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What's the best way to desolder/rework near plastic connectors that may melt?

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    What's the best way to desolder/rework near plastic connectors that may melt?

    Hi guys
    I'm pretty handy with a heat gun and consider myself quite skilled with a soldering iron

    However a repair I am working on right now has me raising an eyebrow, or two.

    It's a controller board of a 1Tb hard disk. The original one has a short circuit on the 12V rail that I have not been able to find. The owner wants to access the data on the drive.

    I have a replacement working controller board (same make/model/revision) but I need to desolder the bios chip from the faulty board and use it to replace the bios ship on the good board.

    Unfortunately the Bios chip is right near the SATA connector and I think that may melt during the rework process

    The best idea I can come up with at the moment is:

    1. Unsolder the Bios chip from the faulty board using the hot air gun.

    2. Cut the legs of the Bios chip on the good replacement board near the body, then remove the legs from the PCB individually using my soldering iron.

    3. Clean the PCB pads on the good board then solder the Bios chip taken from the faulty board using my soldering iron only and 60/40 solder.

    Is that the way to do it without damaging the SATA connector or is there a better way?

    Cheers
    Rich
    Attached Files
    Last edited by dicky96; 04-21-2017, 12:49 PM.
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    #2
    Re: What's the best way to desolder/rework near plastic connectors that may melt?

    soldering iron off and on ..
    use chip quik alloy to make it easier if your iron wont do it without .
    http://www.chipquik.com/store/index.php?cPath=200
    Last edited by petehall347; 04-21-2017, 02:33 PM.

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      #3
      Re: What's the best way to desolder/rework near plastic connectors that may melt?

      When you say heat gun, do you mean a device used for stripping paint ?
      I'd be using my hot air station angled away from the connector, low air flow rate and get up close with the 8mm nozzle.

      Comment


        #4
        Re: What's the best way to desolder/rework near plastic connectors that may melt?

        I cover the area with Kapton tape to protect plastic and other components that I don't want heat on.

        https://en.wikipedia.org/wiki/Kapton
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          #5
          Re: What's the best way to desolder/rework near plastic connectors that may melt?

          Protect the sensitive parts with aluminum tape or kapton tape and apply controlled heat, BTW these connectors seem to handle heat quite well, just make a test with a scrap drive.

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            #6
            Re: What's the best way to desolder/rework near plastic connectors that may melt?

            you take the old solder out by melting new one and mix it. use wick to take it ou then stuck in the oven. 100% of repairing keyboard,mouse,lcd connectors
            Just cook it! It's already broken.

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              #7
              Re: What's the best way to desolder/rework near plastic connectors that may melt?

              Yeah I meant my hot air desoldering station when I said heat gun - I always call it a 'heat gun' probably as it is easier to say lol.

              I often use the technique of mixing 60/40 with the lead free solder onboard to make it easier to desolder with heat braid, and melt some flux paste to rub the braid in first.... or 'Pasta do Lutowania' it says on the tin.

              Thanks for the info on Kapton and Chip Quick Alloy they are both new to me, will look into those.

              Cheers
              Rich
              Thanks for the
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                #8
                Re: What's the best way to desolder/rework near plastic connectors that may melt?

                Originally posted by dicky96 View Post
                Hi guys
                The original one has a short circuit on the 12V rail that I have not been able to find.
                I know it's not on topic, but isn't it one of the diodes near the power connector? Those 0 ohm resistors could be in bad shape too. Also I see a Smooth L7251 (I think) motor driver, I've replaced a few L6283, so maybe those could fail too.

                Now on topic, either I use some Kapton tape, but it doesn't isolate that well from heat so don't put 450°C for a few minutes, the connector will still melt, or I desolder using the soldering iron.
                SOIC-8 parts or similar shouldn't be too hard to desolder with the iron, you can use solder wick or form big blobs of solder on each side that you heat one after the other while gently lifting up the chip. (be patient as you could rip some pads if you try to do this too quickly)
                OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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                  #9
                  Re: What's the best way to desolder/rework near plastic connectors that may melt?

