Troubleshooting Bad Switches

 

If a switch on the control panel clicks normally and seems like it should work but the operation associated with the switch does not function, the board may have a bad switch. However, it is more likely that the switch is good but the soldering that connects the switch or its associated components has gone bad..

Bad Solder Joint

The switches on the control panel are all scanned using a procedure called "matrix keyboard scanning". In this manner, many more switches may be serviced than there are input lines on a microprocessor. If you find that only one switch is defective, then chances are, the connection to that particular switch has been lost.

Every switch connects to the others through a diode. These have designations such as D52 on the back of the board. Because of their small size, they have been difficult to inspect. During the vibration of shipment, it is possible for the solder joint to fail.

Examine the close-up picture below for an example of a good solder joint:

Note how the solder merges smoothly with the metal parts of the diode. Actually, the left solder joint has too much solder, whereas the right joint looks pretty good.

Often a bad solder joint will only be visible from certain angles. So if a switch is misbehaving, examine the diode very closely with a high power magnifier or a dissecting microscope.

The diodes are somewhat fragile and it is possible for them to crack. This is unlikely unless the board has been bent, but it is worth looking for when diagnosing problems.

Also note the solder on the switch itself. It has flowed neatly up the pin and on the board pad. All connections must be perfect for the switch to function reliably.

Links:

Cable Details    Upgrading the Internal Software    Release Notes

Inside the main control unit    Configuring a Motor Controller

Troubleshooting Bad Switches     More Pictures

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