[Thursday] Engaging evening task

[fred tanner]

My DMM has a capacitance setting.  I use it regularly to measure capacitors
for fans, air conditioner compressors and motors.  It's a good tool.
f

On Thu, Jun 20, 2019, 10:20 PM Chris Prata via Thursday <thursday at newsm.org>
wrote:

> A little update, even though I was looking for an example dead short
> capacitor for the EE #2 night, I did not know that leakage could be seen
> with a VOM, nor really familiar with a VOM. So, I looked that up and
> determined one should be on my bench.
>
> As luck would have it, someone was selling a lot of three Simpson 260's
> online for $10. And he was willing to mail them. They arrived today and the
> one good one with a calibration tag was actually a high accuracy 270-5! After
> replacing the batteries, its readings match the DMM for volts and ohms very
> closely of the few values I checked.
>
> So thanks Dave for the reply below because it moved me (and my bench)
> forward.  🙂
>
> For the curious:
> https://simpsonelectric.com/products/test-equipment/vom-multimeters/270-5-270-5rt
>
> ------------------------------
>
> *From:* David Crowell <ka1edp at yahoo.com>
> *Sent:* Wednesday, June 5, 2019 8:44 PM
> *To:* Thursday NEWSM; Chris Prata
> *Subject:* Re: [Thursday] Engaging evening task
>
> Hi Chris,
>
> The best way to check an electrolytic capacitor is to use a VOM, not a
> DMM. The VOM will measure the leakage of the cap and the one with the
> lowest ohm reading is what you want.
>
> First you need to find out which VOM lead is negative. With the old VOM I
> use (NRI), the Red lead is actually the negative lead when measuring
> resistance. This is from the VOM's internal battery. I have heard this is
> not unusual. Use your DMM to check the polarity.
>
> Next, set the VOM on it's highest resistance setting. Connect the VOM to
> the cap - negative to negative. The VOM will jump up to a low resistance as
> the cap charges and then slowly increase to a few megohms if the cap is
> good. Finding an electrolytic with a dead short is pretty rare.
>
> Instead of putting a wire across a cap to simulate a short, you might want
> to use a low value resistor. If the radio is plugged into a plain power
> strip, you can use the power strips switch to turn the radio off quickly if
> needed. I wouldn't use a line suppression power strip.
>
> In the 60 years or so that I have been working on old radios, I've never
> used a light bulb as a line draw tester. For several years now, I have used
> a variac with an ammeter. If there is a vacuum tube rectifier, a solid
> state substitute needs to be used at low line voltages. I will be at the
> Museum this Saturday.
>
> 73,
> Dave, KA1EDP
>
>
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