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Problem with auto LCD display install

Discussion in 'General Electronics Discussion' started by david3264, Apr 6, 2013.

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  1. david3264

    david3264

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    Apr 6, 2013
    I've been replacing an lcd display that goes into an Audi car. The display sits in the center of the dash and gives info about condition of car and info such as speed, mpg, eta stuff like that. I've been repairing auto electronics for 8 years now so I'm good at soldering but am kind of new to these lcd displays.

    The display doesn't act right and I've installed 4 of them in this same car thinking I may have had some faulty displays as the first 2 I tried were Chinese made. I then bought some more expensive European made lcd displays and tried 2 of them only to get the same results.

    Here's what the display is doing if you'll go to this link


    This link describes the repair I'm trying to perform and as you can see, its pretty straight forward.

    http://www.audiworld.com/tech/elec183.shtml

    I've done about 4 of these repairs, had success on 2 of them and 2 of them did exactly what is being shown in the video. The 2 I had success on initially didn't work but on the second attempt, the screen worked fine so the odds of this being a bad instrument cluster is very low and I've had no luck trying to find Audi owners that had bad clusters so this is something I'm doing wrong but can't figure out what it is.
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    hi david

    welcome to the forums :)

    you have commented about buying displays from 2 different regions. But you didnt comment if either of these choices were genuine Audi replacement parts ??
    If they are not, that may well be your problem.
    ie.... other lookalike parts will work ... sometimes!!
    just a thought :)

    Dave
     
    Last edited: Apr 7, 2013
  3. david3264

    david3264

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    Apr 6, 2013
    Dave,
    Thanks for replying. No, these are not official Audi replacement parts and the reason that is, is because Audi doesn't sell them nor does VDO which is the company that originally made the cluster for Audi. If you were to take your Audi car to the dealer and say you wanted the instrument cluster display fixed, all they would do is try and sell you a complete, brand new cluster for $1000+.

    This is why there are a few guys like myself that will take apart the cluster and just replace that particular part so you don't have to get a whole new cluster. There are 2 ways to acquire these screens, one from a company in Europe which has the highest quality screens and the other place is China. I have tried both in this case.

    The majority of my business is with BMW clusters but the LCD screens placed on those are "bonded" in and not soldered. These Audi screens are soldered in and I just don't know what the problem might be. It almost appears as though its a bad display driver on the screen but 4 in a row ? I just think it has something to do with my installation and I was hoping someone with experience with similar screens might say "Oh, yeah, I know what your problem is"

    I know that might be a stretch but I'm desperate now. Thanks for taking the time to reply
     
  4. sheldonstv

    sheldonstv

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    Jul 17, 2007
    looks like it could be due to poor soldering on that ribbon connector or faulty connection ribbon to lcd itself
     
  5. david3264

    david3264

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    Apr 6, 2013
    Well, that's kind of what I was thinking but I'm not sure why my soldering would be so poor. As mentioned I've been working on electronics for 8 years now and solder components onto circuit boards on almost a daily basis. This problem has happened too many times for me to think its the LCD screen or its attaching ribbon as I can't believe these screens would be this poorly made, I don't think they would even be offered for sale anymore and they've been on the market for a few years now.

    Let me go over my soldering technique and you experts can critique me. I remove the original screen using same way shown in that link, I use Chip Quick to get the old ribbon off. I then clean the solder pads off with some ketone and "tin" them with fresh solder. "Electronics" (60/40) solder is used. I use a Aoyue brand soldering machine with a very small tip and a temp of 425 deg. I tend to use a little lower temp because if I knock one of the solder pads off the instrument clusters circuit board where this LCD screen makes contact, due to too much heat, I might be a out a lot of money as I'm not sure I can replace the pad. I don't have a solder pad repair kit of any kind

    I tin the contacts on the end of the LCD's ribbon cable but I've noticed if I tin the contacts after taking the screen out of the package, the solder will actually peel right back off the contact and expose a nice, shiny copper surface underneath. To prevent this, I take an Exacto knife and scrap each contact enough so that I expose that copper surface, add a little flux and then tin each contact. I tried scrapping or peeling the solder off and it seems to be on the contacts good.

