LCD 19" BENQ T905 problems

Collapse
X
 
  • Time
  • Show
Clear All
new posts

  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    Its like at first, with the green led working ok.
    Check your solder work again. Check the orientation of your caps, transistors to make sure they were installed properly.

    Your previous pictures are very hard to see (fuzzy, out of focus, and at an angle). Take a look at this picture

    https://www.badcaps.net/forum/attach...6&d=1282133540

    and compare it to yours. Our the other pic, we can see all the PCB designations CLEARLY.

    The reason I bring up the picture quality is I cannot tell from your pics where things are located.

    So I'm guessing, but on most benq boards, there are 4 C5707 transistors and 2 Fu9024 FETs.

    If you see no picture, but have a green power LED, there are 7 things to check. 1 picofuse, 4 c5707s, and 2 fu9024s. Check to make sure the picofuse is not open and the transistors and fets are not shorted.

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    So I tested it...no luck

    Didnt even show up the BenQ logo. When I plugged it, I heard a spark, but dunno if it was from inside or just the normal spark sound that sometimes is heard when you plug something.

    Its like at first, with the green led working ok.

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Ok,gonna try with that pin being dry soldered !

    Leave a comment:


  • PlainBill
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    Ok, I can solder a wire easily on the pin from the 3rd pic.
    But the pin from the 1st and 2nd pic its alone! no traces to anything
    Then you don't have to worry about it. They often use a standard bobbin; some pins are unused. You are concerned about electrical integrity, not the mechanical strength. Unless, of course, you are planning on using your monitor on an ATV.

    PlainBill

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Ok, I can solder a wire easily on the pin from the 3rd pic.
    But the pin from the 1st and 2nd pic its alone! no traces to anything

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    Maybe scratching the board a bit? What if I just leave a ball of tin? Will it be a dry joint? Maybe painting the place with a pencil? (dunno why this came to my mind)

    How about soldering the pins to another bit of the board? On the same trace,of course.
    I haven't done the scratching board so I can't say. However, I have soldered pins together when I lifted a solder pad and run a small wire from one pin to the joint. They were on the same trace.

    As you can see in this post, some people run trace wires or other hacks ...

    https://www.badcaps.net/forum/attach...5&d=1278637697

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    I used the desolder pump to desolder all the items (thought I didnt add more
    solder,never saw that technique on the videos of desoldering I have seen) and only those 2 gave problems.

    Maybe scratching the board a bit? What if I just leave a ball of tin? Will it be a dry joint? Maybe painting the place with a pencil? (dunno why this came to my mind)

    How about soldering the pins to another bit of the board? On the same trace,of course.

    I dont wanna give up yet!

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    How can I fix this?
    If you lifted the solder pads, there isn't much you can do.

    For this exercise, you are removing all the old solder.

    I like to add a little bit of solder first to the old solder/joint and then I use my desolder pump to suck everything up. Then I clean up with a little bit of alcohol and add fresh solder.

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Ok, so I was resoldering all the things you marked.
    When I removed 2 of the transformers, one of their pins were without that silver layer on the board, so the tins doesnt sticks well.

    I attached some pics, 1 and 2 are the same and the 3 is the other pin.

    How can I fix this?
    Attached Files

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Oh, thats not the blown fuse, its one on the top right on the pic.Next to the heatsink, only half of it is visible.
    Its the picofuse, but I replaced it the 1st time with a cristal one.

    Also the normal voltage in Europe is 220V, just saying, dunno if that affects.

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    Ok,went to buy the components but they didnt have the fuse at 125V.
    Would one of 220V do the job?
    See your pic at

    https://www.badcaps.net/forum/attach...6&d=1283482087

    See where it says re CAUTION:

    Others may have different opinions on the fuse, but the warning CAUTION is there for a reason. I know it is not the picofuse, but the same caution applies.
    Last edited by retiredcaps; 09-03-2010, 12:49 PM.

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Ok,went to buy the components but they didnt have the fuse at 125V.
    Would one of 220V do the job?

