November 2017 14:08
To: 'Discussion of precise voltage measurement'
Subject: Re: [volt-nuts] 3420B chopper drive problem
Interestingly the PCB is marked to suggest the schematic is correct! And while
the connections to the neons have been reworked, it would appear the diodes
never have.
Reversing
: [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
Another probable error in the manual, on page 5-8 (80), diagram, which
shows the monitoring of the neon currents:
That diagram is ok for the A-version, as both neon currents are measured
with the same polarity in its oscillator circuit.
The B-version anyhow should look different, as the
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
I'm trying to resurrect a 3420B.
I'm looking at the waveform at TP1 on the A2 board. This is supposed to be
a square(ish) wave, but within a 6mS period, there should be two cycles of
the signal, one with an amplitude of (say) 150mV, and the next cycle only
100mV. I think that the larger
