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Old Fluke Multimeters

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rsjsouza:
I found in my hard disk some older downloads where I got the schematics and component placements and it seems the capacitor in question is C28: 10µF/16V in parallel with the zener voltage reference VRZ.

Why this was removed is a mystery, but perhaps it was suitable for stability?

Rev 1


Rev 3



Unfortunately the full scans are too large to be attached, so I did a search on the manuals and found that Mr ModemHead was kind enough to scan his copies and make them available at:
https://www.eevblog.com/forum/testgear/fluke-8060a-calibration-service/msg1462267/#msg1462267
(obviously he also mentions the C28 mystery)

Electro Detective:

--- Quote from: ModemHead on March 26, 2018, 12:38:58 pm ---
...C28 is a 10uF across the 1.2V bandgap reference.  To be honest, I hadn't noticed that it disappeared at some point in the lifespan of the design.  I have hardcopy documentation from 1983 and 1988. 
C28 exists in the 1983 rev, but is not mentioned in the 1988 and the much-later PDFs available on-line from the Fluke archives.

If it is not in your meter then there should be no need to include it..


--- End quote ---

Let sleeping dawgs be for now,
well until more intel flows in..   ;D

IconicPCB:
Looking at the schematic the current for the zener is sourced via Z3 a 50K resistor.
It is possible electrolytic's leakage current may have been detrimental to the stability of the reference voltage.

I see no reason why a low leakage film capacitor could not be used there.

rsjsouza:
The issue there is space. If you want to keep the same 10uF that will take you to MLCC territory. How is leakage on these types of capacitors?

You could also derate its voltage for even less leakage (use 25V instead of 16V).

Edit: found some info at Murata, which places their MLCCs typically at 500MΩ-μF - this yields 50MΩ for a 10µF capacitor.

coromonadalix:
 fluke 8060a, the 40 pins main  ic could be an intersil 7106- 7107 series ??

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