RE: Zener diode check

---------

From: Nick Kennedy (nkennedy@tcainternet.com)
Date: Sat Aug 24 2002 - 07:48:08 CDT


-----Original Message-----
From: TC Dufresne [SMTP:tdufresne@neb.rr.com]
Diodes? Well now, here's the deal. It uses a 12v 1 amp zener diode in the
amp section. (1N4742)
When I check that with my handy dandy Radio Shack multi-meter (*with diode
checker) I get ,667 (?units??) and I reverse the probes, I get .831
(?units??) I thought I was supposed to get a number like the first for the
one position of probes, and when ya reversed the probes, I was supposed to
get a <blinking> <blinking> 1.0000 thing..(infinity)
Am I wrong? Could the zener be "bad"? Could it be that simple?

***********

Could be. But I'll bet you're reading through other things in the circuit.
 That zener is probably connected from collector to ground of the final
transistor. With + probe at ground and - at the collector, you read
forward through the zener: 0.667 volts. In the other direction, you should
read "high", but you are also reading everything in the rig that goes from
the + supply line to ground.

I'm not a big fan of in-circuit component testing, not that I'm a great
troubleshooter or anything. Probably the best it would do would be to show
shorts or opens. I guess you've already gone over the board with a
magnifier looking for bridges and bad solder joints. Toroids with wire not
stripped fully. Have you decided that it's the final amplifier stage? Can
you hear the oscillator in your receiver? Tracing RF signals might be
tricky if you're not equipped for it, but checking DC operating voltages
might be a good simple check. It's usually easy to dope out what they
should be, except for the final (class C) amplifier.

72 & Good Luck,

Nick, WA5BDU


Search QRP-L Archives

[ QRP-L Archive | ]
[ 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 | 2001 | 2002 ]

---------

This archive was generated by hypermail 2b29 on Sun Oct 13 2002 - 10:39:48 CDT

kd4ab@kd4ab.org