Electronics > Metrology

HP 34401A hacks and upgrades

(1/11) > >>

cellularmitosis:
I thought I'd start a thread for hacking on the 34401A, as a "hacked" 34401A seems to be one of the next-best options for volt-nuts who aren't (yet) willing to fork over the cash for a 3458A.   :-DMM

I'll kick us off with this one:

I believe I've just confirmed that you can substitute whatever 7V Vref you'd like in place of the LM399.  This means an LTZ1000 upgrade should be possible.  :-+  (or paralleled LM399's for lower noise)

The core of the 34401A Vref is a bootstrapped LM399 (see attached).

I removed R409, unplugged the LM399 (U403) (it is socketed! :wtf:), and plugged an MV106 into the zener pins of the LM399 socket.  I was able to move the ADC reading around by changing the dials on the MV106.

Note that there is a leg of resistors hanging off of +Vz (a voltage divider which forms a 5V ref: R441 and R442), which total to about 50k, so your 7V ref will need to supply about 140uA.

cellularmitosis:
(pics)

cellularmitosis:
I wonder if the decision to socket the LM399 was so that they didn't throw away any pre-ageing by soldering in the LM399.

rhb:

--- Quote from: cellularmitosis on April 26, 2018, 12:53:11 am ---I wonder if the decision to socket the LM399 was so that they didn't throw away any pre-ageing by soldering in the LM399.

--- End quote ---

In which case, why not a crimp?

cellularmitosis:

--- Quote from: rhb on April 26, 2018, 01:03:05 am ---
--- Quote from: cellularmitosis on April 26, 2018, 12:53:11 am ---I wonder if the decision to socket the LM399 was so that they didn't throw away any pre-ageing by soldering in the LM399.

--- End quote ---

In which case, why not a crimp?

--- End quote ---

Good question.

I have noticed that the selected zeners (1N829A) in EDC gear are soldered in place, which is an interesting counter-point.

Navigation

[0] Message Index

[#] Next page