[sdiy] How do you find the cause of a short ?

[Dan Snazelle]

That is a really cool/weird technique!!!

Ive never worked with a tapehead before, maybe ill try it!!!

Sent from my iPhone

On Sep 16, 2012, at 9:18 PM, nicolas <nicolas3141 at yahoo.com.au> wrote:

> One technique I have had recommended to me, but have not tried personally ...
> 
> Disconnect the +5V line or whatever line is shorted and instead feed it with an audio oscillator output - a pulse wave swinging 0-5V p-p would be appropriate in this case - would need to be capable of a reasonable current delivery, but not so much as to blow things up.  Then listen to the board with a tape head (or probably any other small pickup coil would work).  You should be able to hear where the main flow of current is going.
> 
> Nicolas
> 
> 
> ----- Original Message -----
> From: Jean-Pierre Desrochers <jpdesroc at oricom.ca>
> To: synth diy <synth-diy at dropmix.xs4all.nl>
> Cc: 
> Sent: Sunday, 16 September 2012 9:50 AM
> Subject: Re: [sdiy] How do you find the cause of a short ?
> 
> I repair lots of digital boards who have shorts 'somewhere' on the +5v supply line.
> The easiest way I found to pinpoint the actual shorting devices is this:
> Suppose the board you are testing is short somewhere in the +5vdc supplied circuitry,
> Just remove the local +5v supply and replace it with a variable 0-5vdc 5amp external lab supply.
> Start from 0v then raise the supply lets say to 3vdc. Check with your finger all the components
> for some that are getting HOT or warm (CMOS IC's). These are short most of the time.
> Beware, if tantalum caps are in the shorted parts team raise slower the VCC.
> This way I find at least 80% of the offending parts.
> JP
> 
> 
> ----- Original Message ----- From: "Dan Snazelle" <subjectivity at hotmail.com>
> To: "Steve Ridley" <spr at spridley.freeserve.co.uk>
> Cc: <synth-diy at dropmix.xs4all.nl>
> Sent: Saturday, September 15, 2012 5:21 PM
> Subject: Re: [sdiy] How do you find the cause of a short ?
> 
> 
>> That shounds like a great tool!
>> 
>> Sent from my iPhone
>> 
>> On Sep 15, 2012, at 5:00 PM, Steve Ridley <spr at spridley.freeserve.co.uk> wrote:
>> 
>>> 
>>> I got a (cheap second-hand) Polar Toneohm - it's a low resistance meter with a tone output
>>> whose frequency changes with resistance. Saves me a lot of unnecessary track cutting
>>> and component removal.
>>> 
>>> 
>>> Steve
>>> 
>>> 
>>>> I have a couple boards which are beeping on the continuity test between the positive rail and ground.
>>>> 
>>>> 
>>>> I cant find any bridged traces with a magnifying glass. Maybe a bypass cap blew? Or maybe......
>>>> 
>>>> But i have no idea how to figure out what might be the culprit.
>>>> 
>>>> I disconnected the power supply and the problem persists.
>>>> 
>>>> 
>>>> Thanks for any advice!!
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