[Test-Equipment] 71 ohm ceramic disk capacitor

[Howie]

Was that cap a pretty high-voltage cap?

I had one in a scope that gave me fits CUZ it was a 1600volt jobbie-do.

I thought,"no way that was it as the voltage is supposed to never get above 
200 in the circuit."

After scratching my head,(dangerous to do if you only have a few left on 
top,HI,HI!),I checked it and it had no reading whatsoever,no 
resistance,(short),no esr reading at all,no capacitance,not even a 
picofarad!.

Replacing gave the scope back.

So I looked at schematic and that cap was on the external input line,but I 
had not used that line at all.
Then I remembered my "buddy"" had borrowed it  a week before.Aha,the 
culprit!


----- Original Message ----- 
From: "Lee" <farmer3209 at tampabay.rr.com>
To: <test-equipment at mailman.qth.net>
Sent: Monday, December 28, 2009 6:42 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
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