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Tektronix 1240 Logic Analyzer
Posted: Wed Oct 11, 2023 7:30 pm
by dl6lr
I got a Tek 1240 from a friend. Offered for free. "Distorted image" was the symptom. So I said yes. It took some time for the instrument to arrive.
I repaired it. The offending part was a kind of Zener-Crapacitor, an electrolyte being installed in wrong polarity in the factory.
My repair report, unfortunately in german (I promised my friend to report to him).
http://www.laengerich.com/tmp/Tek1240/T ... Repair.pdf abt. 10MB
Haven't tried to Google-xlate it...
Re: Tektronix 1240 Logic Analyzer
Posted: Fri Oct 13, 2023 12:24 pm
by Zenith
An electrolytic capacitor installed with reverse polarity in the factory, is a very unusual fault. I wouldn't expect it to last long at all. I'd have thought it wouldn't survive factory testing, and certainly not the guarantee. I'd guess it was operating at a low voltage and was used in a feedback loop or such.
I can see it happening in the course of repair. Sometimes the silk screening showing the polarity is confusing or just wrong. Usually it's easy to tell if a capacitor has been factory fitted or is a replacement.
Re: Tektronix 1240 Logic Analyzer
Posted: Fri Oct 13, 2023 11:34 pm
by vk6zgo
Zenith wrote: ↑Fri Oct 13, 2023 12:24 pm
An electrolytic capacitor installed with reverse polarity in the factory, is a very unusual fault. I wouldn't expect it to last long at all. I'd have thought it wouldn't survive factory testing, and certainly not the guarantee. I'd guess it was operating at a low voltage and was used in a feedback loop or such.
I can see it happening in the course of repair. Sometimes the silk screening showing the polarity is confusing or just wrong. Usually it's easy to tell if a capacitor has been factory fitted or is a replacement.
It happens in the best of families.
I remember, whilst doing "scattergun" replacement of electros in a (then) 15 year old Sony BVM1410 Broadcast standard picture monitor, coming across a bunch of them which had been factory installed in strict adherence to the silkscreen polarity marking.
Tracing through the circuit showed that they were all reversed, but they had survived all that time----go figure!