[volt-nuts] Making a Reference IC

[Todd Micallef]

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 <dgminala at mediacombb.net> 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 <dgminala at mediacombb.net>
>>>> To: FEBO Volt-Nuts <volt-nuts at febo.com>
>>>> 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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