DGCIII Power Switch Fix

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.

DGCIII power switch

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.

ON OFF rocker switch

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.

Removing rocker switch section

Pull the power switch off the shaft.

Next, use a small screwdriver and lift the 3 tabs that hold the switch together.

Pull up on the 3 tabs

Separate the back from the power switch mechanism.

Remove back of rocker switch

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.

Contact cleaner
Put contact cleaner in here
rotate contacts a few times

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.

Switch locations

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.

DPST panel switch

If you need your DGCIII to be repaired, please contact RBD Instruments here – https://support.rbdinstruments.com/portal/en/signin

DGC III Filament Select Relay

The DGC III ion gauge controller (also called the DIG 3) used on many of the older PHI surface analysis systems can operate 2 ion gauges (only one at a time). There is a relay inside the DGC III that puts the filament current output to the ion gauge connectors on the back of the DGC III. Normally there is only one ion gauge on the vacuum chamber and it is plugged into the Ion Gauge 1 connector (normally closed) on the back of the DGC III. The relay is shown in the photo below.

DGC III filament select relay

If your DGC III does not read correctly, you can first check the +/-12V and +5V power supplies. Here is a link to some information on how to do that – DGC III power supplies test. If any of the power supplies are low and have a high AC component, then usually that issue is caused by a leaky capacitor on the power supply board. ** CAUTION! Make sure that someone who is trained on working safely with voltages up to 500V performs the voltage measurements. There are potentially lethal voltages inside the DGC III.**

If the power supplies check out OK then it is possible that the filament select relay is dirty. To test that, make sure that the DGC III is OFF and then move the black filament cable on the back of the DGC III from filament 1 to filament 2. You do not need to move the COL BNC cable as those are both tied together.

Turn the DGC III back on and press the 2 button. That will select ion gauge 2. Press the I/T 3 button to measure the vacuum and see if the DGC III works normally. If it does, then the filament select relay is dirty. You can just keep the ion gauge connected to ion gauge 2, or, you can clean the relay and connect the ion gauge back to ion gauge 1.

To clean the relay, make sure that the power is OFF to the DGC III and if not already down, pull the unit out of the rack and remove the cover.

Pull the relay out and remove the 4 screws on the bottom of the relay.

The contacts that are touching are the normally closed ion gauge 1 contacts. Use a small strip of some very fine emery cloth or sandpaper to gently clean the contacts on both sides. Then, use a small strip of paper with some isopropyl alcohol on it to remove the leftover grit. Replace the cover on the relay and reinstall the relay.

Ion gauge 1 should work properly now but if not you can order a new relay from companies like Grainger or Mouser. Just make sure that the pins match schematic that is on the side of the relay. Google 105 3PDT 10A relay and you will find it.

If your DGC III does not work and you need some help or a loaner, please contact RBD Instruments for assistance.