[Test-Equipment] 71 ohm ceramic disk capacitor

[Richard Knoppow]

----- Original Message ----- 
From: "Lee" <farmer3209 at tampabay.rr.com>
To: <test-equipment at mailman.qth.net>
Sent: Monday, December 28, 2009 3:42 PM
Subject: [Test-Equipment] 71 ohm ceramic disk capacitor


Gentlemen, after spending 6 1/2 hours in an HP Spectrum 
Analyzer I narrowed
it down to the AGC circuit. Then found an A14 line tied to 
that circuit by
an isolation diode that goes to 3 other boards was ­1.7volts 
instead of 7.7
volts, pulled parts along that line and found a ceramic disk 
capacitor
marked as a 220pf that read 71 ohms on the Fluke DMM. 
Replaced it, and
suddenly had a working machine again. That was a very 
expensive disk
capacitor.. The unit then passed all performance tests which 
required
another 2 hours to complete.

Conclusion: don¹t get caught up looking at op amps and A-D 
converters
forgetting about the simple things.

Lee

    There is a myth that ceramic caps don't fail. I've found 
a lot of bad ones. Also silver micas, which are among the 
most reliable parts. When this stuff gets old enough 
anything will fail.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com