11-065 Ion Gun Control no high voltage

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Over the years I have seen this problem a few times and thought that it would be worth mentioning.

The symptom is that there is no high voltage on the 11-065 ion gun control HV1 board, or the voltage is low.

11-065 Ion Gun Control

11-065 Ion Gun Control

On the system, the symptom will  be no or low target current.

If you have this problem the first thing to check is whether or not C5 on the HV1 board is blown out.   It is an electrolytic capacitor and these days most electrolytic have some creases in them which allow the capacitor to expand and release gas and fluid when it fails.

HV 1 board in 11-065

HV 1 board in 11-065

The location of C5 on the HV1 board is shown below.

C5 location on the HV1 board in an 11-065

C5 location on the HV1 board in an 11-065






For a recent 11-065 repair the symptoms  were no high voltage on the beam and the COND was low. C5  on the HV1 board was obviously blown out so I replaced it.   However I still did not have any high voltage on the beam, and the COND voltage was also low.

The resistors, capacitors, diodes and transorbs on the HV1 board all checked out fine.  It was then that I remembered I have seen this problem once or twice before.   What happened is that when the C5 capacitor failed some of the electrolytic capacitor fluid seeped onto the board.  It was not really noticeable, but there was enough electrolytic capacitor fluid on the board to effectively add a high resistance to the board surface and load down the high voltage supplies.

The schematic for C5 in the filament circuit is shown below.

HV1 board schematic C5

HV1 board schematic C5

The solution was to clean the board with a diluted mixture of Alconox detergent and a tooth brush then rinse the board thoroughly in warm water.  Avoid wetting the transformers.  Blow the HV1 board dry with compressed air and then use a heat gun on low to completely dry the board.

After cleaning all of the electrolytic fluid off and drying the board everything worked fine.

Keep this in mind with any electrolytic capacitor failure where the capacitor blows out and  leaks on the board.


If you need to check the drive transistors on the heat sink, they are shown below.


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1 thought on “11-065 Ion Gun Control no high voltage

  1. A seriously contaminated board or assembly can be clean and rinsed aggressively with Alconox or similar. This will almost certainly leave residual moisture in places (like transformers) where it does not belong. The assembly can be baked to a temperature that will drive off all moisture but this will thermally stress some components. The solution is to bake at a safe temperature (80C is usually ok) and then use vacuum to finish the job. One to ten torr after an 80C soak is very thorough.

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