                  Hi Piernov

                  just staying off topic
                  The avalanche diode connected across the power connector do sometimes go short, probably if there was a voltage spike or PSU problem, I believe they are there as protection devices anyway and I have resurrected a drive or two by removing them, so I can power the drive up and access the data..

                  That isn't the problem on this board, neither is it the filter cap across the 12V SATA pins.

                  I did connect board up (removed from the drive) to my bench PSU in CC mode and slowly brought the current up to see what was getting warm. At a couple of volts and about an amp or so there was an inductor warming up nicely so I guess that is a buck regulator circuit.


                  That was a while ago as I put it on one side a few weeks back waiting for the replacement board off ebay (chinese supplier)

                  I guess I could go back and investigate the short more closely now, seeing as I have a doner board. If you think that is the more worthwhile approach I will start another thread for that topic.

                  Rich
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                    #10
                    Re: What's the best way to desolder/rework near plastic connectors that may melt?

                    Actually I decided it would be educational to find the short, even if I then take the bios chip and fit it to the replacement board.

                    Just had another look to remind myself, as it is some weeks since I last looked at the board.

                    The pics on this thread are the replacement, not the faulty board.

                    The short is not on the 12V rail it is on the 5V rail. It measures 0.3ohm to ground, not absolute zero ohm short. Yes I checked my meter is reading zero properly :-)

                    Will power it from the bench supply set to 5V in CC mode again later and see what it was that was getting warm as I forgot by now. Will start another thread to keep this one on topic.

                    Rich
                    Last edited by dicky96; 04-22-2017, 06:03 AM.
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                      #11
                      Re: What's the best way to desolder/rework near plastic connectors that may melt?

                      In some situations I use some top cover shields from old phones.
                      One that are full,not with holes.
                      I have many sizes and shapes.Usefull when desolder micro USB socket when near are plastic components,flex connector cables,handsfree socket etc.

                      Not much heat,not much air flow,just how much is needed to melt solder.

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                        #12
                        Re: What's the best way to desolder/rework near plastic connectors that may melt?

                        Was gonna put this on another thread to keep it on topic but there does not seem to be a specific section here that would cover hard drive repairs.

                        Anyway I had another look at this on "piernov's" advice, The drive is a Western Digital WD10EURS. It had a short on the 5v rail. Using my bench power supply in constant current mode I put a controlled amount of current through the short circuit rail and gradually ramped up the current to see what was getting hot.

                        One burnt finger tip later I found a capacitor near to the Smooth Motor Driver chip. In fact I had put enough juice through it so it became visibly distreesed, it was not like this befoe as i had examined the board closely trying to find the short. Anyway this was the cause of the short circuit. I've removed the capacitor and the short has gone.

                        It took a surprising, to me, amount of heat from my soldering iron, using flux and 60/40 lead solder - plus some preheat from my hot air station - to get it off the board. But it came off. Actually it broke in half in the process and I had to unsolder the second end separately.

                        So there is no short on the board any more which is a good sign. The cap is directly on the 5V rail to 0V near the motor control chip so to me that says decoupling cap. I suspect if I power up the drive with this component removed it would probably work anyway. Measuring across the two pads where I removed the Cap I see about 2000uF so there is plenty of capacitance on that rail anyway. The good board reads about the same.

                        Some pics of the bad cap and the desoldering job attached. I'm not experienced in working on anything as tiny as this and I hope I did OK by you guys standards. First one shows the fault cap (just above where it says C19) and next two the results of desoldering.

                        This has been an interesting job for me and raises a few more questions in my learning process - will put them on separate threads to keep on topic

                        Cheers
                        Rich
                        Attached Files
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                        https://www.youtube.com/channel/UCFX...R8UZ2vg/videos

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                          #13
                          Re: What's the best way to desolder/rework near plastic connectors that may melt?

                          Just thought I should mention..... one hard drive resurrected and working fine minus the decoupling cap
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