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 <admin@controlelectronics.com.au> To: Discussion of precise voltage measurement <volt-nuts@febo.com> Subject: [volt-nuts] fluke 5200a repair Message-ID: <53BF4E0D.9030808@controlelectronics.com.au> 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? --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com

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 <admin@controlelectronics.com.au> > To: Discussion of precise voltage measurement <volt-nuts@febo.com> > Subject: [volt-nuts] fluke 5200a repair > Message-ID: <53BF4E0D.9030808@controlelectronics.com.au> > 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? > > > > --- > This email is free from viruses and malware because avast! Antivirus protection is active. > http://www.avast.com > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > -- sig.html *Control Electronics Pty Ltd* The home of Shiftmaster Quality used test equipment *Phone*: 02 9456 0736 *Website*: www.controlelectronics.com.au <http://www.controlelectronics.com.au/>* Email*: admin@controlelectronics.com.au <mailto:admin@controlelectronics.com.au> ABN 86 109 858 022 ------------------------------------------------------------------------ The email addresses in this message are not to be added to any database, list, or mailing list without my prior explicit written permission. This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. Please note that any views or opinions presented in this email are solely those of the author and do not necessarily represent those of the company. Finally, the recipient should check this email and any attachments for the presence of viruses. The company accepts no liability for any damage caused by any virus transmitted by this email.