Hickok 1890M in-circuit transistor tester (1965 portable military unit)

[trobbins]

I'm getting ready to go through a calibration of a Hickok 1890M transistor tester using the Technical Manual.

A preliminary check years ago identified some slight stiction in the meter, which I have just attempted to remove and appears ok now.  The meter was hermetically sealed, and required some effort to access - and that now doesn't allow the original cover to be nicely cinched back on around the perimeter, but as it isn't doing any more military service then that won't matter.  The meter coil uses a single bearing for ruggedness, so I dropped in some IPA to the two end access slots in the hope that that may seep in and flush the internal bearing surface.  I also identified the rear hairspring had one turn out of place, which was easy to return to normal.  I can't detect any stiction now so here's hoping.

I also replaced the primary batteries with three external plug packs and an internal regulator board using LM317L regs to provide the three isolated battery taps/groups (0-22.5V; 0-3.0-4.5V; 0-1.5-3.0-4.5V).

One hurdle I'd like to jump is to get a full circuit schematic diagram if anyone has that.  The Tech Manual only has some abridged schematics related to a few circuit functions, and as this tester is a more advanced version of the Hickok 890 tester (which has an available schematic), the extra circuitry is a lot harder to track through all the extra switches, switch wafers, and parts.

Ciao, Tim