HP 4328A MilliOhmmeter - an easy restore back into service

[precaud]

Some of you may remember in 2002-03 in the runup to the Iraq war, there was a huge dumping of test equipment after the Pentagon gave the big DOD contractors the green light to upgrade their equipment cost-no-object in preparation for it. This unit was one of numerous pieces I bought at that time for next to nothing, found it needed a special cable, and set aside. And forgot about... until last week.

First step was to make a cable so I can test it. There are already a couple good articles on the 4328A, this one was particularly helpful with details on making the cable:
http://www.qsl.net/n9zia/hp4328a/index.html
Digikey still stocks the Hirose connector. There are cautions in the manual about the maximum resistance AND length of the cable if you want to use the meter on the 1mOhm range. The cable's resistance range is given as 2mOhm to 20mOhm per lead. I interpreted "length" as referring to a maximum inductance, though they never gave figures for it. The qsl article didn't address this aspect and used 22ga wire for their cable, which would easily exceed the maximum R limit on an 18-inch cable. I decided to make a cable using multiple conductors in parallel per lead to lower the inductance. I found an old video cable that has 9 pairs with fine-gauge wire and braided shield. It was nice and slinky too. Giving each pin 4 wires, the R for the 18" run was 21mOhm, just above 20mOhm limit. I didn't measure the inductance.

First test showed the unit worked but readings were all over the place, the range switch was badly intermittent. I doused the three switch decks with DeOxIt and worked the switch for a minute or so, and then sprayed it down with contact cleaner and air-dried it. Voila. That's all it took. Cal looked at tad high on all ranges so I went through the cal procedures which are very simple.

Comparing various resistors from 3mOhm to 100 Ohms, against a Valhalla 4716 and my HP 4276A used in Z/phase mode, the little Kelvin clips are a bit fiddly to use but once good contact is made, the 4328A gave identical readings as other the two meters. Not bad for a 40-year-old design.

Of great interest to me was to see if or how well it performed on the 1 milliOhm range with these low-inductance cables. I compared readings using three of the shorting "bars" that I use to short various fixtures or probes (see the 3rd pic). The next three pics shows the 4328A measuring them, easily showing the difference between them. Taking care to put the Kelvin clips in the same location for each, the measurements agree really well with the Valhalla.

I don't care for these little Kelvin clips. I like the size (about 2" long) but the jaws are barely textured and don't grab onto the DUT very well. Any suggestions on better small Kelvin clips?

This meter is a really welcome addition to the test bench.