[volt-nuts] Fluke 732a concernes

[Todd Micallef]

Igor,

Congratulations on your purchase. Your initial readings on the 10v and
1.018v did not appear too high. It depends on which jumpers were already
selected. I think on all of mine the 40ppm jumper was the only one
installed. The problem with the 1v output might be due to a broken trimmer
pot. I had a 10v pot that was adjusted past the ends and broken. I went
inside the oven and replaced it but it was difficult due to all the fine
enameled wire inside and the possibility for breaking one was high. The 1v
output is separately divided from the 1.018v so it is possible one of the
resistors has gone bad and replacing it would probably not be worth the
effort.

The thermistor value seems to be inline with my 732A except one. That
particular one is supposed to be 4k -5k ohms.

I don't know about the actual temperatures as I haven't measured any of
mine. The regulator board is full of carbon comp resistors. It is possible
that R13 failed, I have had some CC resistors fail with a much lower
resistance. R13 is supposed to be 2.7ohms. R12 is a WW at 0.39 ohms. I
would check both to see if they are still within spec.

There were some recent postings on EEVBlog concerning some recently
acquired 732A and tips on what to check.
I would recommend replacing that Schaffner input filter if you plan on
powering your 732A 24/7.

It could take some months of monitoring to determine how well it is
working. Beware that one reference may lead to more. A properly functioning
732A will have lower drift than your 2002 or 3458A so you will have to
measure it against other references.

BR,

Todd

On Tue, Aug 29, 2017 at 1:27 AM, Igor <iobh at hotmail.com> wrote:

> 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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