Geiger Counter Problem

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Geiger Counter Problem

Postby Chronosock » Sat Jul 21, 2012 5:50 pm

So I cant seem to get my Geiger counter to work properly after much re-soldering and double checking the direction of the transistors and diodes. The strange thing is is that it passes both grounding tests by shorting GM_PULSE to pin 3 of the PULSE connector and to the spring on the left corner of the battery, but it does not pass the test to short the tube clips. What is even stranger to me is that the LED will light and the speaker will beep intermittently if I tap the negative clip with my copper wire that i used for shorting, but both the LED and speaker never go off when the wire is also touching the positive clip while tapping the negative clip. This happens regardless of the presence of the tube or not. I also do not hear a whine from the speaker while it is on, and turning VR1 doesn't seem to affect any of this,if that helps at all. Any suggestions? Thanks in advance.
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Re: Geiger Counter Problem

Postby mightyohm » Sat Jul 21, 2012 11:06 pm

It sounds like the HV supply isn't working. Have you checked to make sure that the transistors Q1 and Q3 are in the right spot?

Is U1 (the 555) installed the right way and pressed fully into the socket, with no bent pins?
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Re: Geiger Counter Problem

Postby Chronosock » Sat Jul 21, 2012 11:27 pm

Just checked Q1&3 again and both are correct, then I took out and re-seated U1 in its socket, no bent pins when taking it out and putting it back in. It is also in the correct way, notched side corresponding with the diagram on the plate, and the small dot towards the notch, according to the picture on the front page for it. The Geiger counter now fails both grounding tests, but it did make a short beep when i touched the GM_pulse node, without connection to anything else.
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Re: Geiger Counter Problem

Postby mightyohm » Sat Jul 21, 2012 11:37 pm

Which grounding tests is it failing?

Still no faint whine from the speaker? If you connect a digital multimeter from TP2 to ground (PULSE pin 3), what do you measure?
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Re: Geiger Counter Problem

Postby Chronosock » Sun Jul 22, 2012 12:07 am

For whatever reason it now passes the grounding test from TP1 to both PULSE pin 3 and the spring, probably from my poor wire positioning when trying to short them, but still fails to get a response from J1 connecting directly to J2 via the copper wire I had and the multimeter. Unfortunately I only have an analog multimeter, but from TP2, it registers nothing. To make sure my multimeter was working I tested from TP1 to the PULSE pin again with it, and that made the needle move and also made the speaker and LED activate. There is also still no whine from the speaker.
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Re: Geiger Counter Problem

Postby mightyohm » Sun Jul 22, 2012 12:37 pm

Check all of the components on the left side of the board (the high voltage side) for correct value and polarity. Also triple check the board for bridges and cold solder joints. If you send me a good high resolution, well lit photo of both sides of the board I can take a look also.
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Re: Geiger Counter Problem

Postby Chronosock » Fri Aug 03, 2012 8:18 pm

Sorry this took so long, but here is the front and back pictures of my assembled Geiger counter.

Front: http://i.imgur.com/GG4yV.jpg
Back: http://i.imgur.com/POqYR.jpg
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Re: Geiger Counter Problem

Postby mightyohm » Fri Aug 03, 2012 10:47 pm

It's hard to tell from the photo, but I don't think U1 is inserted all the way. Use a tiny screwdriver to pry it out of the socket, check to make sure the pins are straight, and then reinsert it again and push it all the way into the socket.

I also see one bad solder joint on the bottom, it's the left terminal of C2 (as seen from the bottom side of the PCB). Inspect all of your solder joints closely and make sure you have a good hershey-kiss shaped blob of solder on each lead, that completely surrounds the lead and covers the pad. Also double check to make sure there aren't any short circuits between any of your solder connections - little bits of solder or metal bridging the gap between the pads.
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Re: Geiger Counter Problem

Postby Chronosock » Sat Aug 04, 2012 7:00 pm

Re-set U1 into its socket and made sure it was sitting in all the way, then redid C2 and a couple others on the HV side, and unfortunately, still nothing from that side and no whine from the speaker, I think I'm running out of options.
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Re: Geiger Counter Problem

Postby mightyohm » Sat Aug 04, 2012 8:49 pm

Hi,

Do you have access to a digital multimeter?

I may be able to give you some more voltages to check on the PCB, but you'll need a digital multimeter of some kind.
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