Old power supply
This PSU was build by my father back in the 80’s. It has served him well and after he was promoted to glory in 1998 I have used it on my workbench. Today I opened up this old power supply. See photos below:
From a code on the PCB inside (see photo on the right), it appears to be a design that was published in a Dutch magazine called “Elektuur” in december 1982. That figures; my dad was always reading that…
The large over-spike that I was able to measure yesterday could have been caused by an old – worn out – main electrolytic capacitor, that’s the large round yellowish blob on the left on the last picture.
To be able to establish wether or not this capacitor is the problem, I have to take it out of the circuit, at least at one side. Otherwise the rest of the circuit would influence the measurement results.
I first tried the component tester in the analog oscilloscope:
This component tester indicates that the capacitor is a dead short. Further measurements with a multimeter an a resistor show that it is charging and de-charching in a seemingly proper rate
So I performed another measurement, now with my new scope. The vertical scale is set to 2 Volts per division and the horizontal time scale to 1 second per division.
In this measurement you can see that the time to fully uncharge from 5 Volt is a little over 6 seconds, with a resistance of 240 Ohms over the capacitor. We are talking about a 4700 uF, 63 V capacitor, so the test not entirely adequate, but I’m now reasonably satisfied that this large capacitor is still okay.