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PPDB Rev A - 5V Regulator issue..I think — Parallax Forums

PPDB Rev A - 5V Regulator issue..I think

CassLanCassLan Posts: 586
edited 2010-04-08 02:03 in Propeller 1
Using the PPDB Rev A, haven't used it in a bit. I was using it fine with a 12V wall wart.

Anyhow, "No Chip Found" message from PropTool, and I looked at the Regulators, all around the 5V Reg is yellow/brownish, I touched the 5V reg and OUCH!.

And the DIP Prop is also very hot....

I switched to an 8V wall wart, let things cool down and still no prop found, the power LED on the PPDB stays on for a couple secs but then goes out, the Reg and Prop still get very hot.

Suggestions?

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Comments

  • YendorYendor Posts: 288
    edited 2010-04-07 14:46
    Isn't Rev A the latest?
  • CassLanCassLan Posts: 586
    edited 2010-04-07 14:48
    It could be, I was just proving as much info in case there was a newer one.

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  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2010-04-07 15:47
    Apart from the obvious dead Prop, my rant is usually the 5V on the VGA socket getting shorted to ground, but that should leave the Prop cold as it gets no 3.5V.

    If it is a long dissused board, has it·suffered a solder splat ?

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  • TonyWaiteTonyWaite Posts: 219
    edited 2010-04-07 15:48
    ... short between output of regulator and ground?

    T o n y
  • CassLanCassLan Posts: 586
    edited 2010-04-07 17:42
    Well, I checked with a meter..no shorts.

    But I placed another propdip in after measuring a crisp 5V of that Reg and 3.3 of the other, and it works fine.

    Maybe the prior propdip was put in backwards?

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2010-04-07 18:36
    Oddly enough, a reverse insertion probably would not hurt anything. Vdd and Vss still go to their proper locations. A reset would short XO momentarily but, without a program running, all the pins would be tri-stated and not causing bus conflicts.

    -Phil
  • David CarrierDavid Carrier Posts: 294
    edited 2010-04-07 19:48
    CassLan,

    There is a tantalum input capacitor on the PPDB, which is sensitive to overvoltage. Sometimes linear power supplies will output much more than their intended voltage when the current draw is low. The PPDB, in and of itself, doesn't draw much power, so your supply might have overvoltaged the input capacitor. Since it is a tantalum capacitor, it will very thoroughly destroy itself when the voltage is to high. (I have had them catch on fire before.) They usually end up shorting after they are destroyed, so chances are that your Propeller is unaffected, but your regulator's input is now shunted to ground. You may be able to continue using your PPDB by supplying regulated 5 VDC into the "5V" pins.

    — David Carrier
  • CassLanCassLan Posts: 586
    edited 2010-04-07 19:55
    Well I put in a different Prop Chip and it all seems to work well, including the 5V supply.

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  • DonEduardoDonEduardo Posts: 54
    edited 2010-04-08 02:03
    I blew up my PPDB within the first two minutes of receiving it. I plugged in a "12v" wall wart and SPLAT! Dead. I checked the wall wart and it was putting out about 17 volts with no load. That capacitor is only rated for 16v and shorted out. I removed it and everything was fine after that. I later replaced it with a 50 volt version that I had laying around (not surface mount like the original one).

    I guess that is not your issue though but responding to and supporting David's warning. Be careful of what voltage you actually put into the board.

    Or replace the cap.
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