Question about IBM ThinkVision L170 17" LCD Monitor

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Suspect backlight inverter circuit--desktop appears completely for 1s and then loses backlight

Desktop appears completely for 1s and then loses backlight. Pushing the analog/DVI select button brings backlighting back on for 1 second and then drops. i suspect the inverter circuit as i found one 10v1000µf cap (C551) blown. I replaced this and its counter-part a 25v470µf cap (c661) with 25v1000µf and 25v470µf caps, respectively. Same symptoms. I am uncertain where to go from here as it would appear the backlight lamps are functioning and the inverter appears to work perfectly for about 1 second and then drops power to the lamps. I do not have a B.O.M. or schematic, so I am really troubleshooting blind. I suspect a protection feature is of some sort, but again, i have no schematic to reference. Where do i go from here?

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  • Noel Rusnell
    Noel Rusnell Oct 16, 2008

    To clarify, the first step in troubleshooting was to look for physical damage and re-seat cables, checking components one by one for visible signs of damage. I am unsure as to where to go from here. I do not typically perform shotgun parts replacement, but i do check each out of circuit. The lamps check out ok and all light up for one second. I am not understanding the cause of the inverter to be fully-functional for one second and then shut down. I am suspecting an over-voltage protection circuit or something of that nature--beyond the obviously failed and replaced 1000µf cap (C551) i am not sure where to go.for this symptom. Part of the problem is i do not have a schematic nor B.O.M. to reference.

  • Noel Rusnell
    Noel Rusnell Oct 17, 2008

    B+ is 14.44V, regulated 3.3v, 5v and 12v is present on the video processing board and 5v, 12v are both present on the power supply/inverter board. I am in dire need of a schematic to be certain, but i am leaning toward a faulty BIT3105 CCFL Controller as it has built-in dimming and over/under-voltage protection circuits as well as open lamp detection...a little more testing is necessary...a schematic with correct pinout values and B.O.M. would be really helpful here as i could better decipher the current path and TTL signal/switching processes. I am uploading images showing the power and inverter board along with the blown 10V1000µf cap and of the 1-second desktop--you can well imagine the fun i had timing the digital camera to capture the display ignition
    here is the link to the datasheet for the BIT3105 Controller:

    Pinouts are as follows:
    ϑ 7.43V on AVDD and PVDD
    6.96V on CMP
    1.25V on RTDLY
    ϑ 7.4Von NOUT2, NOUT1, POUT1, and POUT2
    1.52V on EA
    213 Kω on PWMOUT
    1.3V on CTPWM
    .6V on DIMDC
    3.9V on SST
    0~.4mVon CLAMP

  • Noel Rusnell
    Noel Rusnell Oct 17, 2008

    the one cap appearing to have the bulge is one i was super-imposing with a pair of forceps for comparison. its replacement is shown immediately below it in place and is taller by a full height than its counterparts. the four 25v47µf caps and the 2 pots are connected to the BIT3105 CCFL controller (top-center of the board) which i described in my previous post and whose 7.4Von NOUT2, NOUT1, POUT1, and POUT2 drive the N&P MOSFET switches on the back side of the board. the 4 lamps check out good; however it appears i need an inverter transformer SPI 8TT00006 as there is an open winding at pin 1 and pin 8 on T4 (labeled faintly in blue on opposing ends of the faulty transformer)

    So, here's the kicker...SPI 8TT00006 does not come up for any vendors i can find with a google search or even eBay. Any ideas? know of spares on unused inverter/power supply board for these models? closest i could find is a long shot by Delta Electronics with stock number CIT011. your take?

  • Noel Rusnell
    Noel Rusnell Oct 19, 2008

    in the end--even those electronics suppliers who list the part as "available" on their websites, don't...and their techs and sales staff do not know what they are when contacted directly and have had to get their engineers working on locating a match. I've been waiting for a call back from the suppliers as to whether they can even do that...the customer has opted not to wait and picked up the old LCD...what for, i don't know...maybe all the troubleshooting was really what they were after all along. I suppose i could have or might have been able to use the unit for parts...shame they wouldn't at least wait for a response from the suppliers. back-up plan was to check e-Bay for a parts unit, but they refused to wait...

  • Noel Rusnell
    Noel Rusnell Nov 03, 2008

    thank you,

    kenny258...great suggestions--sadly, i no longer have the LCD to try these workarounds; however i am most certainly keeping this page bookmarked for future reference.

  • Ngewakl Soaladaob May 11, 2010

    I had the same problem but I had loose connection on my inverter board. I assume you have reseated your board?


