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

[Jean-Pierre Desrochers]

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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>>
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