[XCSSA] Blowing Fuses and Unsure Why

[X-otic Computer Systems of San Antonio]

Unless there is a short on your board (and it would cause the fuse to blow 
instantly) and assuming that there are no shorted caps (which would also 
instantly blow the fuse), then the most likely culprit is the regulator. 
Make sure it is wired in correctly and make sure the board was laid out 
correctly. 

I would start by removing the regulator and applying power.  If the fuse 
still pops, then it is obvious that there is a short elsewhere.  If the 
fuse does not pop, then I would go over each trace with a meter set to 
audible continuity tester mode.  I would also test the regulator outside 
of the board to make sure it is still good (chances are that it may be 
bad). 

As far as the fuse is concerned, you can always go to Altex or Ratshack 
and get any 500ma fuse (get several), you may also want to consider 
getting a cheap matching fuse holder.  If you don't get the fuse holder, 
then solder wires to the fuse and solder the other end of the wires to the 
board.  Your best bet is to get a cheap matching fuse holder and solder it 
to the board and then you will be able to change out the fuse when it 
blows.  If you are really in a bind, then I would use the 30 gauge wire as 
a temp fuse.  The wrapping the 30 gauge wire around the fuse just makes it 
easy to replace the temporary "fuse" when it blows! 

As a general rule of thumb, once the second fuse blows, you probably need 
to take out the meter and start checking stuff out before attempting to 
apply power your circuit again.

Have fun!

Charles S.



From:
X-otic Computer Systems of San Antonio <xcssa at xcssa.org>
To:
xcssa at xcssa.org
Date:
01/09/2009 07:03 AM
Subject:
Re: [XCSSA] Blowing Fuses and Unsure Why
Sent by:
xcssa-bounces at xcssa.org



No I didn't get a chance to work on it yesterday (the e-mail that was 
sent late last night was the same one I sent that you read). Plan on 
doing that this weekend, though. Can you elaborate on the wire-wrap? I 
can use that as a fuse?


On Jan 9, 2009, at 5:53 AM, X-otic Computer Systems of San Antonio 
wrote:

>> the 9VDC lights up for a few seconds and then my
> fuse blows.
>> Everything looks connected properly but there is no
> load on
>> either side except for the  LEDs. I'm thinking it
> has something
>> to do with grounding. I haven't connected the
> grounds on either
>> side and I'm guessing that might be my problem? If
> so, does it
>> matter where I connect the grounds together?
>
>  No, it does not matter !
>
>  Did you split it, like I suggested yesterday?  If
> you did, was
>  it the input side (to the 9V regulator)or the
> output side?
>  Sounds it's the output side. and more importantly,
> you're blow-
>  ing a .5A fuse, that's a lot of current.  Your LED
> as shown only
>  draws .023A (23mA) and the amount of turn on filter
> surge is
>  nominal.
>
>  Something, besides the LED & R2 is drawing in
> excess of 477mA!
>
>> Unfortunately, I ran out of pico fuses.
>
>  For trouble shooting, if you have any 30gauge wire
> wrap wire you
>  could use that for trouble shooting the problem.
>
>  Try disconnecting the LED (LED2) and see if it
> still blows the
>  fuse or 30gauge wire.
>
>  Too bad I'm a Hill Country hermit, I could find/fix
> it in a few
>  minutes.
>
> Lou
>
>
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