Racal Dana 5900 Multimeter Teardown

Teardown of a modded Racal Dana high resolution digital multimeter, with a brief explanation of its working principles.

[chefchaudard]

13:10 the reference is actually the glass zener diode on the left of the little board. These diodes were aged several years by Dana before use, so to be as stable as possible.
18:20 There was an engineer in Racal Dana France, Loïc, who designed specific boards for bespoke requirements. The board, as you mention, was added to add some ranges for the external voltage reference input.
I have no idea why some customers required it, but it was popular. Military for some test bench, maybe? I remember fixing some non modified DVMs the customer tried to use with an improper voltage, overloading the input stage with devastating effects.

[bassobalalaikka]

very good teardown, especially the walking thru of different circuits schematics and workings.

[arnoldvanos]

As always read the manual before operating.The first option board mentioned, has nothing to do with special programming or a programming device. It is just straight forward, wired or TTl programming, with pull-up resistors. Further is it a standard BCD output, very basic TTl.
The modification you cleaned out is a Dana France modification. (See the sticker on the front) It has a switch on the front, to select between the normal 10VDC ratio input and a 33 1/3VAC ratio input. You did not have to remove anything. Just resolder the wires and fix the relay. Put the switch to 10VDC. The relay is not engaged and everything is working normal, like there is no modification. When the switch is on 33 1/3VAC, you just ad a true RMS converter, to the ratio input. This is a early version. Later came the 5940, which had a factory modification.
Questions? Just ask.
Danafan/The Netherlands

[PicaDelphon]

Made me do a Dust out on my DANA 5500 and after 50 year it still running better then the Crap other sell..