[volt-nuts] Fluke 5200a

[John Phillips]

The problem is dc offset.


On Mon, Jul 7, 2014 at 5:30 PM, Gerd <admin at controlelectronics.com.au>
wrote:

> Hello Ken,
>
> From what I remember of this circuit, R26 is for output stage bias. R6 is
> for adjusting offset. By the way, which voltages are high and how much?
>
> The 5200 is an old beast, expect a lot of marginal electrolytics, carbon
> resistors that have drifted well out of tolerance and even transistors that
> no longer perform any where near what they originally did.
>
> Regards
>
>
> On 07/07/14 14:56, Ken Goodhew1 wrote:
>
>> Hi all,
>>
>>                  I am currently repairing a Fluke 5200a ac voltage
>> calibrator.
>>
>> After pulling cards in and out and soldering multiple wires on to test I
>> now
>> have the unit working about 98%.
>>
>> Anybody might have or know of where I might be able to obtain an extender
>> card for this unit as it would make it a lot easier to fix the last
>> remaining problem that I have, ie:- I have a dc offset voltage on the
>> output
>> of about 1mv when it should be +/- 100 microvolts.
>>
>> I am unable to adjust this with r26 adjustment on the power amplifier
>> board
>> as described in the manual. I have followed the troubleshooting guides as
>> per the manual, as well as testing just about all the components around
>> that
>> particular part of the circuit.
>>
>> The problem appears to be that the input stage is not being turned on hard
>> enough as all the suggested voltages for the input stage (Q1-2-3-4-5-9)
>> are
>> all too high. The supply voltages are all within spec.
>>
>> Anybody can offer suggestions?
>>
>> Sorry to put this out there in this group but I cannot find an online
>> group
>> related to fluke test equipment to ask.
>>
>> Ken Goodhew.
>>
>>
>>
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-- 
John Phillips