Tektronix 7854 Oscilloscope

Tektronix 7854

This is the 'scope and repair that began the collection. This is a legendary and famously expensive instrument, and the first scope capable of 10 GHz bandwidth that I ever saw and used early in my career at Bell Labs. The last great analog scope, but endowed with plenty of digital power. See it doing TDR (time domain reflectometry) with the 10 GHz head to locate a fault in our Apollo Guidance Computer memory module. Clicking on the picture or the link below will take you right where the action with the Tek 7854 starts:

https://youtu.be/uyxQmb2u6Hk?t=536

My vintage modular Tektronix 7854 oscilloscope quit on me for the second time. It's the scope I used to develop my MarcDuino electronics. It's a fabulous high end vintage scope, the last of the great analog Tek scopes. Now becoming a valuable collectible. Equipped with the 10 GHz sampling head plug-in (which I have!), and the TDR head (Time Domain Reflectometry). It was worth a fortune back then. The first 10G scope I ever played with. It even has digital memory, it can do waveform calculations, take single shots traces. Look at the million buttons! There is always one set the wrong way. A classic. It was my only scope until very recently.

Find a good overview of the 7854 mainframe in the TekWiki:

http://w140.com/tekwiki/wiki/7854

And a link to all series 7000 plug-ins

https://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_Test_Equipment.htm

The user manuals, service manuals and schematics documentation is here:

Manuals on plug-ins are here:

It weighs a ton. Inside it's a wonder of engineering, stuffed to the gills with analog electronics and board after board of simple digital logic. Amazingly enough, I could find the schematics on the web, which decided me to attempt a repair.

Aided by my modern oscilloscope, I was able to find the culprit, fortunately in the switching power supply circuitry which is easier to debug. A bad electrolytic capacitor. A classic failure mode of vintage equipment:

Rig a modern one in:

And lo and behold, it works again! Until the next capacitor lets go .