New owner of a Greenie

[JPG]

Initial testing indicates the capacitor is shot. I connected my multimeter and got nothing. The windings appear to be okay, reading 8 ohms

How did you check the capacitor? If you check a capacitor with a multimeter set to Ohms you will get infinity, an open circuit (nothing?).

Maybe!

[Sconnie]

How did you check the capacitor? If you check a capacitor with a multimeter set to Ohms you will get infinity, an open circuit (nothing?).

I discharged the capacitor and attached the leads from the multimeter. If it’s good it should start at 0 and climb to infinity as the multimeter charges it. This one started at 0 and climbed all the way to 0.09. If I’m wrong and that’s not the problem it’s not a huge amount of money gone.

In the meantime I’ve been taking the headstock apart and cleaning 70 years of sawdust and grime out of it.

[JPG]

Multimeters vary and react differently. That said displaying low resistance that increases as the cap charges is indicative of a capacitor acting like a capacitor.

[DLB]

Multimeters vary and react differently. That said displaying low resistance that increases as the cap charges is indicative of a capacitor acting like a capacitor.

I used to check them that way, pretty effective with an analog meter. You can also switch polarity by swapping leads and see discharge behavior. But the last failed one I had a couple of months ago, on a pump, measured 18uF should be 30uF. Still a capacitor acting like a capacitor. Very glad I checked it with a multimeter that has a capacitance function! Saved me a lot more work, and probably a lot more expense than if I had done it the old way.

- David

[edma194]

A little piezo speaker can make a neat little capacitor detector. Just attach the speaker between the cap and ground through a resistor and you'll hear the distinctive 'winding down' sound of a capacitor discharge through the speaker. Long ago a friend of mine built his own logic probe with that feature. Very handy to just listen instead of interpreting readings through a meter.

[JPG]

A little piezo speaker can make a neat little capacitor detector. Just attach the speaker between the cap and ground through a resistor and you'll hear the distinctive 'winding down' sound of a capacitor discharge through the speaker. Long ago a friend of mine built his own logic probe with that feature. Very handy to just listen instead of interpreting readings through a meter.

'???

[edma194]

Just try it. It's like the sound of air escaping from a balloon as the cap discharges.

[JPG]

Sure the piezo is not creating the 'hiss'?

[edma194]

Sure the piezo is not creating the 'hiss'?

Well of course it is, that's the point, you get to hear the cap discharging through the sound on the speaker.

[JPG]

Question is what is causing capacitor discharge to create a current that will produce sound from the speaker? A decaying current should not create an audible frequency(or any frequency) to be induced in the speaker.

Now explain to me what a piezo speaker is?