[volt-nuts] HP3458A voltage reference boards

[Will]

Mark Sims wrote:
> A while back I cam across a site that detailed using the HP3458A
> voltage reference board (which show up regularly on Ebay).  I can't
> find where I saw that info. Does anybody have this info?

I have been wondering where do the surplus reference boards "which
show up regularly on Ebay" come from. The sellers usual story that
they are ex military stock doesn't make sense, because it is probably
the most unlikely part of the whole meter to fail. And the aging is
opposite to everything else, it only gets better.

One alternative is that they are rejected by the HP factory. I don't
have any idea of the real percentage but 10% rejection rate seems very
low when we think about the high requirements.

Any meaningful testing of the LTZ1000 requires the surrounding
components. The op-amp and resistors may be expensive to us but only a
few dollars in large quantities HP buys them. And even if it would be
possible to test the chip alone, they would need to repeat the test
after the board assembly because there can be a problem with the other
components or even the board itself. So they probably test fully
assembled boards rather than individual components.

The last time 3458A reference boards were available on Ebay the seller
provided individual photos of each board instead of a generic photo. I
noticed that the boards were missing the type number sticker and
quality control marking usually found on the units inside a 3458A.

Anyone bought / tested them?


Will