[volt-nuts] Fluke 732a concernes

[acbern at gmx.de]

Igor,

I would actually ignore the 1V and 1.018V outputs. You can always determine their actual value using your 3458A in transfer mode against the 10V. The purpose of a voltage reference is not to be at exactly the nominal value all the time (requiring readjustment), but just to be close to nominal with known deviation and known drift rates. Working 732As show a very low drift, well below spec, provided you do not do much adjustment (never adjust the trimmers). Users have seen massive drifts starting when this was done. My 732A e.g. has a drift of only about 0.2ppm pa over a couple of years, so pretty good. The drift direction may change when you let it cool down, so you dont want to switch it off.

cheers



> Gesendet: Dienstag, 29. August 2017 um 07:27 Uhr
> Von: Igor <iobh at hotmail.com>
> An: "volt-nuts at febo.com" <volt-nuts at febo.com>
> Betreff: [volt-nuts] Fluke 732a concernes
>
> Hello,
> 
> I am Igor and I am new to this forum. I have a Keithley 2002 and 3458A.
> 
> As probably a prerequisite for this list, I recently acquired a Fluke 732a and checking it our now. I do not have any history for the unit and it was shipped to me cold without batteries and with broken battery carrier.
> 
> After a warm up 10V read about 7ppm high and 1.018V read about 13ppm high. This is probably ok for a very old unit like this.  However 1V read 116ppm high! Is this typical? Would it be a sign of internal resistor drift?
> 
> I had to move an internal jumper for 5ppm adjustment and then adjusted 10V and 1.018V to proper value using a calibrated meter. I do not see any way I can adjust 1V output to be even close to spec. Is opening the oven and adjusting resistors an option? Should I just leave it alone and monitor drift?
> 
> When fully warmed up the thermistor measured 3.662KOhm. Is this a typical performance?
> 
> Additionally when inspecting the unit in more details I found a burned PCB patch on A4 Regulator board, right under R12 and R13 resistors in proximity to transistor Q4 and capacitor c8. It is literally burned to black crisp. The resistors themselves appear ok. Maybe they had been changed after the board burned.
> 
> When running the board I get transistor Q4 as hot as 220F, still below its 150C max running temperature. The PCB board and resistors get to 180F. Is this normal, or should I be concerned?
> 
> 
> Thank you very much.
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