Just why do you replace all those capacitors?

Capacitor

In my role as a business owner in the repair and refurbishment industry I get asked many technical and non-technical questions on a daily basis. Just last week I was asked by a guy in a maintenance role

“Just why do you replace all those capacitors?”

We were discussing a repair that we had recently carried out for him on a sizeable VSD, and I was showing him photos of the power PCBs and driver PCBs. He admitted to me that he could identify the capacitors but he didn’t know why we replaced them. Now here’s where I have a great deal of admiration for him, he didn’t know, so he did the right thing, he asked!

Now the first thing I said to him was that you don’t have to replace electrolytic capacitors, it just helps to keep electronic equipment running for longer if you do. Basically, by replacing electrolytic capacitors you will improve operational life of the VSD.

Electrolytic capacitors, or to give them their correct term, aluminium electrolytic capacitors are used in electronic circuits to carry out many functions – hold a charge, pass AC current, block DC current flow, smoothing, timing, filters etc. If you have any piece of electronic equipment there will be numerous electrolytic capacitors on the PCB. A failure of just one of these capacitors can and will cause your entire unit to fail.

By the time we see an electronic item for repair, be it a PSU, a variable speed drive, a servo drive, a HMI etc. it will have been in service for several years. The capacitors will have been doing their job, they will be getting a little tired.

Electrolytic capacitors due to their construction (two conductors, usually a sheet of aluminium foil separated by a liquid electrolyte and rolled up; a bit like a Swiss roll!) have a finite life. They weaken, become dry, become resistive, increase ripple, all things you don’t want in an electronic circuit. Most capacitors in electronic systems these days are rated to a maximum operating temperature of 85 degrees Celsius. We like to improve the reliability of equipment we repair and refurbish, so as an internal repair standard we replace all electrolytic capacitors with 105 degree Celsius types. It’s just one way in which my company and other quality progressive repair companies can help to keep electronic equipment running longer and to provide quality reliable repairs, we upgrade the quality and durability of wearing parts before they fail.

The conversation progressed as I started to explain the other components we replace as standard to enhance reliability further.

  • We replace all opto-isolators as they too have a finite life with the IR transmitter or receiver weakening.
  • All relays are replaced as the contacts can become restive.
  • We replace all cooling fans as the motor bearings will fail.
  • We reflow all solder joints as they can become dry and resistive.
  • Any component we see that is visibly heat damaged will be replaced.
  • All insulators will be replaced as they can become brittle.
  • Heatsink compound is renewed as the thermal properties change over age.

So what started as a conversation regarding capacitor replacement really evolved into a full discussion regarding what we do to ensure our repairs are reliable and long-lasting. It was my customer who eventually said that we don’t just repair electronic equipment, he said that we really do refurbish everything and make it the best it can be.

Correct, yes.

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