Remember that old Nixie Clock? For a while it ran properly, but now it skips time again at random intervals. So I got that big capacitor out that I suspected right away, because it has been in there for over 40 years. And unlike me, these things do not age well…
It’s that big yellow one next to the transistor on the top PCB. 16 Volts, 2200 uF.
I got it out and compared its ESR (Equivalent Serial Resistance) to that of e new one (albeit that the new one is 1000 uF). I measured using a square wave of 200 kHz.
The ESR at this frequency should be practically zero. The new capacitor indeed has a very small ESR of 0,08 Ω, while the old one has 1,9 Ω. The difference seems to indicate that the old one is worn out. So I ordered new capacitors and will substitute it.
To be continued…