Geiger-Counter miraculously stopped working after a few days

[bbccd]

Dear all,

I have just received my Geiger counter on monday this week. I had to build it on the same day, and since then it has been working flawlessly and I was very happy (having done my first step to detecting those usually undetectable types of radiation) - well, until today. This morning, I turned the switch to ON position - but no signals would come out.
I have replaced the batteries twice with fresh ones, and also inspected the device as good as I could (which essentially means optically), but the whole thing looks pristine - and there is no visible indication of any damage.
Unfortunately, I do not have a multimeter here at the moment, but then, I also wouldn't really know what to test for first.
I had a look in the forum and the wiki for indications what might be the problem, but to no avail. The thing was just sitting here in my warm room for a few hours (nobody except me had access to it) - nothing is known to me that might have happened to it -, but still, the thing appears to be dead!

So, my simple question is: can anyone of You give me some indications as to what to try? I want to bring it back to life! It does not simply seem to be the battery (I've tried completely new, fresh Duracell ones).

Looking forward to hear any suggestions!!

Best regards,
Björn

[mightyohm]

A couple quick checks:

When you turn the power switch on, can you hear a faint whine coming from the piezo speaker? You might have to put the speaker close to your ear to hear it (but watch out in case it BEEPS loudly in your ear!)

If you take a short piece of wire (or you can use your fingers if you're brave) and short the left side tube clip (J1) to the metal outside of the Geiger tube, does the counter click?

What do you have the HV adjustment set to? Any change in behavior if you adjust it?

Has anything metallic come in contact with the bottom of the kit?

[bbccd]

Hi, Jeff!

Thanks for Your quick reply!

I did the tests You have suggested. I do not hear any faint whine when putting my ear on the speaker when switching the thing on. I do not recall ever having heard anything like it when the counter was still working, but I might not have had my ear close enough anyways.
Also, I do not get a click when shortening the Geiger counter tube contacts.
The HV adjustment potentiometer is set to about 4/10 of the way, as before (the arrow shows to the "N" of "Bourne" on the labeling of that component). It is the setting that has worked before. I have tried to see if another setting helps (I turned the poti all the way from left to right), but to no avail. The HV setting on the poti doesn't seem to be the problem.

The counter was sitting an my desk all the time, and no metal or other parts can have touched the bottom. I have transported it a couple of times in the antistatic bag that the set parts came in. I am still waiting for the enclosure (which I have ordered separately), but for my testing so far, I have attached rubber feet to the bottom of the board to keep it from touching my desk (wooden desk). I do not see that anything metallic could have touched the base.

Any other suggestions? I am not sure what the problem may be. I was afraid that the Geiger counter may be the problem (e.g. due to a damaged filament), but since shortening it doesn't lead to clicks, I am now more afraid that the micro controller might be the problem. Any suggestions how to test that? Or other tests? Maybe simply one of the components on the board (e.g. a capacitor) may have been bad.

Thanks for any suggestions!
Best regards,
Björn

[mightyohm]

Try briefly shorting TP1 (the solder pad in the middle of the board labeled GM_PULSE) to ground. One convenient place to get ground is pin 3 of the PULSE connector, this is the pin all the way in the upper right corner of the board, next to the 'E' in PULSE. Or you can touch the wire to the spring terminal on the left side of the bottom battery, that is also ground.

Do you get a beep/flash now?

[bbccd]

Connecting the ground from the "Pulse" connector to the TP1 did not produce any beep, but when I connect the spring that goes to the "-" pole of the bottom battery (I believe this is the wire You were talking about) to TP1, I get a very short beep and LED pulse when I disconnect the cable again (but this doesn't always work - only about every second time; testing this a few times, this has a very weird way... the beep doesn't really come either when connecting or disconnecting the cable - it seems to be more related to the way how I take the cable away; if I take it away quickly, often nothing happens; if I scratch the cable a bit over the TP1 solder point, and then scratch it away from it, it seems to work better to create a beep... weird... could this be a sign of charging, spark creation or sth similar?).

Anyway, this is a good sign for the functionality of the micro controller, isn't it?

Any further suggestions what to test next?

[mightyohm]

Can you try the test again with the Geiger tube removed, to see if the results are any different?

The microcontroller does seem to be at least partially working, although you should get a beep every time you connect the wire (disconnecting the wire will also often result in a beep since the disconnection doesn't happen instantly). However, the fact that you did not get a beep from the PULSE connector is very strange.

If you haven't already, double-check your solder joints for any bad connections or shorts between pins.

Can you also double-check that you have the right transistors installed in the right spots?

Q1 should be the FJN3303F and the other two transistors should be 2N3904's.

Do you have access to a multimeter?

[bbccd]

Hi, Jeff!

Thanks again for Your quick reply!! Sorry for my late answer - this was a busy day!
I checked what You suggested. Removing the Geiger tube doesn't change the behavior during the test on TP1 (still only beeps - very shortly - when connecting to "-"-pole of lower battery, and no beep at all when connecting to uppermost pin of "PULSE" connector).
I inspected the solder joints, and they all look okay.
Also the transistors are all in place, and correctly placed. The one on Q1 is simply labelled "J3303F" (not "FJN3303F", as You wrote), but I suppose that that is alright (?).
I would have access to a multimeter in our lab, just don't have one at home right now.

Looking forward to further suggestions!!
Best regards!
Björn

[bbccd]

Hey, Jeff - dear All!

Quick addition to my previous post: out of desperation, I resoldered some of the solder joints, and that brought the thing back to life. I wouldn't say that those joints looked suspicious, but the board definitely was a bit hard to solder (some of the solder joints don't have any metal "padding" on the PCB, it is just the blank PCB, and that makes creating a "good" solder connection much harder).
Anyway, I am a bit surprised that it was so "easy". Didn't expect that.
So, for a second revision, I definitely suggest to add some metal padding to ALL solder joints, to simplify the process of soldering. Quite often with this board, the solder metal wouldn't want to stick to the component, but better to the soldering iron...

I hope that I could have helped others here, too...

Best wishes!
Björn

[mightyohm]

Bjorn,

In the next rev, I'm planning to resize some of the pads to make the kit a little easier to assemble.

Thanks for your feedback and I'm glad you got the kit working again.