Tektronix Analog Sampling

I’ve been putting this off for a while, but after a series of easy wins, I thought maybe I was up for the challenge. I have had in my possession for a number of years, a decent collection of analog sampling plugins and accessories from Tektronix, including 2 digital readout units, which allow for automated voltage and time measurements. Getting those readout units working is the goal, but first I have to start with a reliable sampling system.

I’m doing all this on a tektronix 568 mainframe, which has all the connectivity for the readout and automation systems, but these plugin pairs would work just as well on a 561 or 564 if you just wanted basic sampling functionality.

First I’d like to catalog the state of all of these plugins. I think the majority of them don’t work, so I want to find the units that work the most, and start from there. If I have a working pair, it will help evaluate the other plugins, as sometimes it’s hard to tell if the fault lies in the timing unit or the sampling unit.

The plugins

3S76 – Dual Sampling #2443
This one seems to work on the A channel. I have had it successfully send a trigger to the timing unit, and was able to position a signal on screen. The B channel is not working. After some time, I do get a sweep on screen for it, but I can’t position it. Getting the B channel working might be a good step in understanding how repair other sampling units. More on the repair below.

3T77 – Sweep #2810
This seems to work. Needs trigger sensitivity up pretty high, and it’s not what I’d call rock solid, but so far it seems like the best timing unit of the lot.

3T6 – Programmable Sweep #110543
This also seems to work well. External trigger provided on BNC J123 on the rear of the 568, via the gremar connector on the plugin

3T77 – Sweep #2250
Doesn’t work.

3T77 – Sweep #0881
Doesn’t work.

3T77 – Sweep #2246
Doesn’t work.

3S5 – Programmable Dual Sampling #40199
This seems to work on the A channel with the 1 known good S2 sampling head I have. The B channel is not working
Side note: the channels are lettered on these early sampling scopes, and numbered on traditional scopes. No idea why, but it holds true on the 661, and all of the 560 series plugins. On the 7S14, it’s back to numbers.

3S5 – Programmable Dual Sampling #30151
A channel works, with internal triggering. The B channel is not working.

3T2 – Random Sweep #30320
Doesn’t work.

3S76 – Dual Sampling #1209
Doesn’t work. With normal/invert switches set in the middle (a troubleshooting step in the manual). I get a sweep that can be moved vertically on Channel A, but not on Channel B, suggesting there are a few things wrong with this unit.
The sample diodes seemed to pass a multi-meter diode test, for what that’s worth.

Update: I stole a Nuvistor V1073 & transistor Q2163 from this to repair #2443

3S2 – Dual Sampling #40267
Both channels work, although I wasn’t able to get internal triggering working. Unfortunately I only seem to have one working sampling head at the moment.

3S76 troubleshooting

Set up with plug-in extender
Waveform at test point 4
Waveform at test point 6
Measuring bridge voltage on channel A – all good.
Measuring bridge voltage on B channel – no good
Sampling diode bridge