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    One thing im still not sure:

    Code:
    Desolder all 4 transistors and the polyester caps (between the transistors
    Is the polyester cap the 'K' cap from my first pic? Theyre 2 so it makes sense, but just to be sure.
    Yes, the K cap is what Krankshaft is referring to.

    About the dual diodes, yes they are.Theyre named "DXXX" and they have this printed on one side:

    YG902C2
    -->|--|<-- CI
    40 121

    I managed to unstick them from the heatsink.
    But how do I test them? I tried this but I dont know if its correct:

    - Black (COM) on 2nd pin RED on 3rd: 400
    - RED on 1st pin BLACK on 2nd: 400

    Those values are with the diode setting ( -->|) of the polimeter. Other combinations didnt show results.
    Yes, that is correct. Excellent job. 400mV (millivolts) indicates that the dual diode is good. A good diode should read between 0.4V and 0.7V.

    The things I need to resolder, I just need to unsolder them and sold again with new tin or is there any other action involved? I ask because the soldering on those things seems ok , at least on looks.
    One more thing, should I resolder those things marked as '?' on the 6th pic?
    Krankshaft writes to desolder (remove all the old solder) and resolder with new solder.

    Another analogy (I spelled it right this time) might be painting a door.

    You have a door that needs to be painted. For the most part the paint looks good, but it could use some touch up.

    The lazy way is to just put another coat over it without cleaning it or stripping it down to the wood. This is akin to reflow new solder on top of the old solder.

    The "proper" way to paint this door is to remove all the old paint, sand it down so that is smooth, apply protective coat, and then paint it. This is akin to removing the old solder and adding new fresh solder.

    Yes, resolder those ? marked items.

    PS. You have made huge progress in the last 24 hours. Keep up the good work.

    Leave a comment:


  • PlainBill
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by retiredcaps
    Yes, because you chose to ignore 3 people telling you 4 times to resolder the transformers. This problem with the Benqs has been known for about 2 years now. When people say you *must* resolder the transformer it is because they have experienced what you have.

    We can lead a horse to water ...

    A poor analog might be the following (I can see PlainBill shuddering right now). Imagine a car engine as the transformer. When the bolts holding down the engine are loose, it shakes all the components of car.

    You take the car to the mechanic (Eric the car guy). Eric says I can fix the loose radio, loose hoses, loose steering wheel, etc from all the damaged caused by the engine for $500.

    Eric also HIGHLY recommends that he rebolts and remounts the engine. It will cost $1000. You balk. 2 days later, the engine causes the same damage. This time Eric charges you $1000 because the engine caused more damage than the first time.

    Eric again recommends remounting and rebolting the engine, but this time it is $1500 because of more damage. You balk again.

    And so on ...
    Actually, that is an excellent analogy. You teach well, Grasshopper!!

    PlainBill

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Thanks again retiredcaps.

    If I didnt resolder the transformers, its because I wasnt sure which ones were them, until jetadm123 pointed them out.

    That being said, I also didnt research more, because after checking that the fuse and the transistors were blown, I thought that those were all the problems the PCB had.

    One thing im still not sure:

    Code:
    Desolder all 4 transistors and the polyester caps (between the transistors
    Is the polyester cap the 'K' cap from my first pic? Theyre 2 so it makes sense, but just to be sure.

    About the dual diodes, yes they are.Theyre named "DXXX" and they have this printed on one side:

    YG902C2
    -->|--|<-- CI
    40 121

    I managed to unstick them from the heatsink.
    But how do I test them? I tried this but I dont know if its correct:

    - Black (COM) on 2nd pin RED on 3rd: 400
    - RED on 1st pin BLACK on 2nd: 400

    Those values are with the diode setting ( -->|) of the polimeter. Other combinations didnt show results.

    The things I need to resolder, I just need to unsolder them and sold again with new tin or is there any other action involved? I ask because the soldering on those things seems ok , at least on looks.
    One more thing, should I resolder those things marked as '?' on the 6th pic?
    Last edited by capullaco; 09-03-2010, 05:23 AM.

