Products > Test Equipment
Hewlett Packard 740B DC Standard Digital Voltmeter (and 740A)
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beanflying:
Thanks, board by board pull and sort out coming up over the next few months so caps etc.

The Battery replacement is next on the list now the physical repairs are sorted that way I can hack a temporary output test box and run through the cal cycle as I go.
beanflying:
Just a few photos of Input cable unobtainium. If anyone has a couple of plugs in their junk bins Pat and I would love to hear from you  :-+

Deutsch MDR07-7P-090 is the number. HP for safety given the 1kV DC potential has pulled some of the pins on the input side.

beanflying:
Mercury cell replacement lashed up on the bread board tonight. 1.35xxx from 10-12v input. Resistors are low tempco Vishay's. Maxim 6341 csa for the 4.096 reference.

Will pop it on a board in the next day or two and add it to the 740b providing I am not struck down for adding an IC to a classic HP  >:D
beanflying:
Good enough for Australia  :-+

Just need to figure out where to mount the Mercury Battery replacement now. Temp is fairly stable here today and it hasn't moved a digit in over an hour.

edit yes I have now soldered the cap leg  :palm:

Running well on LiPo power at this stage. I need to sort out either a floating supply for the reference or figure out if the resistor divider network can be changed to allow a voltage compared to a circuit ground ..... The circuit diagram is a little interesting  :-/O
beanflying:
Must remember RTFM more carefully  |O

Seems there is actually two Mercury reference cells in the 740B.  :-- I did order two references so another to be made and crammed in here. Underneath the unit on board A11and under a guard cover hidden by wire and another board  is the loop gain check circuit  :-/O

Even with desoldering a coax that goes through the aluminium this is as far as the board moves.  :rant:
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