably black and will have the amperage printed on it for example 3A.
    Elements of the past and the future combining to make something not quite as good as either.

    Comment

    • Frankenstien
      New Member
      • Aug 2009
      • 2

      #3
      Re: BENQ FP731 PF751 3A fuse Q

      Thanks Krankshaft ... I shall delve into this display and see what I can see.
      From what I understand, those caps may exhibit obvious physical overheating and/or leakage ... I just need to look at a couple of images attached to threads here to get more familiar with what I'll be looking at / for.
      FFF

      Comment

      • retiredcaps
        Badcaps Legend
        • Apr 2010
        • 9271

        #4
        Re: BENQ FP731 PF751 3A fuse Q

        Just got one of these FP731 today. I checked the infamous C5707 and they test okay with the diode test.

        The PF751 fuse (3A) shows 30 ohms. I know a good fuse measures around 0.03 ohm.

        Is this considered a "good" fuse or a marginal fuse? I another Benq board and its picofuse reads 0L so I know without a doubt it is shorted.

        I'm going around checking all the other components for a shorts and checking solder joints, but would like to know if the fuse is considered good or not with a 30 ohms measurement.

        The original owner of the monitor says there is power, but no backlight, but you can see the picture faintly. It sounds like the infamous 2 seconds to black.
        --- begin sig file ---

        If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

        We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

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

        --- end sig file ---

        Comment

        • alexanna
          Member
          • Mar 2010
          • 1346

          #5
          Re: BENQ FP731 PF751 3A fuse Q

          Well I have to ask this question.What ohm reading do you get when you thouch the two leads together ? most if not all dvm meters are not going to read 0.
          also Digital meters have such high resistance built into them{ 10meg ohm} that they do not flow alot of current in the circut. It is possible to get fooled by the ohm reading,Say like having a verry slight contact that the ohm reading is good but when current flows thru the circut it opens up. The fool proof way to test would be with a load on the circut.
          Al.
          Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

          Comment

          • retiredcaps
            Badcaps Legend
            • Apr 2010
            • 9271

            #6
            Re: BENQ FP731 PF751 3A fuse Q

            Two probes together = 0.00 ohms.

            I'll put everything back together sometime later this weekend and test for secondary voltages.

            Originally posted by alexanna
            What ohm reading do you get when you thouch the two leads together ? most if not all dvm meters are not going to read 0.
            --- begin sig file ---

            If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

            We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

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

            --- end sig file ---

            Comment

            • retiredcaps
              Badcaps Legend
              • Apr 2010
              • 9271

              #7
              Re: BENQ FP731 PF751 3A fuse Q

              Scratch that. If I hold together the probes for a good 3 or 4 seconds, I get 0.03 ohms. I get 0.00 ohms if I only hold it for 1 or 2 seconds. It seems this multimeter takes a bit longer to "lock in".

              Secondary voltages all look good and solid.

              Originally posted by retiredcaps
              Two probes together = 0.00 ohms.
              Last edited by retiredcaps; 06-18-2010, 10:39 PM.
              --- begin sig file ---

              If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

              We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

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

              --- end sig file ---

              Comment

              • alexanna
                Member
                • Mar 2010
                • 1346

                #8
                Re: BENQ FP731 PF751 3A fuse Q

                Originally posted by Krankshaft
                Probably dead C5707 transistors and blown pico fuse.

                Yes the fuse only protects the inverter that drives the backlight and no replacing the fuse almost never fixes the problem.

                Replace all four C5707 transistors touch up any cracked solder joints replace the pico fuse and you should be all set.

                The pico fuse will usually have a board designation of F101 for example F stands for fuse. It won't look like a standard glass fuse it will be cylindrical probably black and will have the amperage printed on it for example 3A.
                I would like to build just a little on what Krankshaft said. I have been blessed by one of the local recycling centers here in the Midwest. I got a whole bunch or the dell H.P. Benq monitors.What I have been finding is if you can see faint image and have good power light the pico fuse is good and replacing the c5707 transistors along with Removing the inverter coils and reordering connections will most likely fix the problem. If you have no image and no power light the pico fuse is bad and there will be a couple of other transistors that will need to be replaced ,There are a couple of possibilities depending on your board I know one number is j598 but the other number escapes me at the moment, These two are more toward the middle and to one side of the board .They look just like the c5707 transistors .As far as testing these I think to get an accurate test on these you should remove them from the board, I do not think they like heat to much and they are really cheep I think you would be money ahead to just replace all six of them. After you get your monitor up and running set your computer to go into the sleep mode frequently and then wake it up many times if it is going to fail that will be the test.
                Al.
                Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                Comment

                • rivette65
                  Member
                  • May 2008
                  • 12

