[volt-nuts] 7081 calibration "Zero too large"

[David C. Partridge]

And just to annoy me, half way through checking the circuit, after taking voltage and signal readings off a good 7081, it all started behaving normally.  I *hate* it when faults go and hide like that when you are trying to hunt them down!!!  

Maybe a capacitor that had gone leaky had re-formed?

Dave
-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On Behalf Of David C. Partridge
Sent: 03 May 2012 03:09
To: 'Discussion of precise voltage measurement'
Subject: Re: [volt-nuts] 7081 calibration "Zero too large"

It looks like the fault is in the input amplifier which is logically part of the DC ranging circuit.  The error seems to appear at the output of IC402.  Did anyone find the patent for this circuit - it is actually quite a complex circuit surrounding an LM343 with a discrete chopping arrangement using FETs an OP05 and LH0052 all of which I think is there to cancel the offset of IC402.

Dave