[volt-nuts] 3420B chopper drive problem

[David C. Partridge]

Well that would explain a lot!  Both diodes are wired with the cathode to the neon!  

Does it matter which one I reverse?

Dave

-----Original Message-----
From: volt-nuts [mailto:volt-nuts-bounces at febo.com] On Behalf Of Dr. Frank
Sent: 07 November 2017 16:32
To: volt-nuts at febo.com
Subject: [volt-nuts] 3420B chopper drive problem

Hello Dave,

in the schematic, the polarity of the diodes in series with the neon bulbs is definitely wrong.

If you compare with the 3420A on page 7-7 (29), but also with the Fluke
845 which is similar, both neons have to be switched at 180°.

Maybe someone else has erroneously reversed one of the diodes in your unit before?

If both neons are really firing in phase, instead, that could explain this non-symmetric waveform, which you observe.

Frank

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