My PKR stopped working during an experiment with an unstable plasma. My PSU blew a power output transistor. It is unclear which came first.
The PKR251 is a very useful gauge, this being an 'active, full-range' gauge, meaning it has both Pirani and magnetron gauges built in which automatically switch over at some defined pressure, and that therefore puts out a given voltage versus pressure for atmosphere down to 10^-9. Therefore, though I just scored two magnetron gauges off ebay for a song (and they seem to work too, always a bonus!!! But the chambers need a clean) the PKR251 is a king of gauges and so I am keen to fix it.
Here is the gauge before my disassembly, for those not familiar with these (the wiring is, obviously, my own as I do not have the specific connector for the pins):
I removed the chamber off the PKR251, which is a straightforward operation for routine maintenance. You are then left with a cap full of electronics. This is a 'non-repairable' item.. but as we know, anything is repairable with enough will!!
However, 'non-repairable' means 'one-way plastic clips' and it looked like I had to break the plastic frame up to get the bits out:
There are 3 layers of round boards that open out.
The part I suspect is indicated below. Reads 2.5 ohms, or so. Seems to be an ohmic resistance, no rectification or non-linearities. I can't quite make out the letters. Maybe that indictes it has overheated a bit?
Well, I'm looking to you chaps to tell me what you think, else I will be forced to use the 'brute' technique - apply the volts and let the high current flow until one of the components feels like it is getting hot!
Looks like it is that component, a cap and a voltage regulator parallel to that 2.5 ohms. I would presume the voltage regulator is hard to 48V for a few seconds, but the cap is likely vulnerable. Make your guess, and I'll desolder whichever is the odd-on for being faulty.