Archive for June, 2012

Tektronix 564B Scope Repair, Part 1

Sunday, June 17th, 2012

So, I have a real thing for old Tek scopes.

This is due in no small part to the gospel preached by Jim Williams (you can get the cliff notes for said polemic here as well as a lot of other great scope-related stuff and some repair notes).

More personally, it’s also due to the fact that my first scope was a Tek — a 454 that I snagged from trash pile at my college job before I knew an opamp from an opcode. I learned how to use a scope by fiddling with that thing, and I broke it a lot being a careless kid (mostly in shipping). This meant I had to fix it a lot, too. My first job out of school was repairing stereo receivers and guitar amps, and fixing that 454 was both alien and awesome. Alien, because it was way more complicated than a Fender Twin, and awesome because the service manual was head and shoulders above any repair treatise I’d ever seen, whether it was for a piece of electronics, a car, or a piece of software. It really wanted you to understand the instrument. I loved that manual.

So later, once I started drinking the Williams kool-aid, it didn’t take a whole lot of convincing that the old Teks were “intellectual integrity” reified. I won’t bore you all with the details — Jim did it better anyway (as does Kent at his excellent site).

Anyhow, I bought an old Tek564b off Ebay a long time ago and had it sitting in the project pile. I got it because I was fascinated by the idea of the Analog Storage Oscilloscope. In a nutshell, an ASO allows you to save a trace on the screen of an oscilloscope by using some special phosphors in the CRT and a set of special electron guns. You can save any number of traces (two is easy, any more and it gets tricky) to compare or photograph. Since the stored output is not sampled, it essentially has infinite “bit-depth”, and it was built at a time when semiconductor memory was still on the drawing board.

This particular 564 and its plugins had a few problems, but one really stood out as a great example of the interrelated-ness of systems inside electronic equipment. I made the following video detailing this problem before I fixed the scope. At the time, I didn’t know what was wrong with the scope but I had a pretty good idea. I’ll give you a hint — if you are thinking along the same lines as I was at the end of that video, you’re wrong :-)

In the coming weeks I’ll post the actual repair, but play along at home and see if you can figure it out.