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  • EEVblog #405 – Lecroy 9384C Oscilloscope Repair – Part 3

    Posted on December 30th, 2012 EEVblog 14 comments


    A followup to the previous attempted repair video, clearing up a few things and removing the ASIC chip.
    Part 1 HERE
    Part 2 HERE

    Forum Topic HERE

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    • Britt

      To quote Bones… “He’s dead, Jim…”

    • MG

      When I was a kid I used to make keyrings with dead chips, and found a good method for removing QFP and SOIC ICs without damaging the pads or the leads, and without using a soldering iron. Just push the blade of a small screwdriver on the knee of the pin (just above the soldering pad) toward the center of the IC. The solder joint will break and the pin will bend a bit toward the center of the IC, but they will both be reusable afterwards. With some practice you can do more than one pin at once. Try it with another ASIC, you’ll be surprised! :)

    • Vegard

      Isnt there a chance damaging the pads when doing that?

    • tchicago

      I thought you’ll use the Chipquick. But it is kind of expensive stuff to waste on this.

      • robert

        Nah! You only need a tiny amount of the alloy.

      • http://www.eevblog.com EEVblog

        I can’t use what I don’t have.

    • MarkL

      I think the only thing left to do is to check the removed ASIC for the short between one or more of the 3V3 pins and GND. Should be around 0.4 ohms aggregate based on the other readings in-circuit.

      The scope is obviously beyond repair at this point, but this would be a final verification that it’s the ASICs.

      (And I have to second the use of Chipquick. I’ve used it to replace 208 pin TQFPs with zero damage. It’s really magic stuff and worth having on-hand.)

    • daqq

      Couldn’t you use a DC magnetic field current tracer like the 574A to find the short?

    • xDR1TeK

      No one would have gone to that length to fix the damn thing. Though we learned many ways to go about fixing it and that was the purpose I would say. Give it a good prayer and send it off.

    • Ian

      I don’t think I would be able to sleep at night without removing each one of those ASICs and verifying indeed that they are all shorted. At this point, I just want to know what the heck is wrong with the board even if it is no longer reparable. I am already having troubles sleeping at night after following this series. Thanks Dave :D

    • f4eru

      One clever way to desolder the chip without destroying anything is to put a .3 or .5mm lacquer wire under one row of pins, solder one end to a pad, and pull the other end away from the chip horizonthally, while heating the last pin, then the following one etc.
      The wire passes under each pin, lifts it and separates it from it’s pad. Clean removal !!!

    • ac

      I wanted to report about an “oven trick” that sounded too good to be true but appears to work in specific cases for “beyond repair” type of cases.

      There are certain computer components that get really hot, like high end graphics cards. A particular symptom that seems impossible to repair is various graphical distortions. In my case, red and blue lines and text characters being all wrong in the text mode. (replacing the single swollen cap didn’t help)

      After some searching I came across claims that removing all the heatsinks and such and putting the card in a convential cooking oven for 5-10 minutes at 190 c will cure the problem. Sounded rather unbelievable, and the smell after doing this was really bad too but it did fix the card. Most often this has been reported to work on a 88xx series Nvidia cards which have been very popular. There’s a great deal of youtube videos of people cooking their broken hardware. I gauged about 70% chance of success judging from comments.

      I put a small cut of solder next to the card which I had partially foil wrapped the capacitors and plastic parts to try prevent them heating up as much (not sure if it did help or not, one white connector went brownish as I read about 210 c on the card even though I had set the oven to 190 c).

      The solder visibly melted but I didn’t see anything happening on the card itself and inspection afterwards it doesn’t really seem like the solder reflowed anywhere even though I read 210 c, though I can’t really tell from under that BGA or whatever they use for the GPU chip itself. In anycase, I put the broken card back to computer and problems are gone. I’ve yet to put it through any intense games though.

      Now the most interesting bit that I didn’t really try was that someone claimed being able to repair dozens of Xboxes just by warming up the motherboard four couple hours in 70-100 c range. The theory was that this would “de-warp” the board or something, from the pressure the heatsink attachment puts into the board and when its warming & cooling a lot in use will cause it to show error when powering up.

    • tony stewart

      David,
      Nice try on laCroy.

      I wish you had traced the voltage drop on the 3.3V. If it was linear one would have expected 3.3V/.16 ohm = 24Amp …
      Assuming your meter was nulled.

      Always apply Kirchoff Laws for short tracking to source. It was possible your leads were getting warm too but I did not see you test those. Your internal supply was reading near 0V, How do you know your external supply was reading 3.3 on the board?

    • Dave C.

      This repair blog is better than the the ones that end in “success”. This time you showed us ALL the troubleshooting tools in your kit. If you had found the cause earlier you would have stopped and replaced the culprit and we wouldn’t have the benefit of your ‘shooting talents.

      Thanks!