[volt-nuts] Making a Reference IC

[Dave M]

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 <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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Dave M