Re: 11801 NVRAM

be_moulton
 

Noob to the group. I had wondered IF NVRAM data was lost if that actually did remove factory enhanced time interpolation calibration data, I recall vague reference to that in one of the manuals ? I have some equally broken CSA803a and 11801b and haven't taken the plunge to attempt fix yet.

I see the post about the apparent shift in frequency measured changing from known 100KHz to unexpected 106KHz upon losing the NV data. So sounds like it may be true regarding special factory time interpolation cal constants. So, how to restore?

My very limited understanding of the CSA803/11801s is that the 200KHz sampling rate has a tiny time interval added each 200KHz sample so that each subsequent sample taken is shifted very slightly in time to be in a different spot on the repetitive waveform so that an entire cycle of the repetitive waveform can be reassembled from the 512 samples taken. For the measured frequency of the reassembled waveform is to be accurate, then that added time interval to each 200KHz sample must be a very accurate delta time interval as it is dictating the effective sampling rate. So, if the missing factory calibration constants are adjusting that added delta time interval for each subsequent sample, then the DEFAULT "time interpolation" constants following NVram recovery may corrupt the effective time sampling and the calculated frequency of the reassembled effective time sampled waveform. So, if those 32 calibration numbers could be adjusted while monitoring a known precision frequency sinewave, then I wonder if it's possible to see the sampled waveform begin falling into place as the expected sinewave as the cal constants approach a better time interpolation? The challenge would be how to iteratively adjust the NVram constants without removing the NVram chips a thousand times. I don't know of any GPIB way to SET the value of each NVram cal constant, maybe there's some tribal knowledge regarding that ??

Lacking any external wisdom, I may also spend some time bashing my brain against the blue/green mystery machine to attempt restoring a decent calibration. I'm betting somebody knows a trick to do this.

Best of luck.

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