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    One other suggestion.

    Once the new parts come in, check them all out of circuit to ensure they are good.

    When you get all the repairs done, put away the monitor for 2 days. Come back 48 hours later with post #21 printed and go through each sentence top to bottom and bottom to top (i.e doublecheck all your work).

    That will give your brain some time to process the repair.

    Additionally, BEFORE you power up. Doublecheck all the components again to make sure they are soldered in properly, oriented correctly (not backwards) and retest them with your mulitmeter "in circuit".

    Then and only then, apply power.

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    1. Those are the transistors that were originally blown.Theyre blow again (the left arrow actually indicates the trans,not the cap :p)
    Yes, because you chose to ignore 3 people telling you 4 times to resolder the transformers. This problem with the Benqs has been known for about 2 years now. When people say you *must* resolder the transformer it is because they have experienced what you have.

    We can lead a horse to water ...

    Here is the technical explanation why the transistors short out.

    https://www.badcaps.net/forum/showpo...&postcount=269

    A poor analog might be the following (I can see PlainBill shuddering right now). Imagine a car engine as the transformer. When the bolts holding down the engine are loose, it shakes all the components of car.

    You take the car to the mechanic (Eric the car guy). Eric says I can fix the loose radio, loose hoses, loose steering wheel, etc from all the damaged caused by the engine for $500.

    Eric also HIGHLY recommends that he rebolts and remounts the engine. It will cost $1000. You balk. 2 days later, the engine causes the same damage. This time Eric charges you $1000 because the engine caused more damage than the first time.

    Eric again recommends remounting and rebolting the engine, but this time it is $1500 because of more damage. You balk again.

    And so on ...

    2.
    Im not sure if they should be bridged... One is a pin of the 'K' cap of the 1st pic and the other one is a SMD named "JR10"
    If you follow the circuit green pcb trace you should be able to tell if they are on the same circuit path or not. If they are, then it is not a problem if they are bridged.

    I started here on these forums back in April 2010, but I can't remember a single case where a bridged connection has been documented as a problem.

    I asked a similar question. See

    https://www.badcaps.net/forum/showth...+solder+joints

    4.I tried to compare those bridged with the image posted here, but im not sure, so I marked them
    That is a good idea, but be aware that there are possibly many revisions of this board. Manufacturers can change the boards as they see fit.

    5.Two new blown transistors.I dont know if they were blow before, but theyre now.
    The picture's angle makes it hard to see, but those are probably dual diodes? They should have 2 diode symbols pointed towards the center.

    What measurements did you get for these dual diodes?

    6.Those are the things I have to resolder right? Are they marked correctly? What are those two things marked as '?' ? Should I resolder them also?
    Yes, resolder those. L indicate an inductor. T is a transformer.

    7.Finally, this is the bit I said it was burnt.but the transistor under it its fine.
    Some browning is normal. As long as the transistor underneath tests okay, it is fine.

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Ok, my mobile is working again.

    Took photos of 'problematic' bits:

    Code:
    Photo number. Description
    1. Those are the transistors that were originally blown.Theyre blow again (the left arrow actually indicates the trans,not the cap :p)

    2.The bottomside of those transistors.Those 2 yellow points,are bridged (they have continuity and the polimeter beeps with the diode/continuity beep setting).
    Im not sure if they should be bridged... One is a pin of the 'K' cap of the 1st pic and the other one is a SMD named "JR10"

    3.Those are another bridged point.The cap pin is bridged with a drop of tin that it was already on the board.I think its ok

    4.I tried to compare those bridged with the image posted here, but im not sure, so I marked them

    5.Two new blown transistors.I dont know if they were blow before, but theyre now.They have a heatsink and theyre glued to it.
    Also, theyre special and are larger with a hole for a screw. Its one piece, I mean its not a transistor glued to another one. Wonder if I will be able to buy that type of transistor...Also, I dont know they ID, but I guess the guy in the shop will know.

