Fusor Forums

I have a Canberra 2005 scintillation preamp that I just received, it appears that one of the capacitors on the input side and one of the large resistors on the power input are destroyed. Does anyone have the schematic diagram with component values? The brochure from Canberra on this preamp only has a generic schematic without component values.
Thanks,

David

These components are not part of the pre-amp in a critical sense. The capacitor is a filter for one of the input voltages and the resistor is designed to burn out if the capacitor shorts while in use. The resistor protects the NIM power supply feeding the pre-amp.

Such resistors can be 1 to 10 ohms, normally. The filter capacitor can be most any value, but is typically a tantalum capacitor between 10 and 47 ufd.
The voltage rating should be at least 30-50 volts if shooting blind with no schematic.

Richard Hull

Hello Richard,

i found a schematic for a Canberra 2004 preamp, looks like this board was also used for that module. What I thought were resistors are actually 1 miliHenry inductors, they sure look like resistors. The capacitor appears to be polarized, 0.01 uF at 5KV. Not sure if these are electrolytic or tantalum. Here is the link for the schematics. It also looks like they combined some of the transistors into an IC package in the 2005. Now to find these parts and test the preamp. It also looks like this publication has a fair amount of information on fixing the Canberra 35 plus MCA, which is another instrument I am in the process of getting running for gamma spectroscopy.
www.pub.iaea.org/MTCD/publications/PDF/te_426_web.pdf

funny your link gives this


This site can’t be reached
www.pub.iaea.org’s server IP address could not be found.
Go to http://www.iaea.org/
Search Google for pub iaea org MTCD publications PDF 426 web
ERR_NAME_NOT_RESOLVED

you see those blue capacitors each side at the top of the pic
replace them with low esr 105 degrees C electrolytic caps those bead tantalums are a short wanting to happen.
I do this on all NIM modules that come into my area at work dead
They go out alive and none have come back in the 15 years ive work there

Sorry about the bad link, this one should work:

https://www-pub.iaea.org/books/IAEABook ... nstruments

Thanks for the advice on the capacitors.

The inductors serve a dual purpose. Just like resistors, they are in the power lines of the board. They are there to blow out on overload due to shorted capacitors and to squelch high frequency pulses from entering via the power supply lines. Thus, they are fuses when things go high order and pulse filters when they are not burning out.

John is correct....Get rid of all tantalum caps! NIM modules tend to use 1/8 watt, 10 ohm fusible resistors. These are smoked in half in many modules. Every power line on most NIM boards have these and a matching tantalum or two or three scattered along the power trace on the board. Replace the resistors and gut all tantalums in power lines. Replace the caps with a high grade modern electrolytic rated for high temp operation....Again, as John has already noted. Like john, I have fixed a nice sized pile of NIM modules that had no problems at all other than shorted "tants" and blown 1/8 watt resistors.

Richard Hull

Thanks for all of the advice, I have been ordering the needed components. Any guesses on the current rating for the 1 mH inductor that is burned out on this preamp?
Thanks,

David