Longtime contributor Bob Meister from Hamden, Conn., writes in response to Tom Osenkowsky’s recent contribution with respect to equivalent series resistance (ESR) and the Sencore LC-75 Z-Meter being used to check capacitors.
Bob adds that capacitance value, leakage resistance and ESR are the primary measurements for electrolytic capacitors, which seem to go bad much more frequently than smaller capacitors such as disk, Mylar, film and mica.
Besides the Sencore LC-75 Z-Meter, there are alternatives you may already have handy to test these components. Many digital multimeters are able to measure the capacitance value, and all can measure resistance.
However, Bob has found that auto-ranging DMMs can often give a misleading leakage value because they keep changing range and indicated resistance. In many cases, a good old Simpson 260 VOM does a better job of measuring the leakage.
ESR, however, requires something a bit more sophisticated.
Bob uses the Peak Electronic Design ESR-70 (available for less than $150 on Amazon), which fits in your hand, operates on a single battery and can test just about every electrolytic capacitor you may run across.
Readings are fast and simple: turn the unit on, connect it to the capacitor and it automatically senses, discharges and begins analyzing the part, displaying the value in microFarads from 1 to 22,000 and the ESR in Ohms from 0.00 to 40.0. It can also measure ESR in-circuit, which is a great timesaver when troubleshooting. The ESR function can also be used to measure the resistance of things like transformer windings and coils. It shuts itself off 15 seconds later, conserving the battery.
Capacitance and ESR are not the only things that can indicate a failed capacitor.
Fig. 1: Note the “domed” tops of these “bad” capacitors.
Fig. 1 shows a capacitor bank in a QSC MX1500A amplifier. Each cap is 15,000 μF, 50 VDC. Note that there’s a black fiber cover over the top of each cap and most are slightly domed upward (convex). These all measured perfectly fine on every meter Bob had, but the domed top was the give-away. They all were replaced.
This amp also had a shorted bridge rectifier, several open fuses and burned 5 Watt resistors and several broken/burnt circuit traces, but it all was repaired and worked fine.
Fig. 2: Domed tops and leaking electrolytic.
Fig. 2 shows another QSC MX1500A amplifier, but all of the capacitors have pushed their tops upward, as in Fig. 1. Additionally, they have leaked electrolyte out the vent slits at the top. The “goo” at the top stuck to everything — the workbench, papers, Bob’s hands, you name it. These, too, had black fiber covers on them, but the caps got hot and the vinyl wrappers shrunk and pulled down the sides, releasing the black covers which got sucked up by a vacuum cleaner before Bob got the amp. A few loose covers remained lodged under the main board.
Each of these caps measured between 14,000 μF and 14,500 μF and the ESR was 0.01 ohms, about as good as you can get for a 15-year-old 15,000 μF capacitor, and better than the brand new ones.
Fig. 3: The capacitor bank after replacement, with a “bad” capacitor on the right.
Fig. 3 shows the above amp after the capacitors had been replaced with identical parts. The extra cap on the right is one of the ones that had leaked and pushed its top upward. Notice that the tops of the eight new ones are slightly concave (indented/depressed), and they don’t have black fiber covers on them anymore.
For comparison, the brand-new caps measured between 13,500 μF and 14,000 μF, and the ESR was 0.01 ohms. At 20-percent tolerance, all the caps were within spec.
A bulging leaking cap is a good indication that it must be replaced, even when all the test equipment in the world says, “Electronically it’s fine because it still has its rated value of capacitance and ESR.”
Sometimes the best test equipment is the human eye and nose.
Think your computer has a virus?
Newman-Kees RF Measurements principal Frank Hertel suggests that engineers carry a couple of useful Norton utilities found at https://security.symantec.com/nbrt/overview.aspx.
These will help you to recover or restore infected browsers and computers, he says. Frank saved days of work using these utilities, when a “paid for” virus protection software failed to protect a computer.
There seems to be an upsurge of sites that download malicious Trojans and similar viruses where the protection programs are missing.
Innocently clicking on a screen element, that has been purposelymislabeled within a site page, can initiate the problem and render all your browsers virtually useless.
Resident programs may work properly, but your internet browser(s) become useless from overwhelming pop-up ads which cripple their function.
In Frank’s situation, it appears that what gets unwittingly downloaded is not caught by the virus protection software, as it is structured like a valid executable program, since it is unintentionally downloaded when one clicks on a purposely mislabeled page element.
At the Symantec site, you will be able to download two separate small and effective repair elements from Norton. Most of the time, you’ll only need to use the Norton Power Eraser; however, severe cases will require the use of the Norton Bootable Recovery Tool.
Frank admits there are other programs that one can use, but this one fixed his problem quickly — and it was free.
Author John Bisset has spent 48 years in the broadcasting industry and is still learning. He handles West Coast sales for the Telos Alliance. John is SBE-certified and is a past recipient of the SBE’s Educator of the Year Award.