This is my first real post, so I hope I get the formatting right...
I am also not quite sure if Test Equipment or Repairs is the right topic, but since it is not realy a repair I chose Test Equipment.
A few weeks ago I got myself my first bit of vintage test gear, namely a Keithley 171 DMM from the early 70s. Since I could not find a thread about it in the forum I thought I make some photos and share my experiences.
I got it from Ebay for about 80€. It was described as "turns on and the display is working". When it arrived I couldn't get it to measure anything, so I got it open and had a look around:
The culprit was a blown input fuse, which was sandwiched between the analog circuitry board and the range switch board:
After replacing it with a new one i got the DC voltage, ampere and ohm ranges working, but no luck with the AC ranges.
The manual mentions (see
https://download.tek.com/manual/171(Model171_Multimeter).pdf) states that both AC ranges use the same AC/DC converter circuit before the signal goes in the common siginal path (see PDF p.17).
An impedance transforming JFET (TO-72 2N4220) is right at the beginning of the circuitry (PDF p.84), which I suspect to be dead.
Unfortunately it is on the range switch board, right under the range switch, which is soldered down and blocks any attempt to measure it in circuit. Q1101 is the Can right in the middle of the picture above the lowest bar:
I tried to get the range selection board out of the unit, but I already fail at the knob on the front panel, which is screwed in with what I think is a weird imperial hex screw for which I do not have a fitting bit (1.5mm slips, 2mm is to big)
But since I will anyway only use the DC and Ohm range it is not so big of a problem.
Last but not least a shot of the Nixie tube display, which uses NL-841s from National Electronics. I can not compare them to other Nixies, but I think they are in a pretty good shape for their age:
Component wise the DMM is full of carbon film resistors which could become a problem in the future. The electrolytic capacitors look good but have no vents. I am not sure if they are solid ones, or they just did not have vents back in the 70s?
I hope you enjoyed my little post.
Edit: Didn't quite get the images right, without having them to large, so i leave them at the end for better readability.