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Hameg HM207 scope

This is a very usable transistorised scope for hobbyists and small workshops. It has a 10 MHz vertical bandwidth and a time base with synchronisation that works surprisingly well. Hameg sold it either as a kit or as a factory-made unit. The kit featured in a review in Radio Bulletin in March 1974.
HM207 chassis

Chassis with front taken off.

This scope belongs to a friend of mine. He said it had stopped working and I volunteered to fix it. I greeted the opportunity to open up and examine one of these small hobby scopes I had been reading about when I was young.
HM207 chassis side view

Side view of chassis.

I opened the case and started to examine it. The soldering work looked excellent so I think this scope is either a factory-built specimen or it has been assembled by a very experienced hobbyist. As I had no circuit diagram, I drew the circuit digram of the vertical amplifier myself. Interesting, much like the last DIY scopes described in the magazines in the seventies.
HM207 input

BNC input with AC-GND-DC switch.

Analysing the circuits of the Y amplifier by following the wiring, I found an input stage consisting of two BF245 FETs. At first I thought the input stage was blown. But after some examination, I found the input switch (positions AC/Gnd/DC) to be interrupted. Replacing it cured the scope and now it is working fine again.

	   HM207 in RB magazine.

HM207 in RB magazine.

In March 1974, an article was published in the Radio Bulletin magazine about this nice little scope. It contained a reviwe, gave a discussion of the assembly of the kit and listed the specifications. RB did not publish the circuit diagram, though. Fortunately, I was able to fix this HM207 without the schematics.

Copyright © 2002 by Onno's E-page         published 2002-11-11 , last updated 2008-08-19