0
\$\begingroup\$

I have a HP 8568A (+ HP 85662A display module) spectrum analyzer.

In the last 2 days, I had 3 caps that released the magic smoke.

On the following schematics there is a capacitor C1 that I marked. The original, 40 years old ones exploded in about a minute, which is no surprise. On the other hand, the new one I bought also exploded. Capacitance is the same, 100nF.

enter image description here

What could be the reason for that? What kind of capacitor should I use here?

Old one: enter image description here

New one: enter image description here

\$\endgroup\$
3
  • 1
    \$\begingroup\$ What is your mains voltage? What type of capacitor (make, model, link to datasheet?) is the new one? Are you sure it is a Class X safety capacitor, meant for direct and safe connection between live and neutral? \$\endgroup\$
    – Justme
    Sep 13, 2020 at 20:26
  • \$\begingroup\$ 240 VAC is the nominal voltage from the mains. In real circuits, things like surges and switching noise will get you transients above the nominal voltage. You are probably getting a transient that is low enough in frequency that the emi filter coil isn't taking out. \$\endgroup\$
    – scorpdaddy
    Sep 13, 2020 at 22:11
  • \$\begingroup\$ It also depends on the waveform; e.g. if used with a square-wave inverter (from a photovoltaic supply), that puts more strain on the caps and harmonics might hit the resonant frequency of the L-C combo. Also check that the AC mains is balanced to ground - if you have a floating neutral, one side might be getting far more than half the voltage. \$\endgroup\$ Sep 13, 2020 at 23:18

0

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Browse other questions tagged or ask your own question.