Re: Vcc buss rails being pulled down.

I think that the odds are that it is a shorted electrolytic or tantalum
capacitor so maybe check those first.

Usually the shorted component gets warm, at least significantly warmer than
the others (not counting the shorted regulator). You can use one of those
handheld gun type infrared temperature measurement tools to see which chip
is taking all of the current and heating up. It only takes an increase of
couple of degrees to find it.

Another method, I don't know if they are still available but I have a probe
called a "short squeak". It looks just like a typical logic probe but it is
designed specifically for finding shorts like yours. It generates a audible
tone the goes up in frequency as you get closer to the short. It has two
probes so all you do is "measure" across any two points and listen. The
higher the pitch, the closer you are to the short. It is amazing how fast
you can track down which device is faulted.

William Boucher
http://www.biltronix.com

----- Original Message -----
From: <litterbox99@mchsi.com>
To: <vectorlist@vectorlist.org>
Sent: Sunday, October 16, 2011 5:38 PM
Subject: VECTOR: Vcc buss rails being pulled down.

> I'm working on a Slot machine MPU, with
> similar 74xxx components like our arcade
> games.
>
> The Vcc buss is being pulled down to about 50mv.
> The LM340T5 runs very warm, so were keeping the
> power on time very low.
>
>
> Besides removing the IC's one at a time (and
> of course their not socketed ) is there a way
> to ID which component is at fault ?
>
> We've removed the IC's that are socketed, and
> checked for warm or hot components.
>
>
> Todd
>
>
>
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Received on Sun Oct 16 18:33:52 2011