The Capacitor Wizard by Martin Pickering
Written by Martin Pickering of 'Television Magazine' in the UK
Check out his web site at http://www.you-book.co.uk
This is no ordinary meter: It has been designed to check the ESR of electrolytic capacitors in circuit – a basic test of the goodness of these notorious components. It can also do other things, as Martin Pickering of the UK explains.
The Capacitor Wizard
A week or two ago one of my trade customers phoned me for help with a BT SVS250 satellite receiver. " I replaced all the parts included in RELKIT 17" he said, "but it still doesn't give any on-screen decoder messages."
I suggested that he used his wife's hairdryer on the main PCB, since the electrolytic capacitors in the video section are notorious as a cause of this symptoms, also streaky pictures.
An hour later he phoned back. "Your hairdryer idea didn't get me anywhere" he said, "waste of time. But I found the fault right away when I used my Capacitor Wizard."
"It was C232, and I found it with my Wizard."
"Ummm, sorry. What's this Wizard thing?"
"It's advertised in Television. Bought one. Wonderful. You should buy one."
Now I confess that although I write the occasional piece for the mag I don't often read the adverts. So this recommendation came as something of a surprise. Then there's the fact that your reviewer doesn't usually buy things. I mean, I wouldn't be right somehow to actually pay for something to review, would it?!
Anyway I sent an e-mail to SEME and ordered one. It arrived next day, and I posted my cheque by return.
My first impressions were that the meter was "chunky' and maybe on the expensive side. It's housed in what is obviously a proprietary molded black box, with brown feet glued to the underside. The meter movement seemed to have been fitted as an afterthought: it stands a centimeter proud if the box. The unit is large in comparison with a modern multi-meter. This was not going to fit in my pocket.
But first impressions can be misleading. This is an instrument that has been designed for a specific purpose, and part of that purpose is to sit in a workbench without wandering about with every draught from the window. The chunky box makes sure of that, and the brown feet are functionally perfect!
The face of the meter is colorful and easy to read. The unit's controls are simple: an on/off switch and two recessed preset adjusters that, so far, I've not had need to touch. The bright, yellow-painted cover might be chunky, but it's the sort of Morris 1000 type chunkiness you learn to love. And the probes – I just love to hold those probes!
Not a Capacitance Meter
"But," I hear you say, "I already have a capacitance meter."
Well this isn't a capacitance meter. What it measures is the effective series resistance (ESR) of electrolytic capacitors, and it does so with the capacitor in circuit
You will, of course, remember Ray Porter's excellent articles on the subject of ESR back in the January and April 1993 issues of Television. To recap, with an electrolytic capacitor's the ESR is a much better guide to the capacitor's state of health than its actual value. In a chopper power supply, to take one application, the electrolytics take a continual hammering from fast rise-time, high-current pulses. These can degrade a capacitor in such a way that is no longer able to smooth the pulses. Its capacitance value might still be all right, but its effective series resistance may be far too high. This is what the Capacitor Wizard measure.
How, I wonder, could I have managed without this instrument for so long? For years I've treated electrolytic capacitors with suspicion. I have replaced without testing them any were discolored or oozing, and have continually been surprised when the culprit turned out to be other than the one(s)I suspected. Then been even more surprised to find out that its capacitance value was almost correct.
Now, with the Wizard, I simply ensure that the big electrolytics are discharged, then prod each one with those wonderfully long-pointed probes. If the Wizard bleeps, the capacitor is OK: no need even to look at the meter. If it does not bleep, I look at the meter and make a judgment. If the meter's needle comes to rest in the 'compare' region, I do the test again with a new capacitor of the same value in order to provide a comparison. If the needle comes to rest in the 'bad' region, the capacitor goes in the bin and a replacement is fitted.
This works fine with electrolytics of value down to 10 microfarad. With practice, you can make a considered judgment down to 1 microfarad. Above 100 microfarad, the meter always bleeps unless the capacitor is bad.
How it Works
The Capacitor Wizard generates a 100kHz sine wave test signal of only 5mV RMS. This is insufficient to switch on any semiconductor device present, so the meter is not affected by other components in the circuit. As it measures reactance, it will happily ignore even a 100ohm resistor across the capacitor being tested. In fact the only times when it's fooled are when the capacitor under test is short-circuit – check with an ordinary meter if in doubt – or there's a good capacitor in parallel with a bad one. You soon get to spot these.
The Capacitor Wizard was designed by an American engineer who actually uses it himself. It shows! The instruction booklet is clear and concise, and even includes tables to enable you to check capacitors with values as low as 0.1 microfarad and small value inductors as well. There's also an explanation of how to check for leaky or short-circuit semiconductor devices. This meter is more versatile than you might think!
The total price of the Capacitor Wizard is $179.95 U.S. plus shipping and can be obtained from many distributors around the world or you can order directly from our online catalog. In the U.S. and Canada call 1-800-394-1984 or International call 316-321-2800 or fax 316-321-2803.
An absolute must for every Technicians Bench and Field Kit
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Order two...One for your bench and One for the field. This is an absolute indispensable piece of test equipment for the technician.