As the 11-065s get older we are starting to see instances where the beam voltage, condenser voltage or objective voltage becomes unstable as the front panel potentiometers are adjusted.
The front panel potentiometers can become “noisy” as a result of oxidation on the internal contacts. In addition to causing instability in the output voltages, it is also possible for the potentiometer output potentiometer “open” up. When this happens, the output of the beam, condenser or objective supply can go as high as 6.4kV as shown in the picture below in which a 1000:1 high voltage probe is used to measure the beam voltage supply.
In the case of the condenser or objective supplies becoming unstable the result is that the ion beam might go in and out of focus, or the ion beam can get completely shut off. However, if the beam voltage becomes unstable and goes up to 6.5kV then the opto-couplers on the HV1 board will become damaged and then the emission or pressure circuits will no longer function properly. The opto-couplers are only rated up to 5kV.
If you suspect that your 11-065 beam, condenser or objective supplies are unstable, here is how to test the HV1 board outputs;
- Turn off the 11-065 and unplug the input power cord.
- Place the 11-065 on the bench and remove the top cover
- Remove the HV cover (on the right hand side of the unit)
- Unplug all of the spade connectors which connect the various wires to the HV1 and HV2 boards
- Lift out the HV2 board (the one closer to the center of the unit)
- Place all of the wires off to the side of the 11-065, making sure that none of them touch the chassis. Most of the wires are outputs and so have no voltage on them, but the 4 center wires on the HV2 board have 20VAC on them.
- Connect a high voltage probe to the beam output connector on the still plugged in HV1 board, (the board closest to the chassis) ground reference is the chassis. The outputs are: E93 Beam Voltage, E90 OBJ, E89 COND.
- Plug in the 11-065 input power cord.
- Make sure that the Beam voltage switch is OFF and the beam voltage knob is turned fully CCW.
- Turn on the 11-065 power.
- Turn on the beam voltage and monitor the output on the DVM that is connected to the high voltage probe.
- Slowly turn the Beam voltage potentiometer CW and observe the DVM reading. The Beam voltage output should increase smoothly from near zero to 5kV as you turn up the potentiometer. If you see jumping, instability, or if the Beam voltage output goes up to 6.5 kV then the potentiometer is noisy and needs to be replaced. The potentiometer is a 10 k ohm 5 turn 2 Watt 1% potentiometer available from DIgikey, Mouser and Newark.
- The OBJ and COND outputs go from 50% to 100% of the Beam Voltage. So to test those, the Beam voltage needs to stay fully CW at 5.0 The OBJ and COND potentiometers are also 10 k ohm 5 turn 2 watt 1% potentiometers.
If the Beam voltage potentiometer was noisy and the voltage went higher than 5kV, then the opto-couplers were likely damaged. If your do not get any emission current, then most likely U6 on the HV2 board was damaged and should be replaced. Other components may be damaged as well. If the emission works but not the pressure, U7 is likely damaged.
On the really old 11-065s, U6 was a TIL109 opto. When that part became obsolete about 20 years ago, it was replaced with a SPX314 opto. Most of the 11-065s in the field have been updated to the SPX314 (a modification is required). If you have a really old 11-065 with the TIL109 opto-couplers, RBD still has a few of those in stock.
Recently, the SPX314 has become obsolete and is hard to find. It can be replaced with a OPI 110 opto-coupler which is also has 15kV of isolation, so even if the HV1 board goes up to 6.4kV this opto-coupler will not get damaged. The OPI 110 will not only repair the problem, it will ensure that this particular problem does not happen again.
There is no modification required to switch from a SPX314 to an OPI 110, but the pin outs are slightly different and are shown in the pictures below.
The OPI 110 opto-couplers are available from most major electronic part suppliers including Mouser.
Here is a link to the datasheet – OPI 110 datasheet
If you need technical help to repair your 11-065 ion gun control you can contact RBD Instruments Inc. for assistance. We offer technical support, repair/ calibration and the use of a loaner 11-065 while your unit is being repaired.