Maintenance & Repair for Electromechanical Switches

Electromechanical Switch Technology Includes:
Electromechanical switches: basics     Specifications & parameters     Switch maintenance & repair    

Electromechanical switches can operate reliably for many operations, but over time and use, their performance can degrade or the switch can fail, causing the whole equipment to stop working.

Fortunately there are several methods by which the switch performance can be restored and the whole equipment brought back to life very easily and cost effectively.

There are a few easy techniques that can be used to bring old switches back to life, often without removing them from the equipment.

Causes of failure in an electromechanical switch

There are many ways in which electromechanical switches can fail, or their performance can degrade. Time and usage can result on the switching action becoming less effective and often it is relatively easy to effect a repair, but it is often necessary to understand the way in which the switch can degrade.

• Contact arcing:   When the contacts are made and broken, there is the possibility of some arcing and this can degrade the contact. Over time the contacts can become pitted and dirty and this will degrade the performance considerably.

• Contact dirt:   Over time the contacts of switches, especially those that are open to some degree can pick up dirt and grease, especially if they are in a dirty or greasy environment. Domestic kitchens can be one area where grease and grim can enter the equipment and cause a build up of dirt on the switch contacts. If a smoker is present, this also causes a significant build up of dirt over time. It is surprising what damage being in a cigarette smokers environment can cause. Over the years there can be a significant build up of tar on many surfaces including those of the switch.

  The build up of dirt will eventually cause the contact resistance to increase, sometimes to a degree that can cause the switch to fail.

• Lack of use:   The use of the switch and the movement of the contacts has a cleaning action on the contacts. If the switch is not used and left in the same position dirt and corrosion can build up cause the contact resistance to increase.

Ways to fix faulty switches

There are a number of ways in which electromechanical switches can be fixed and returned to good reliable operation. Many of the methods are very simple and easy to implement and can prevent the replacement of the whole switch, giving it many more years of useful life.

• Activate the switch:   If the switch has been left in the same position for a long time, then dirt and corrosion can build up on the contacts and these can prevent the conduction of current. This can be especially true of the switch only carries a low level of current.

  Simply actuating the switch - moving it from one position to another a few times can sometimes clean the contact and enable successful operation.

• Use of switch cleaner:   It is possible to buy purpose manufactured switch cleaner, normally int he form of a spary, although dispensers with a long nozzle are also sometimes available. This is essentially a solvent for grease and it is often combined with a conductive form of lubricant. This dissolves the grease and and provides lubrication for the contacts. It is ideally intended for rotary or sliding switches.

  For the switch cleaner to work, the cleaner should be applied to the contacts of the switch, it should be left for a short while to enable the grease and dirt to the softened, and then the switch should be moved. This will ensure that the contact areas of the switch are free from grease and dirt and that the contacts can make good contact with each other.

  Although most switch cleaners and switches will be fine, it is possible that the solvents in the cleaner could dissolve some forms of plastic used in switches - this is not normally the case, but something to be mindful of.

  Many years ago, I cleaned a switch and a month or two later the contacts came away from the centre rotary section of the switch as a result of the switch cleaner - it has softened the plastic holding the centre rotary contact. The repair required the multiway switch to be disassembled - not an easy job - repaired and then re-assembled. It has always been a warning to me.

• Run current through the switch:   In some cases it is possible that even running the current required for operation of a circuit can help burn through the dirt and grime on a switch.

  In everyday usage, current often passes through the switch and will help to ensure that it does not oxidise and cease working. Therefore using the switch and passing current through it often helps. Issues can be experienced if the switch takes very little current as in the case of band-switching on radio receivers. Often the front end tuning switches may carry virtually no current.

• Manually clean contacts (with care):   In some instances switch cleaner may not be available, or significant oxidation may have occurred on the contacts. This can be cleaned off using a slightly more aggressive approach, but even so care is needed.

  Ordinary paper has sufficient abrasion to clean the oxide from the contacts. The paper can be run over or through the contacts dependent upon the mechanical construction of the switch. If this approach is taken great care must be taken at all times not to damage the construction of the switch in any way and in particular the contacts which can sometimes be quite delicate. Running the paper a few times over the contacts, or sometimes through them depending upon the construction can remove dirt and oxidation - it is often possible to see this deposited on the paper.

  One word of warning: under no circumstances should any abrasive papers be used however fine. They will remove the any surface coating and lay up problems for the future.

It is obviously not possible to repair all types of electromechanical switch, but a good attempt can be made at many types.

Switches that are enclosed are normally much more difficult to repair - toggle switches are a typical format that are not always easy to fix. Often the best that can be done is to actuate them several times to try to clean the contact surfaces. If they need to be taken apart it will be found that they are normally held together with rivets, and sometimes these can be removed to effect a repair if absolutely necessary. Beware they they tend to spring apart as the toggle action is normally spring loaded.

Switches that are open tend to be easier to fix - slider and rotary switches often have a little more access, either for switch cleaner or for even gaining access to the contacts themselves.

When undertaking any repair, it is obvious that the equipment should be disconnected from any power to prevent accidental electric shocks, or damage tot he equipment.

Fixing a switch using the methods above can provide a simple and effective way of repairing an item of electronic equipment. Items like domestic radios and so forth can often be left unused or the switches not moved for years on end and this in itself can cause the radio or other item to fail. When looking to repair some items, looking at obvious remedies first like fixing the switch can pat significant dividends. Often the switch is easy to repair and enables considerable costs to be saved.

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