One of my free spaces within the Elektor editorial team goes by the motto: one man’s grot is another man’s gem meaning I am out and about collecting discarded electronic equipment, which gets restored and/or written about for the general amusement of my readership. Recently on one of my friendly pillaging tours in the Eindhoven area I got two Tektronix 2235 oscilloscopes thrown in – literally – when I was just about to shut my car booth, having loaded half an e-workplace ground to a halt I guess around 1990 and then quietly left to collect dust. Fortunately these Tek 2235 scopes are made for field use hence lightweight. BTW they’re 100 MHz dual trace.

One of the 2235s appeared to have a problem with an overheating power supply, which I decided to remedy. How difficult can that be if you normally handle beat up Teks with a dozen supply voltages and 50+ tubes inside? This 2235 was marked by the familiar “dust & arc” smell coming from the PSU area. So, let’s open up the thing and dust off the usual suspects: HV transformer, diodes and caps. All went well using my $5 Jackly 32-in-1 bit set (see photo) until I got to a Torx-7 screw on the back of the instrument  which was secure enough in the main frame to destroy the Chinese T7 bit as if it were chewing gum. I then found it surprisingly hard to buy a spare Torx-7 bit locally, for use with my ¼ inch T-grip tool. In one hardware store I was told there’s only T6,T8, T10, and no T7 :-). Then my colleague Thijs Beckers suggested using the new iFixit toolset Elektor is retailing.

iFixit toolsets are popular among repairers of smartphones and all sorts of games and computer stuff, so I thought why not for a 1980’s oscilloscope? (made in the UK)
Low cost, awful performance $5 toolkit.

Using the TR-7 bit (= Torx Security) in the iFixit toolkit the stubborn Torx-7 screw was out in a jiffy, as was the high voltage protection cover followed by the entire PSU board. Although the TR-7 bit was an accurate fit in the screw head and took no damage from the force I had to exert I still feel it could benefit from hardening. I found the reverse-operating precision tweezers in the toolkit extremely useful to capture and NOT lose some of the small PCB screws. Likewise the plastic ‘opening tools’ (which look like mini tyre lifters) for prising the pretty large board off its spacers with no risk of damage to the sides.

Amusingly there are iFixit “motto’s” printed on some of the tools, like “repair is noble” and “this tool is designed to break before your device does”. I dusted off the PSU board, gave it a good clean with IPA, replaced one bulging electrolytic cap (with ESR okay though), and reassembled the ‘scope using 3 Torx bit sizes: 7, 8 and 10. With the scope working but not in its case yet I used one of the ‘spudgers’ in the kit to gently rap the PCB and some components in search of ‘microphony’ in the upper trace I noticed once only when connecting my probe to the BNC socket on the front panel. All was fine however and the effect has not showed up since.