- April 9, 2018 at 6:18 pm #11636radio8zSenior Moderator
Total posts : 247
Recently I have been experiencing degraded performance of some of my electronic devices. As an example, a video capture device began dropping frames, stalling video, and then stopped working over a time of a few days. This device is powered by one of those small, light weight wall warts which is rated 5V at 2A. Having seen several “slow deaths” of digital and analog devices before which were caused by power supply problems the first thing I did was unplug the DC connector and measure the voltage output of the wall wart which was 3 volts instead of 5.
I was able to crack open the wall wart case and saw two capacitors which were swollen with the tops bulging. Removing the caps and testing them revealed greatly reduced capacitance and increased ESR. Using capacitors from my parts bin as replacements brought the supply back to 5 Volts and the video device now works. Lesson is that when a device fails slowly it is likely a power supply problem and if the supply is a wall wart then replacing this probably will solve the problem and there will be no need to junk the whole unit.
I had the same problem with both of my Alesis Nanocompressors, which are analog, but this time the bad caps were in the devices and not in the wall warts. Once again swollen caps were seen and replaced and the units are working again. The symptom was increased hum in my broadcast signals.
Same story with my desktop PC. Replacement of two swollen caps in the power supply fixed the problem of frequent system errors.
So what’s the deal with capacitors these days? My take is that manufacturers are driven by price and equipment size. Making things small and cheap means using miniaturized capacitors obtained at a low price. Miniaturizing caps means designing them to operate at the limits of voltage with minimal safety margin. Additionally, making devices as small as possible means crowding of parts which increases the operating temperature. This increases the strain on the part which shortens its life.
If you are of a mind to try to repair your equipment then do a visual inspection of the circuitry looking especially for capacitors which have leaked or bulged. Rubicon and Nichicon 105C rated caps have a good reputation for reliability. Keep in mind that replacing only the obviously defective capacitors means there are others with many hours on them and they may soon fail. This has not been my experience but it is possible.
At least check the voltage output of wall warts and replace these if needed as repair is not a good idea since the case needs to be cracked open and shouldn’t be done unless you know about safety and proper replacement components.
In days bygone vacuum tubes were the primary suspect for failures, now it is capacitors.
Hope this can save you some time and money.
April 9, 2018 at 6:52 pm #57104BowlingSuperiorGuest
Total posts : 45366
Yes I have seen the same thing you describe with Wall-wart capacitors and current leakage. One way that I have been testing these is with a variac with a built-in current meter, with no load slowly increasing the voltage to see if there is a point where the current spikes up – there should not be any spikes in the current.
I use a Sencore Powerite unit which has both a voltmeter and ammeter, I use this all of the time to check electronics for sudden current spikes.April 9, 2018 at 8:25 pm #57105Carl BlareGuest
Total posts : 45366
As has happened before, Neil’s posting about wallwarts and electrolytic capacitors opens my mind to possibilities I hadn’t previoously considered.
Two Hi8 cameras have been stowed for several years in a carrying case since they both failed, leaving me believing it was the cameras themselves at fault, which is still possible. But I hadn’t considered the power supplies as being perhaps defective.
One of them is an early Sony Hi8, which on one occasion was sent away for repair to a former Sony engineer who retired in Rogers, Missouri and opened a home repair depot. He quickly made the camera work like new and we had a pleasant phone conversation in which he explained two weaknesses in that model, number one being caps which failed after very short life. The other problem was the alignment mechanics which he said were not sufficiently locked down at the factory and tended to drift, the result being that Hi8 tapes made on different camcorders could not be aligned, causing a streaky poor playback. A few years went by and the camera failed entirely, but the Sony engineer had died of cancer and the digital age was starting, so the camera is put away.
Another amazing camcorder made by Minolta had the unique distinction of being a 2-chip camera, giving it sharper and more accurate color than 1-chip cameras (the “chip”) being the image grabbing device that picks up the picture. A nearby Minolta service desk existed at an electronic services company, and Earl, the tech, told me the same tale about capacitors going bad and repaired that camera, which later failed for what seemed like the last time. Earl and his company are gone.
But now I have new hope and will check the power supplies to find out if that’s the only problem.
Part15(dot)us is the boss!April 10, 2018 at 3:34 am #57108MarkGuest
Total posts : 45366
The working DC voltage is chosen very near or slightly above the operating voltage and if the operating voltage is say 12 volts the caps ahould be rated at 25 volts and higher, the higher the better.
That’s the big problem and there’s usually ample room to replace with a much higher DC voltage than original as the size is not that much more.
They want to make the wall warts as compact as possible and don’t want to have space for caps a little larger.
Fortunately my transmitter and the FMR Audio compressor work on A/C not D/C so it’s just a transformer in the wall wart and as long as you don’t have a tug of war with cable or loose it they last forever. I have extras for back up.
The compressor has been working 24/7 for quite some time now and is perfect so the caps are pretty good I guess.April 10, 2018 at 4:01 am #57109jimhenry2000Guest
Total posts : 45366
Neil, that is great info and good to know! Replacing caps is simple and easy too.
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