The power switch on the DGCIII Digital Ion Guage controller (sometimes referred to as the DIG III) which is used on many older Physical Electronics systems has a rocker switch that provides the mains AC voltage to the controller.
This switch can get oxidation buildup over the period of many years and the result is that the DGCIII will not turn on.
That switch is no longer available, but this blog post will show you how to repair the switch and how to install a new switch if the existing switch can’t be repaired.
The power switch for the DGCIII comprises 2 sections that select the gain for the UHV, Bayard Alpert and extended ranges, and the higher current power switch section.
The power switch section is on the back end of the gang switch as shown in the picture below.
Step one is to remove the two screws that attach the power switch to the gang shaft. To do that, first unplug the power cord from the back of the DGCIII and remove the cover.
Remove the 4 boards that are inside the DGCIII. You do not need to remove the power supply board that is on the side of the DGCIII.
Use a small slotted screwdriver and remove the two screws.
Pull the power switch off the shaft.
Next, use a small screwdriver and lift the 3 tabs that hold the switch together.
Separate the back from the power switch mechanism.
Squirt some contact cleaner into the sides of the power switch and then use a needle nose pliers to rotate the flipper back and forth several times. Add some more contact cleaner and repeat. Remove any excess contact cleaner with a wipe and Q-Tips.
Use a meter and measure the resistance on the wires as shown in the picture below. When the flipper is to one side the contacts on the points shown below should have about 1 ohm of resistance, and they should be open going the other way.
If the switch checks out with an ohmmeter, then reverse the disassembly steps to reinstall the power switch section.
Replace the boards in DGCIII and replace the cover.
The DGCIII should turn on now when the power switch is turned ON.
If not, you can install a double pole single throw (DPST) panel switch in place of the rocker switch. You will need to drill a hole in the front panel of the DGCIII for the switch, and then move the wires over from the rocker switch section to the double pole single throw switch as shown in the above image.
Due to space limitations inside the DGCIII the DPST switch will need to be mounted sideways. In this case the new DPST switch will turn the DGCIII on and off, and the original power switch will still control the ion gauge selection which is typically UHV. Make sure that the DPST front panel switch can handle 5 amps @120 VAC or more. A typical DPST switch is shown below.
If you need your DGCIII to be repaired, please contact RBD Instruments here – https://support.rbdinstruments.com/portal/en/signin