[time-nuts] SR620 fails in Self Calibration routine 07

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Oct 9 02:59:18 UTC 2008


Bruce Griffiths wrote:
> Jim Robbins wrote:
>   
>> My SR620 fails in its Self Calibration routine at "Cal Error 07".  The Users Manual describes this error as a problem with the "Start TAC" (Time to Amplitude Converters) and indicate that this flags a Hardware problem in the circuits which perform the analog interpolation between the 90 MHz clock ticks.  Anyone have any experience with this?  Is this a repair shop problem or user correctable?  I am unable to find a "Service Manual" for this unit also.  Many thanks for any input.  Jim Robbins
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>>   
>>     
> Jim
>
> The TAC is a fairly straight forward circuit comprising a capacitor that 
> is pre charged to a reference voltage and discharged at a constant 
> current during the short time interval to be measured.
> At the end of this time the voltage across the capacitor is measured by 
> an ADC which also measures the STOP TAC output among other things.
> Since it uses discrete components and the manual describes how it works 
> in some detail it should be fairly easy to troubleshoot the circuit even 
> without a schematic.
>
> Bruce
>   
According to the parts list the integrator capacitor used in the TAC is 
a 100pF Z5U unit.
If this is indeed correct then its no wonder linearisation of the TAC 
output is required.
However the sample and hold cap is sted to be polypropylene in the text 
whilst the parts list specifies polystyrene.

Bruce



More information about the time-nuts mailing list