Re: Messed up my Black Widow

Don't forget, the two 15V regulators do not run from the +5V supply. They run from the +/-22VDC supplies so they are not relevant in this case.

The trick is to determine where all the current is going. If you are having a tough time tracing it using thermal methods, and assuming that you don't have an old HP current probe, there are still a few other tricks.

If you have one of those toy magnetic sheets, the ones that change color and show a pattern when you hold a magnet under them, you should be able to hold it against the board and visualize the strongest field generated by the traces and components that are carrying the high current.

If you have a very small magnetic compass, like the ones on keychains, it should be attracted most obviously to the traces carrying the high current. The little "water ball" type would likely work the best.

William Boucher
http://www.biltronix.com
  ----- Original Message -----
  From: simon Hanlon
  To: vectorlist@vectorlist.org
  Sent: Monday, July 02, 2012 5:29 AM
  Subject: Re: VECTOR: Messed up my Black Widow

  I agree with Andre, I've used my ESR/ low ohms meter to find shorts in the past. They usually turn out to be ceramic caps.

   I'd be surprised if it was anything other than a bent pin or other basic problem on this case.

  I'm surprised you have warm voltage regulators if the board has a dead short, id expect them to be cold or very hot.

  Sent from my iPad

  On 2 Jul 2012, at 07:34, Andre Huijts <a.huijts@upcmail.nl> wrote:

    A good ESR meter can be used with this method too as it sends 100 kHz through the "test path" it is much more sensitive than a regular DVM.

    Verstuurd vanaf mijn iPad

    Op 2 jul. 2012 om 05:57 heeft Rodger Boots <rlboots2@gmail.com> het volgende geschreven:

      I don't think all the modal voltages in the world are going to help if power is shorter to ground.

      What works great (used to do it at work), but requires a damn good ohmmeter, is to find the most shorted point by measuring for it.

      I had a HP 34401 meter at my station. You lock it into the lowest ohm range and set it for 6-digit readings. Then enable min-max mode. Pick a starting point on the board. Meter will beep because you found a low reading. You then just walk your leads around looking for a lower reading. The last point that beeped is where the short is.

      But the frost-it-up method can be faster (I had a CO2 spayer available).

      I wonder if when he pushed the chips back in if a socket lead didn't just bend over on THE BACK SIDE of the board.

      On Jul 1, 2012 10:24 PM, "Christopher X. Candreva" <chris@westnet.com> wrote:

        On Sun, 1 Jul 2012, Joel Rosenzweig wrote:

> You could have an integrated circuit that has failed, causing the short.
> I've had failures with the TL082's (for example) that took the whole board
> down due to an internal short. These are very tricky to find. I don't know
> how to effectively troubleshoot that without removing parts one at a time
> (or at least lifting the Vcc leg).

        I wonder if it would be possible to do a nodal analysis ?

        For those who didn't take (or forgot) circuits 101, this involes simply
        measuring the voltages at various points in the circuit (called nodes, hence
        the name). I remember years ago fixing a WG color vector monitor, because
        Atari printed nodal voltages on the schematics (probably exactly for this
        purpose). With the help of people on this list I was able to determine where
        my boards voltages differed from the schematic, and what was the likely
        failure based on this.

        So the first quesion would be, do the Black Widow (Gravitar) schematics have
        nodal voltages on them anywhere that would be usefull ?

        ==========================================================
        Chris Candreva -- chris@westnet.com -- (914) 948-3162
        WestNet Internet Services of Westchester
        http://www.westnet.com/
        ---------------------------------------------------------------------------
        ** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
        ** Please direct other questions, comments, or problems to chris@westnet.com

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Mon Jul 2 10:54:18 2012