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From: "Steven Murray"
Subject: Re: [Newbie]: Testing a +5V IC regulator
X-Newsreader: Microsoft Outlook Express 5.50.4920.2300
Date: Wed, 13 Nov 2002 10:07:55 +1100
NNTP-Posting-Date: Wed, 13 Nov 2002 10:05:12 EST
Organization: Pacific Internet (Australia)
"Alistair Campbell" wrote in message news:firstname.lastname@example.org...
> I am new to electronics so this is probably a silly question.
> I am building a kit parallel port interface. The power supply to the
> various IC's is via a 78L05 IC which produces 5v from 9v.
> When I test voltage to the supply pins on the IC's they rate at 9v
> when they should rate at 5v (+/-0.5v).
> Tracking this down I get 9v at the output pin for the 5v regualtor. I
> am using a multimeter and checking by connecting one probe to the
> output pin and one probe to the negative rail.
> Does this mean that the IC 5v regulator has failed? Or am I doing my
> testing wrong?
> Any thoughts would be much appreciated.
Check you have not got the regulator "Backwards"
That is - the input swopped with the output.
Also, check if the "Ground" pin on the regulator
is open circuit (ie, Unconnected). Both these
things can produce the symptom you describe.
Likely as not, when you correct the fault the 78L05
may still work. Then again, I have also seen this
fault with bad 78L05's, so there is a chance it is
faulty. The unknowns are what debugging is about.
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