    6.Those are the things I have to resolder right? Are they marked correctly? What are those two things marked as '?' ? Should I resolder them also?

    7.Finally, this is the bit I said it was burnt.but the transistor under it its fine.
    Attached Files
    Last edited by capullaco; 09-02-2010, 08:51 PM.

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    Guess Ill have to change the fuse and the transistors again
    Read post #21. Look at the very last sentence.

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Ok, so I was going to resolder the transistors today,but tried the display first.

    Its broken again

    Guess Ill have to change the fuse and the transistors again

    Leave a comment:

Related Topics

Collapse

  • Caspar
    BENQ GW2780-T power board blown
    by Caspar
    Hi all, I am looking for some help in ID'ing some parts in an attempt to fix a power supply from a GW2780-T monitor. The power supply PN is 715G7300-P02-006-0V3R. I have been looking around for the PN and it appear the board was used by other OEMs as well (ASUS, Viewsonic). If anyone has a schematic, it would be helpful.

    Quick look on the underside of the board, I can see:
    -D905 is blown - ? value
    -R920 is open - 1Ω ?W
    -R927 is open - 20Ω ?W

    On top side, I see:
    -R931 open - 0.68Ω ?W

    Metered short:
    -P9NK65ZFP...
    06-01-2022, 05:16 PM
  • jean luc ferre
    laptop hp g72 b52sf screen problems
    by jean luc ferre
    Hello,
    on this laptop hp g72 b52sf i have screen problems as you can see with the photo joined in attachments.
    the used graphic card is "intel hd graphics" and the id of the integrated screen is : "monitor/SEC3354".
    i verified the driver of the péripherals and they are ok. i verified the definition and settings of the graphic card and of the screen : definition 1600x900 and refreshment frequency :60hz. (they are the sames for the graphic card and the screen).
    i don't understand the reasons of the white stripe at the bottom of the screen below the task...
    06-07-2025, 03:27 PM
  • drscoot
    HP X360 convertible battery blown fuse error, not charging
    by drscoot
    HP Modelnumber: 14-dh0061nb​
    This laptop had a shorted cap on a Vcore section. After replacement is works again. But there is still a battery issue.
    The battery is HT03XL and with the built-in component test from HP, in the Power section, I get an error: Logic State: Calibration required (20), Charge state: Blown Fuse (42)
    I have another same battery, also with error: Logic State: Very Weak (70), Charge state: Blown Fuse (42)
    And a third battery TF03XL (looks identical) with error: Logic State: OK (0), Charge state: Blown Fuse (42)
    All these 3 batteries are charging...
    12-15-2023, 05:54 AM
  • Hondaman
    USB problems?
    by Hondaman
    Recently I discovered my SSD died (OCZ/Toshiba 240 GB). It was in a USB enclosure, attached to the Linksys WRT-AC1200 router. Since then I removed the USB enclosure and attached it to my Win7 PC (AMD 8150 CPU, 970 chipset, 64 GB RAM). I also gathered one or two other USB enclosures to figure out what is going on.

    (I suspect that I lost quite a few MP3 and FLAC files I recently ripped from my audio CDs, I think I lost very little un-replaceable stuff.)

    I think it is IMPOSSIBLE for Win7 to have any problems with a USB enclosure as long as Win7 knows how to speak to the...
    08-12-2024, 03:26 PM
  • swerg
    Part selection for possible blown inductor on ASUS GX531-GW-AB76 laptop mobo
    by swerg
    Hey everyone,

    I'm a novice trying to repair my laptop. The LCD screen has an image, but no LED backlight for the image. It also produces an image when connected to an external monitor.
    I have found what I believe to be a blown inductor labeled "L4502" and "120 Ohm" in the schematics (zoomed in image, blue arrow to blown component). I have included an image of the general area of the mobo and an excerpt from the schematics as well.
    I am having trouble selecting a replacement component, which I believe to be a 120 Ohm ferrite bead, from the components...
    06-06-2024, 03:39 PM
  • Loading...
  • No more items.
Working...