The original reference has a shorted Zener. I verified that with a curve
tracer (that was a couple years ago, but I remember it well.
I saw the post from Hank, and have emailed him about the 732A stuff that he
has.
I think my easiest and least expensive approach to getting this instrument
back on the bench is to build a circuit with an LM399A and fix it onto the
731B reference board.
Cheers,
Dave M
Todd Micallef wrote:
Dave,
What is the problem with the original reference? I have not heard of
too many failing. There was also a reply from Hank on another
message. Perhaps he can provide the needed parts from a 732A?
Todd
On Mon, Sep 14, 2015 at 6:45 PM, Dave M <[email protected]>
wrote:
After making a mess in my garage while searching for it, it turns
out that that my Fluke is a 731B. It appears to use the same
Voltage Reference IC as the 731A, so no big deal there.
I found a previous discussion about the 731/732 reference ICs.
Seems that the ICs are either from Motorola
(MCA1914/MCA1924/MCA1934) or GE (RA3). Doubtful that GE continued
production of that IC very long, so my guess is that these are
Motorola parts. It's all moot, since none of the parts are still in
production. I'm afraid to contact Fluke for a quote on the
IC/Resistor set. Don't think my heart could stand the shock.
I'd really like to get this unit back in operation, but I don't want
to break my bank account to do it. I have a few LM399s on the
shelf, so I guess that will be my best approach to a repair.
Thanks for the discussion,
Dave M
M K wrote:
On 12/09/2015 23:12, Dave M wrote:
I realize that better references are available.
I was thinking of resurrecting a long-defunct Fluke 731 that I have
in the garage. The reference IC is bad in it, and (1) I don't want
to throw it away without a meager attempt at repair, and (2) I
don't want to spend a lot of money on it because it's in pretty bad
physical condition.
I was hoping that someone could lend a touch of advice on those old
references. I have a few 1N827A reference zeners, and a washtubful
of transistors. Maybe something could be cobbled together that
would get the 731 back in operation. Maybe not to original specs,
but close, which is better than nothing.
Thanks for your reply,
Dave M
Jack Mcmullen via volt-nuts wrote:
Just thinking why would you reinvent a transistor/zener reference
when the industry's voltage reference chips are in the $2.00 or
less single quanities with performance far exceeding anything
previously available in discrete components??
-----Original Message-----
From: Dave M <[email protected]>
To: FEBO Volt-Nuts <[email protected]>
Sent: Sat, Sep 12, 2015 1:58 pm
Subject: [volt-nuts] Making a Reference IC
I was looking at the schematics for the Fluke 731 and 732 voltage
references. these, and several other brands and models of voltage
references, use the same or similar reference ICs as their basis.
The reference ICs are a Zener/NPN transistor pair on a single
substrate. Please view in a fixed-width font such
as Courier.
|
|
C |
|
|
|
|----
| B
/|
/ |
E |
|
+---------------
|
/------/
/
------
|
|
Just thinking... would it be possible to make a reference with
similar characteristics with discrete components (a low tempco
Zener and a transistor)? They would likely have to be closely
coupled thermally and
maintained at a constant temperature within an oven or by a
peltier device.
What criteria would apply to the selection of the parts?
Dave M
There has been some of those references available second hand from
ebay, mostly pulled, but some may be counterfeit, so look for
sellers with pictures showing it as old.
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government fears the people, there is liberty -- Thomas Jefferson
Dave M
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