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"Latched Open Lamp Protection Pin 4", disconnect the transistor 7002 "D" Pin on BIT3105 Pin 4.

Posted on Oct 30, 2008

  • kenny258 Nov 03, 2008

    Solution of Transform 8TT00006.
    1, I have been use an old Compaq laptop single CCFL transform to do the job.
    2, Or pull out 2 transforms and put in a bigger one for 2 CCFL, you can keep the good one for spare.
    8TT00006 primary only use 2wire that easy covert to other transformers, just let the CT pin
    ps; May be you need disable "open lamp protection" Pin 4 (lamp current unbalance).


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I had just the same problem and suspected the BIT3105 IC, but this was working well. It was just in protection mode because of a broken hi-voltage transformer (one of the four). All the secondary outputs of this transformers have a resistance of 1 kOhm, but that one was open! By removing it from the circuitboard it was clear. On the bottom of the transformer was a black spot from a "spark-bridge". All the CCFL tubes were good. So it must be a production fault. The only thing you can do, is find a new or similar type of transformer and try to put it back. (maybe from an old TFT monitor)

I think this is also the problem by a lot of people here.

Best regards,


Posted on Feb 02, 2010

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Hi i need the type number of ic u302 can you tell me the type numer of this ic ??? i have the same power supply but the ic u302 is burned up and now i cant read the type numeber..

send a mail to



Posted on Sep 26, 2009


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Hi I'm not very proficient with these technologies but I think the blockade is produced specifically SOP-8 mos additional power, Branding: A or P First line: 4600 Second line: BB03N15 or AD3S3L, which are responsible for the blockage of energy. ..

Posted on Sep 18, 2009

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If you find one blow capacitor, you should change out all of them.
The large main one can usually be left go but for 6 bucks it is wiser to change that too while it is apart.
If that doesn't cure it then you have to move on to the transistors that run the backlight transformers.

A NOTE: you could have one failing bulb. Not sure if yours has 2 or 4, but it only takes one bad or weak bulb to give you the same effects.


Posted on Oct 15, 2008

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  • Fran Bednar
    Fran Bednar Oct 16, 2008

    Finding a schematic is worse than finding some of the parts
    forthese or any boards. They are secretly stashed with the creators.
    bulb going on for a second is not long enough to tell if it is
    good(especially if it is still in the screen and you cant watch
    it'sreaction) easiest way to test them is with the use of another
    Being 17s are older units, this is a common failure in these.
    What are you showing for dc voltage at the connection to the video board ? Most older units run 5 and 12. Some just use 5vdc.
    looking caps are not always good caps. Standard cap meters don'talways
    give the most accurate info. An ESR meter is the best to use.But it's
    cheaper to change all the caps then to buy a meter and sincecaps are
    the most prone to fail with age, now is the time to changethem all out
    if your showing some dc which you should have since yousay you have a
    picture for a bit.
    If you have a picture, post it or email it to

  • Fran Bednar
    Fran Bednar Oct 17, 2008

    DC values appear typical.

    The screen picture looks darker on top than on bottom..

    DID you individually check the bulbs ?

    Plugging them in ONE AT A TIME to get the flash on the screen may help
    tell especially if you disconnect the video to lcd ribbon (that will
    give you just a white screen and make their brightness a bit more

    Best way to test each is using another monitor as a power source- It only takes one to stop these boards in their tracks !!

    It almost looks like the one cap is bulged on the picture (could be the picture?)

    I don't see the transistors the the ccfl transformers, (Probably on the
    back of the board between the ccfl transformers and under the 4 caps )
    If it's not a bulb , I would think these are more likely the suspects
    than the actual ccfl control board. Check to see if any are grounding
    out against the positive DC side.

    Again. Schematic WOULD BE GREAT !! But !!?? I have to trace just about every board I work on since I can't find them either !!

  • Fran Bednar
    Fran Bednar Oct 17, 2008

    I thought that capacitor looked out of place !!

    There is always a kicker !!
    Now More FUN finding the part !! ??
    one inverter I've done uses one transformer to one ccfl and thatis a
    Benq, but those are square shaped. All my other boards use oneTrans for
    2 lights.
    That one is almost light a laptop transformer.

    You can maybe get lucky and get a cross reference from ??
    LOT OF WORK for a 17" screen !!!
    It appears you are like me ! PERSISTENT !!

    This may help finding a substitute

  • Fran Bednar
    Fran Bednar Oct 19, 2008


    If you want an ebay parts unit, wait a while (YOU'LL SEE THIS ONE SHOW UP !!!!! )

    Can't please all the people all the time !! All you can do is try !!

    Thanks and have fun



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