Semi-pseudonymous software engineer Dylan "SunEstra" has written up the process of turning a piece of junk from a literal dumpster dive into a functional piece of test equipment: restoring a Tektronix 2465B 400MHz oscilloscope.
"I was not expecting to find a scope in that dumpster as I usually only find some computer peripherals and components when I’m lucky enough," SunEstra writes of the dumpster at which she is a regular visitor. "However, this old analog scope was there, in pretty good shape, with its blue probe pocket on the top, the original Tektronix handle, and its front cover. Once I [had] removed the front cover, I discover the unit’s front panel — unveiling a Tektronix 2465B 400MHz unit. A CRT analog oscilloscope from the '90s."
Launched in 1989 and discontinued in 1996, the Tektronix 2465B was one of the later entries in the long-running 2000-series — the first models having launched in 1982. Offering 400MHz of bandwidth and four channels, the analog scope was a go-to choice for a range of engineering and debugging tasks — but was supplanted in the company's line-up by later digital storage oscilloscopes. Old it may be, though, but "free" is a hard bargain to beat — though SunEstra soon discovered the reason the device was in the dumpster.
"On the first start-up, the scope started blinking on many LEDs of the front panel, making relay clicking noises, then got stuck with a green LED light on the ADD mode with nothing displayed on CRT," SunEstra explains. "Wah wah wah wahhhhh… The error code 40, which sometimes turns to 44 on different boots, corresponds to 'positive level too positive,' whatever it means."
Investigating internally, SunEstra found a number of suspect faulty parts in the circuitry — including capacitors which had bulged and leaked their electrolytic. A quick soldering station upgrade later, to add a hot air gun, and the repair could begin. "After identifying the leaky caps and considering dead neighbors, I used Page 305 [of the manual] which is the bill of materials of the original board," SunEstra explains.
Just replacing the parts didn't prove enough, however, with the discovery of a micro-rupture in the circuit board itself. "I scratched the trace to reconnect the pad with the trace," SunEstra explains. "I did the same for the missing pads: I scratched the related trace, tin them, and then introduce the component to solder them. The result is quite as bad as the initial situation: it will work, but it is not elegant. Not a problem." Finally, the scope booted — and even had enough charge left in its battery-backed SRAM to retain configuration settings.
The full project write-up is available on SunEstra's website.