Re: 2430A Repair - a first in many ways


Joerg
 

So I finally got my old Hameg repaired - another capacitor short, this time a ceramic, and could measure more on the 2430A.

I mainly checked the low DC voltages on the side board and they are all spot on with about 5mV p-p ripple. The only one that that is not within a view mV of specs is the 8V which measures as 7.85V, that that is still just 2% shy. So I'm very pleased. I also measured the 10MHz on the top board and that also looks super clean and at the right frequency.

Next, I was looking for a good voltage reference and the only one I had laying around was the bandgap in an LT1365 which is 200mV. On both channels, limited to 20MHz, taking 128 averages and at 10mV / div and 10ms / div it measures 20.000mV with a 1:10 Probe (no readout pin, but a P6133). That is pretty spectacular I thought, but it also worries me a bit, because my Fluke 8840A tells me its somewhere near 202 mV although that meter has not seen a calibration in a long, long time I think 1% of accuracy should always be there (my Fluke also checks out against my other multimeter ...). I measured on two specimen of the chip, same result. The initial accuracy of the reference in the chip is 200mV typical with 190-210 min/max.

So, I'm a bit skeptical of this reading. It just seems too good. What further makes me skeptical that the readings change with Volts/div in the single percent range (I can kinda see that, you're getting toward the low / high end of the range) and time / div (I can also see that - on shorter time scales there is less averaging going on).

What are your experiences when abusing the scope as a multi meter measuring DC voltages?

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