Shopsmith Forums

jsburger wrote: Mon Sep 05, 2022 9:48 pm

Sconnie wrote: Mon Sep 05, 2022 1:25 pm 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!

jsburger wrote: Mon Sep 05, 2022 9:48 pm 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.

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.

JPG wrote: Tue Sep 06, 2022 9:46 pm 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

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 wrote: Wed Sep 07, 2022 11:07 am 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.

'???

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

Sure the piezo is not creating the 'hiss'?

JPG wrote: Thu Sep 08, 2022 12:12 pm 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.

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?