[volt-nuts] A Fluke 732A: Return it or keep it?

[Bill Gold]

Michael,

Just a side note here on adjusting the 3 calibration pots inside the front
panel of the 732A

Fluke did supply an adjustment tool with each 732A but I don't know exactly
who made it or what model number.  I use a General Cement ( GC ) model 8276
adjustment tool, the end with the blade recessed, to do the job.  Sometimes
it takes a little fiddling and patience to get the adjustment tool to engage
the slot in the pot, but it can be done and without any danger of shorting
something out.
http://www.alliedelec.com/search/productdetail.aspx?SKU=70159521

360 uvolts ( 36 ppm ) above 10 volts seems more than a little high for one
of these units.  The worst I have seen over 6 units is around 120 uvolts (
12 ppm ) out of spec, but I was able to bring it in by changing the jumpers
on the A7 board.  It is conceivable that someone totally screwed up the last
calibration.  You would need to take off the top cover, the top guard cover,
remove the top foam piece and take a look at the jumpers on the A7 board.
The one thing I can't remember right now is if shorting the resistors R12
through R17 on the A5 board, by adding or removing jumpers on the A7 board
lowers or raises the output voltage at 10 volts.  But in the manual I did
find an addendum to paragraph 4-38 which says.

"Cutting a jumper increases the 732A 10 V output the amount labeled above
the jumper.  Likewise, completing a jumper decreases the output the amount
of the jumper label".

So that should help you once you view the jumpers on the A7 board.  I do
know that you can add or remove multiple jumpers on the A7 board so the
total range of the change in the 10 V output can be around 750 uvolts ( 75
ppm ).  If you see many jumpers on the A7 board this would mean that someone
tried to lower the output voltage and that the reference could not be
adjusted properly to exactly 10 V.  In other words if you see no jumpers on
the A7 board then you could possibly bring the output to exactly 10 V from
it's present ( presumed ) 36 ppm too high.  You really need a "standard" 10
volts before you do this.  But since the seller's DVM is reading 40 ppm too
high and your 3457A is reading 36 ppm too high then the output of the 732A
is probably also high.

What part of the country are you located in?  Maybe one of the many "Volt
Nuts" lives close to you can give you an idea of what 10 Volts really is.

Also I have seen batteries that are so old and messed up that the "Charging"
light will never come on.  The internal resistance is so high that the
charging circuit simply doesn't work.  Your thermistor value and stability
seems very good so it looks like the oven temperature control circuits are
working correctly.

I hope the above helps you in determining if you keep the unit or send it
back.

Bill

----- Original Message ----- 
From: "J. L. Trantham" <jltran at att.net>
To: "'Michael Hong'" <mikeyahee at yahoo.com>; "'Discussion of precise voltage
measurement'" <volt-nuts at febo.com>
Sent: Friday, March 07, 2014 5:57 PM
Subject: Re: [volt-nuts] A Fluke 732A: Return it or keep it?


Michael,


The schematic of the A5 Reference PCB Assembly shows the calibration
adjustments and the drawing of that assembly shows the location of the
adjustments.  They are deep inside the unit.  You'll need a small flat
bladed tool, a flashlight, and probably a magnifier.  I used a length of 12
ga. copper wire with one end flattened to make a screwdriver.

Good luck.

Joe

-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
Behalf Of Michael Hong
Sent: Friday, March 07, 2014 6:19 PM
To: volt-nuts at febo.com
Subject: [volt-nuts] A Fluke 732A: Return it or keep it?


(3)
Front panel calibration hole
I put a thin flat blade driver into the holes. I couldn't feel anything
until 4 1/4" inside where I felt something but not the potentiometer.



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