Hello Ken,
If I understand this correctly, R6 adjustment produces a few millivolts
change at U1 output but no change at all at the power amp output. That
seems to point to the input differential stage or the current to voltage
converter stage following that. This will be difficult to find without
removing the board from the machine. Given the amount of time you have
spent so far it would be quicker to rig up enough extension leads to
operate the board outside on the bench. I've done this many times when
making or obtaining extender boards was impossible.
Regards
On 11/07/14 14:27, Kgoodhew wrote:
Hi Gerd,
C8 is on the drain of Q38 the Fet just near the input to the A7 amplifier,
according to Charles it is switched in parallel with C1 on the source of Q38
to vary the integration time.
Using the cro on dc to look at the output I get 15mv dc on the output and I
cannot vary it by R6.
Will do some further checking today.
Ken.
Message: 5
Date: Fri, 11 Jul 2014 12:38:05 +1000
From: Gerd <[email protected]>
To: Discussion of precise voltage measurement <[email protected]>
Subject: [volt-nuts] fluke 5200a repair
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hello Ken,
Which board are you looking at? On the amplifier board (A7) C24 is the
input cap. Where is C8?
Don't rely on the multimeter to filter out the AC on the DC ranges, it's
best to use a CRO. How is the signal coming into the amplifier from the
oscillator? If the input to the amplifier is disconnected, is the offset
still there?
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