From: Robert Baer
X-Mailer: Mozilla 4.75 [en] (Win98; U)
Subject: Re: spurious oscillations
Date: Sat, 21 Sep 2002 07:31:53 GMT
NNTP-Posting-Date: Sat, 21 Sep 2002 00:31:53 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
Gabriel Horner wrote:
> I'm trying to repair a pulse generator which for now only oscillates at
> 10 MHz. I've verified that the spikes which trigger the pulses are correctly
> made when I vary the frequency knob but I've also discovered a 500 mV
> peak to peak 10 MHz oscillation. As I trace the signal down further, the
> spikes die away and the generator ends up triggering on these
> oscillations. The whole problematic section is composed of transistors and
> includes a Schmitt trigger. Any ideas on how to find the troublemaker if
> my diagnosis is right?
Nominally speaking, a pulse generator does not oscillate.
I would suggest that you get a schematic or make one, so you have
something to follow.
Look at the method of generating the pulse: (1) dump energy into a
delay line (which determines max width) and another switch turns it off;
(2) turn on and then of the output driver, (3) ??.
Start at the beginning and go stage by stage; look for bad capacitors,
burnt or cracked resistors, bad transistors.
Try to figure out if something else went bad and that part was thereby
destroyed so the cause gets fixed, not the symptom (ie: do *not* work
like a doctor).