"Why do you replace all those capacitors?"

In my role as a business owner in the remanufacturing and repair industry, I often get asked many technical and non-technical questions. Just the other week I was asked buy a procurement officer at a customer's site this question -

"Why do you replace all those capacitors?"

We were discussing a repair that we had recently carried out for him on a 280Kw variable speed drive (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. He thought that by doing so, it would just add to the cost of the repair. 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, a repair can be carried out without doing so. However we prefer to protect his production up-time. We prefer to service and remanufacture what we see for repair, it just helps to keep equipment running for longer if you do. Basically, by replacing electrolytic capacitors you will improve operational life of the VSD; and i would argue it brings the VSD into an as-new condition.

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 or degradation in performance of just one of these capacitors can and will cause your entire unit to fail, and then the production line is supports will stop.

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 and update them with quality, 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.
• (We do more but that's enough of a list for now).

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.