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The dreaded PLL failure & soldering QFN's — Parallax Forums

The dreaded PLL failure & soldering QFN's

JonathanJonathan Posts: 1,023
edited 2010-06-06 19:51 in Propeller 1
Hi All,

Looks like I have suffered a PLL failure. At least, the prop accepts a program but won't run it. I have tried with a simple PST program that I use as a template, so it is a known working snip. Any other ideas?

The prop in question is on a protoboard. I have a fair amount of work into the board. So, I'm wondering how hard it would be to desolder the old one and solder on a new one. Mostly what is soldered on the board is headers, so it all should be fairly heat resistant.

Thanks!

Jonathan

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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-06-05 15:04
    Everyone, or no one else, will ask about whether you've landed all of the +V and GND pins and about all of the decoupling caps, too.
  • JonathanJonathan Posts: 1,023
    edited 2010-06-05 15:16
    PJ,

    Yup, it's all there. It is on a protoboard, so the caps etc. were done by Parallax. This is a project that has been running for a long time. I added a transistor to be able to control a load and poof. I have DC'd the new circuit and no joy.

    Jonathan

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    www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
  • LeonLeon Posts: 7,620
    edited 2010-06-05 15:16
    You presumably mean the QFP chip on the Proto board, rather than a QFN part. Use Chip Quik to remove it. Replacing it with a new chip is easy if you drag-solder the leads after tacking down leads on opposite corners.

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    Leon Heller
    Amateur radio callsign: G1HSM
  • wjsteelewjsteele Posts: 697
    edited 2010-06-05 15:19
    Removing the old prop is no problem. The easiest way is to cut all the legs first with very small snips, then simply 'heat and wipe' the legs towards the center. They'll come right off nice and clean.

    Then you'll want to reheat the pads and push the solder back to the outer edge so that you can push it back on the new props legs.

    Bill
  • jazzedjazzed Posts: 11,803
    edited 2010-06-05 15:22
    Guess it depends on how close the headers are .... I use an 800F degree heat gun and it works without affecting other components too much. Just make sure to put flux on the chip first. I've tried the old exacta-knife hack to take a chip off the older Propeller Proto-Boards and ended up losing traces :< ....

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    Propeller Pages: Propeller JVM
  • RaymanRayman Posts: 14,887
    edited 2010-06-05 20:19
    It's not easy to remove the Prop without damaging pads...

    One way that sometimes works for me is to put solder all the way around so that there's a big bead between all the pins.
    Then, if you're lucky you can use a hot iron to keep all 4 sides liquid for a nanosecond...
    Then, you move it off the pads somehow before it solidifies...

    But, Prop removal was the reason I bought a hot air gun. It's really easy to remove chips with it!

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    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm

    My Prop Products:· http://www.rayslogic.com/Propeller/Products/Products.htm
  • T ChapT Chap Posts: 4,223
    edited 2010-06-05 20:35
    If you don't have a rework air tool, you can use a heat shrink gun, if needed put some tin foil around the nozzle to reduce the air size to a smaller area. I have use hot air gun to lift tons of parts, it just takes a little while to heat it up. Put the other chip back the same way to use a pencil, use flux over all the pins to reduce bridges, since you can sort of smear the excess solder around until the solder stacks up evenly over the pins and the bridges disappear.
  • LeonLeon Posts: 7,620
    edited 2010-06-05 20:41
    Rayman said...
    It's not easy to remove the Prop without damaging pads...

    One way that sometimes works for me is to put solder all the way around so that there's a big bead between all the pins.
    Then, if you're lucky you can use a hot iron to keep all 4 sides liquid for a nanosecond...
    Then, you move it off the pads somehow before it solidifies...


    It's much easier to use Chip Quik:

    www.chipquikinc.com/

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    Leon Heller
    Amateur radio callsign: G1HSM
  • JonathanJonathan Posts: 1,023
    edited 2010-06-05 21:39
    Thanks for the suggestons folks. I do have a heat gun, paint/heat shrink type. I'll make a nozzle for it. I may order a chipquick setup too. I hope I can get it to work, I'd hate to have to redo the whole board.

    Thanks!

    Jonathan

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    www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-06-05 22:15
    Ken Gracey's been giving away the store lately.· I·bet if you do a heavy sigh coupled with a solid·"Oh, me" he'll get you another straight away.
  • Zap-oZap-o Posts: 452
    edited 2010-06-05 22:31
    Look the BEST way to remove any surface mount device is to use solder wick and a heat gun.

    If no heat gun, then solder wick and a soldering iron but this can damage pads on the circuit board so look out.

    Cutting the pins off is also a good second choice then use solder wick to remove the old solder.

    Soldering a new IC is just as easy, one way is to solder each pin carefully. The other way is to "GOB" all the pins and remove excess with solder wick.

    tongue.gif

    I solder 0603 resistors and surface mount IC's just about every other day so if you need any questions answered just ask.
  • whickerwhicker Posts: 749
    edited 2010-06-05 22:48
    Jonathan said...

    This is a project that has been running for a long time. I added a transistor to be able to control a load and poof.
    Jonathan

    Let me guess, an inductive load or dc motor?
  • RaymanRayman Posts: 14,887
    edited 2010-06-06 01:14
    Leon said...

    It's much easier to use Chip Quik:

    www.chipquikinc.com/

    I think so too.· I bought some a while ago, but never used it.

    The quad packages are the only ones I have any trouble with, and with the hot air gun, they're no problem at all...

    At home, I've used two soldering guns, with the way I've described, to remove a Prop.

    If you can afford the $300...$500 for a hot air gun, it's well worth it.·· As long as it's not your own money anyway [noparse]:)[/noparse]

    I do know the pain of having a lot of stuff on a Protoboard and then having the Prop die...· This is actually my main motivation for PropBox Prop.
    If you look at "messybox2.jpg" on this thread http://forums.parallax.com/showthread.php?p=904203
    I had to change out that chip.· I uses snippers to cut the pins that time, but some of the pads were damaged in the process.· That's when I bought the hot air gun...

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    My Prop Products:· http://www.rayslogic.com/Propeller/Products/Products.htm
  • jazzedjazzed Posts: 11,803
    edited 2010-06-06 02:06
    Rayman said...
    ... If you can afford the $300...$500 ...
    My hot air gun was $29.95 ... Milwaukee 1400 works great [noparse]:)[/noparse]

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  • RaymanRayman Posts: 14,887
    edited 2010-06-06 16:50
    jazzed: Thanks for posting that! I had no idea there was a low cost hot air gun that would work.

    Is that one adjustable in temp or airflow at all?

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    My Prop Products:· http://www.rayslogic.com/Propeller/Products/Products.htm
  • jazzedjazzed Posts: 11,803
    edited 2010-06-06 17:28
    No Rayman, it's fixed at 800F.
    I've used it to remove lots of QFP, SOT, and TSOP parts without damaging PCBs.

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  • JonathanJonathan Posts: 1,023
    edited 2010-06-06 19:51
    whicker said...
    Jonathan said...

    This is a project that has been running for a long time. I added a transistor to be able to control a load and poof.
    Jonathan

    Let me guess, an inductive load or dc motor?
    Oddly, no, it wasn't inductive. Just a GPS.

    Thanks for all the help. I'm going to try removal this afternoon, and if that goes well I'll order one up on Monday.

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    www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
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