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enter image description hereI have an old player piano from the late 70s that had a large capacitor go bad.

I replaced it with the necessary 200 V 1900 uF capacitor. If I understand correctly the capacitor needs to be charged in order to function properly. Is there a safe way to charge the capacitor while it's attached to the board, or should it be charged separately then installed? What would be the safest way to charge this capacitor?

Thanks for the help! This piano is an antique and I don't want to see it junked.

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  • \$\begingroup\$ What use do you see in charging it other than in normal operation? \$\endgroup\$
    – greybeard
    Jul 15, 2023 at 16:44
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    \$\begingroup\$ You might be thinking about the precaution to apply voltage slowly, in several steps, to "form" the dielectric of large high voltage capacitors (such as in VFDs) when they have been in storage for a long time. knowledge.electrochem.org/encycl/c04-appguide.pdf \$\endgroup\$
    – PStechPaul
    Jul 15, 2023 at 21:15

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The capacitor will become charged in the normal operation of the circuit.

It is important that it is installed in the correct orientation—it has a positive side and a negative side which must match the way the old one was installed.

You do not want to charge it before it is installed. Definitely do not touch where it is soldered to the board once it has been powered on because you will get a nasty electric shock.

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  • \$\begingroup\$ A 200V 1900µF 1970 player piano capacitor probably is a motor auxiliary phase capacitor for use with 120V mains voltage. Those are AC capacitors: there is no wrong orientation. Of course, a photograph or schematics would help. \$\endgroup\$
    – user107063
    Jul 15, 2023 at 19:56
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Just install the capacitor. Don't try to charge it. The piano circuitry will do the charging.

If the capacitor is electrolytic (polarized), pay attention to the positive and negative during installation.

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  • \$\begingroup\$ Motor capacitors are electrolytic and bipolar, so that's a false equivalence. \$\endgroup\$
    – user107063
    Jul 15, 2023 at 19:57
  • \$\begingroup\$ It is an electrolytic can capacitor. I wasn't sure if it needed charged because after I installed it and powered it on the piano came to life for 1 second, then faded off immediately. I have the positive terminal (screw type capacitor) where the board has it indicated. I appreciate the quick response! \$\endgroup\$
    – jay cee
    Jul 15, 2023 at 20:38
  • \$\begingroup\$ In that case, there seems to be something else wrong. The large blue capacitor is almost certainly a polarized electrolytic, while the other two gray cans are probably non-polarized AC capacitors. They are also likely bad, or deteriorated with age, and should be replaced with the same type. Please show the labeling. You will need to be careful doing more troubleshooting. Hopefully there is just a blown fuse, But before powering up again, use a Variac to bring up voltage slowly, while taking measurements. Try to sketch a schematic and perform a proper test procedure. \$\endgroup\$
    – PStechPaul
    Jul 15, 2023 at 20:58

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