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

Model 99 ABS Current Preamplifier no signal problem

The Model 99 Current Preamplifier is used on the older PHI (Physical Electronics) 660 scanning Auger electron spectrometers.

99 ABS preamp

There is a fairly common problem with this design of preamplifier where the input JFET can get damaged from sample arcing which results in a total loss of ABS (absorbed current) image.

The most common solution to this issue is to replace QN2 which is a 2N5546 dual JFET. These parts are obsolete but readily available on Ebay. You can also find equivalent replacement JFETs such as the EXR461.

To replace QN2, first remove the cover from the 99 ABS preamp.

The picture below shows the location of QN2.

Use a tweezers to pull up each leg of QN2 as you heat it with a soldering iron and then use a solder sucker or copper braid to remove all the solder from the holes on the circuit board.

Note the location of the tab that is on the circuit board and then bend the leads on the replacement 2N5546 so that the leads line up with the holes in the board. Press the 2N5546 down so that the pins are firmly in the holes, then remove the 2N5546 and cut the ends of the leads so that they are shorter. You only want about 1/8″ of the leads going into to the holes as otherwise the leads might short to the chassis.

Insert the 2N5546 into the holes and solder the lead wires to the board.

Replacing QN2 will likely restore the ABS image.

The schematic below shows that QN2 is the first thing that sees the input signal and so it makes sense that QN2 would likely be damaged from an arc. Also, JFETs are susceptible to arc damage more than a lower impedance device such as an op amp.

For help with repairs or maintenance on your PHI 660 (or other older PHI surface analysis systems) please contact RBD Instruments here – https://rbdinstruments.com/contact.html

Replacing the stage brakes on a 15-630 Specimen stage

The 15-630 Specimen Stage is used on Perkin Elmer Physical Electronics 600 and 660 scanning Auger systems.  The 15-630 is a precision sample stage that has micrometers for the X, Y, Z, tilt and rotation axis.  The gear ratio is high in order to have precise small movements. To lock the positions into place, spring loaded .120” diameter high temperature plastic rods are employed. With use, these brakes wear down and the micrometers no longer hold the stage axis in place which in turn causes drift at higher magnifications.This blog post will show you how to replace the stage brakes.

Stage brakes for 15-630 specimen stage

The PHI (Physical Electronics) part number for the stage brakes is 605857 and as of this posting they go for $6.00 each.

To determine whether or not the stage brakes need to be replaced on a micrometer just move the micrometer a turn and see if it feels loose or slightly snug. If you can easily turn the knob back and forth then the brakes are worn out and need to be replaced. Usually only one or two micrometers need to have new stage brakes. But if you have never checked this before you may find that they are all loose and need to be replaced.

You will need to remove the knurled knob on the micrometer in order to replace the stage brakes. Before you attempt to remove the knurled knob, you will need a 183-6 Bristol wrench. You can get those from Bristol at this link –


But, since the original Bristol was sold a few years ago, the new Bristol sells the wrenches in packs of 10 minimum. So if you do not have a 183-6 Bristol wrench handy you can also use a 5/32″ Allen wrench.

Hold the knob firmly and press it towards the center of the stage as you turn the cap head screw that is inside the center of the knurled knob CCW until the screw is loose. Then, very slowly, pull the knurled knob off.

Z axis micrometer

There are some springs inside two small holes that provide pressure on the two stage brakes. If you pull the knurled knob off quickly then the stage brake and possibly the spring will go flying.

Remove knurled knob

Remove the worn stage breaks and insert the new ones into the holes.

Remove old stage brakes

Replace the knurled knob and insert the cap head screw. Hold the knurled knob firmly and press it in towards the center of the stage as you tighten the cap head screw.

Repeat this process for all of the micrometers that need new stage breaks.

Adjust indicator position

Each micrometer has an indicator that shows where the micrometer is in relation to the min and max movement for that micrometer. For example the Z is from +5mm to – 15mm.

To change the indicator, with the knurled knob off remove the shaft gear.

remove shaft gear

Next, spin the indicator gear until you have the indicator to the desired position. Then replace the center gear.

spin indicator gear

The Z axis indicator may need to be adjusted once in a while as it can slip. You can sent the actual Z position of the stage to as low as it will go and then set the indicator to -15mm. You will know that the Z indicator is off if you are having trouble loading your sample or getting the stage close enough for an elastic peak.