    I then place the LCD screen over the circuit board and line the contacts up. There are actually 2 holes drilled through the circuit board and I made a small plastic clamp that holds the ribbon cable down and once I align all contacts, I tighten the little clamp and it keeps the contacts lined up for me while I solder them. The clamp doesn't interfere with any component on the circuit board.

    I'll take my solder tip and move it back and forth across the top of each contact so that it'll solder to the contact beneath it and that's pretty much it.

    Is my solder temp too low ?? Does the Chip Quick need to be completely cleaned off the solder pads even though I don't think there's any on there. Can Chip quick interfere with making a good solder joint if it mixes in with the solder ?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    425F is too low and 425C is way too high. -- So either way, I think that's wrong.

    For 60/40 solder. I'd be using 320C to 360C probably... (I can't actually remember. I just know where to turn the dial to (blush). I'll check it out when I go out to the workshop next.

    OK, I googled it. That's about the temperature range I use for leaded solder.
     
  7. david3264

    david3264

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    Apr 6, 2013


    So 393C comes out to be around 600F so if I went over these contacts with a 600F soldering tip you think that might make a diff ?? Reason I ask is because the cluster has been reassembled and was about to be shipped back to the guy that owns it but if that might make a diff, I'd take it back apart.
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    393C is hotter than I would normally use.

    The temperature you want is the one which allows you to quickly bring the joint up to the temperature needed to melt solder and to allow it to flow over the joint.

    This really has a lot more to do with the thermal properties of the joint than the actual temperature of the iron (as long as it's hotter than the melting point of solder).

    I have the iron hot enough (i.e. minimum temperature) to allow me to solder the joint with about 2 seconds of application of the iron. (no need to be too anal about it, but I'd start near the bottom end of my range and turn it up a bit if the temperature seemed inadequate)

    If these are small joints, I'd be going for the lower range to start with.

    To answer an earlier question... I've not used chipquick, but I would imagine that you want to leave the pins and pads with no more on them than is needed for them to look "tinned".

    I'm sure it does mix with normal solder (that's part of its job) and I have no idea of the properties of the joint it may produce.
     
  9. david3264

    david3264

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    Apr 6, 2013
    I'm sorry, I meant to say 320C, not 393C, is about 600F. The solder pads are about 1/4" long and 1/16th wide so they're a "strip" but I was using just enough temp to melt the solder which is why I was using a lower temp. I was using low to help protect the solder pads because in the past, I have knocked a solder pad off of a circuit board but in those cases I could easily use a "jump wire" instead but with this LCD screen, a jump wire wouldn't work so I was making sure I didn't damage any of the original pads.

    I might just take the thing back apart and go over the joints with about 320C as I don't think I've got much to lose here. I don't know if you went to the link that outlined the replacement procedures for the LCD screen but it should be a simple job but I don't know why I'm having so much trouble performing it.

    Thanks for the reply and if you come up with anything else, please let me know.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,496
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    Jan 21, 2010
    Yeah, start with 320 and adjust as needed.

    The problem is not so much temperature, but heat. A soldering iron that is not hot (temperature) enough needs to be held on much longer causing more heat (energy) to be transferred into the joint. This heats (temperature) up a lot more of the surrounding components etc, potentially causing damage.

    A hotter iron will heat up the joint, allow the solder to melt quickly, yet leave the surrounds cool so that the heat can escape into them and allow the joint (and everything) else to cool more quickly.

    Be careful that you don't leave the joints on a flexible PCB (indeed any joint) under tension as that will lead to failure in an environment with vibration (like a car)
     
  11. david3264

    david3264

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    Apr 6, 2013
    Ok, I'm going to try this again before sending it back. I'll try your temp recommendations and report back tomorrow. Thanks !
     
  12. david3264

    david3264

    14
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    Apr 6, 2013
    I went over all contacts with a temp of about 580F and the display acted much better. I then went over them again but this time I took a dental pick and pressed down on each contact as I heated the joint in order to get a better contact and I think it might have helped. The dental pick didn't pull away any of my heat.

    However, I never could get it perfect but it looked pretty good. So there's no doubt my problem was that I was just not getting enough heat on those joints. This is an installation that seems to require a perfect joint on each contact in order to be successful but now that I know what the problem is, I think the next one will go much better.

    Thanks Steve for pointing me in the right direction here and recommending upping my temps. Thanks to everyone else that responded to.
     
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