                  #9
                  Re: BENQ FP731 PF751 3A fuse Q

                  i have 10 Nec lc19m lcd monitors
                  the problem is that the screen goes dim after 30s .and i found that in every one there is a bad backlight bulb : that's why it goes dim i
                  i have tried to put an external bulb instead of the bad and the monitor does not go dim . and i have realise that with only one bulb the brightness of the monitor is good . so instead of changing a second new bulb i want to use only one . but the problem is the feedback circuit : with only one bulb the screen shuts down .
                  ihave you any idea about what to connect in the bulb connector on the inverter to bypass the detection of the bulb or to bypass the feedback circuit
                  thank you

                  Comment

                  • retiredcaps
                    Badcaps Legend
                    • Apr 2010
                    • 9271

                    #10
                    Re: BENQ FP731 PF751 3A fuse Q

                    Just answering my own question. I replaced the fuse today and it works. I tested all the other components before I tried the new fuse and found nothing wrong.

                    So 30 ohm for a picofuse is bad. A good fuse should be 0.3 (not 0.03 as I wrote earlier).

                    Originally posted by retiredcaps
                    The PF751 fuse (3A) shows 30 ohms. I know a good fuse measures around 0.03 ohm.

                    Is this considered a "good" fuse or a marginal fuse?
                    --- begin sig file ---

                    If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                    We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

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

                    --- end sig file ---

                    Comment

                    Related Topics

                    Collapse

                    • corrize
                      A funny fuse story – Lumix LX100 II
                      by corrize
                      Hello, I disassembled this dead camera, and found this WTF… Two fuses soldered one above the other !
                      I was pretty sure nobody touched it before, but that can't be from factory. There is flux, and capacitor is probably missing.
                      The other weird thing : the fuses are « G » fuse : (0.75A – 8V), seems very low. The original fuse should be « O » : (32V 2,5A).
                      There is « O » mark beside. All fuses have the same mark letter on main board. So, I can deduce it's a « O » fuse.
                      And this correspond to the issus I saw : when I plug the battery, I measure the voltage dropping...
                      10-19-2023, 09:58 AM
                    • jesterace
                      Samsung UE46ES8000 Blown fuse but no other signs of short
                      by jesterace
                      Hi I wonder if anyone might be able to steer me in the right direction. I have this Samsung UE46ES8000 TV and it went bang during use. The main fuse on the PSU board is open. I've checked every diode/mosfet/transistor I can see and nothing appears to be short to cause the fuse to go. The DC output of the bridge rectifier is not short either. I've seen online that some of these models are known for having their PFC mosfet or other mosfets shorting and blowing the fuse but i'm not seeing that here. If anyone aware of these models having any issues to cause this? I'm reluctant to just replace the...
                      09-11-2024, 03:14 PM
                    • jshhh
                      Help replacing fuse on my Mimaki CJV300-160 vinyl printer
                      by jshhh
                      Hi guys,

                      I'm inexperienced with electronics repairs, I've done a little bit of soldering caps and whatnot, but i have a blown fuse on this mimaki printer I got which I have bought a replacement for.

                      How do I remove this type of fuse (see picture)...it kinda looks like it would pull out of that bracket but it didn't come at first pull and I didn't want to brute force it incase it's soldered on there like most of the rest of the components.

                      Anybody know how to remove this type of fuse?

                      (The fuse is toward the bottom of the image labeled F2)...
                      06-17-2025, 01:35 AM
                    • Babbar
                      Argon SA1 audio amplifier power-supply - fuse blown after fixing the short?
                      by Babbar
                      I found a project in the electronics trash yesterday. A nice Argon SA1 audio amp with some electrical issue. Took it apart and saw that the 4A250V fuse was blown so started lifting components to find the short. Eventually got to two MOSFETs (model FTA14N50C) that are shorted and when i took them out the short was gone.

                      Now i didn't have any replacements of the same model of course but i found a couple with pretty similar spec i thought (K10A60D & K12A50D) and put them in. Also replaced the blown fuse with a 3.5A250V one. Checked another time for short circuit and plugged it in....
                      04-12-2024, 01:12 AM
                    • drykid
                      Matsui 175S microwave fuse replacement
                      by drykid
                      Hi,

                      I recently picked up a used Matsui 175S microwave that was powering up (starts, turntable rotates) but not heating. From looking online the most likely culprit was the fuse, but unfortunately in this one the fuse had heated up and fused with the (badly designed) fuse holder and couldn't be removed. I guess this might indicate further issues beyond the fuse itself but at this stage I just want to replace the fuse and see how I go from there.

                      Anyway since I couldn't get out the fuse itself the easiest fix was to replace the fuse holder assembly that runs between the...
                      12-21-2020, 01:15 PM
                    • Loading...
                    • No more items.
                    Working...