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 GQ Geiger Muller Counter
 No counts on GMC 300
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gazinbali

Indonesia
4 Posts

Posted - 02/24/2017 :  04:36:24  Show Profile  Reply with Quote
Hi..
I have had my 300 for several years.. It used to work fine.. but has been sitting in a drwaer for years with no battery.
Recently I decided to se what was happening with it, and installed a new battery. After it came to life I nticd the right hand side of the display incl the battery level meter display is faded..but more important is zero clicks.
I dont have a test source, so cannot check or calibrate.
I tried testing the tube voltage, but the only meeter I have is an el cheapo yellow china digital version with max 500V DC range.
On that setting i get zero v on the tube??
Is there a circuit for this item, or are there some test points on the back of the board I can check.
While testing.. I noted it will count clicks when I touch the Multimeter probes.. I can make it count up to the alarm level of 100 and the alarm goes off. This actually shows the device is working.. but maybe the tube is not. Its had very little use..??
Is it likely its working and I really do have a zero BG radiation??
or is there some problem?
I did a factory reset, but no change.
Hope someone can comment soon , would be good if you can reply to my e mail below.
Thanks
Gary in Bali
Contact me here
Reply #1

Distelzombie

Germany
160 Posts

Posted - 02/24/2017 :  05:06:29  Show Profile  Reply with Quote
Hi.

I don't know much about the electronics. But the cheapo multimeter should be enough. It should read about 180V at the tube if the device is working correctly.
Also:
quote:
Is it likely its working and I really do have a zero BG radiation??
or is there some problem?
Unless you live 2,150 feet below the earth's surface in the Waste Isolation Pilot Plant in New Mexico or in the Sudbury SNOLAB, definitely no. (SNOLAB has some low radiation experiments too)

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.

Edited by - Distelzombie on 02/24/2017 05:15:00
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Reply #2

quant8

Singapore
1 Posts

Posted - 04/12/2017 :  18:48:37  Show Profile  Reply with Quote
I am in the same boat, everything lights up, but no count or clicks. Nothing broken inside, but cleaned up the M4011 geiger tube contacts anyway - no effect. Operating voltage across the tube was 160VDC. Found the trimmer and adjusted to max - 170+v, no effect.
In my case it might be the driver failing to bias the tube to a sufficiently high operating potential. The detection electronics seem to work ok, since there is a click and a count whenever I touch and remove the meter probe (thus causing a small impulse). A new tube will cost me close to US$50 including shipping.
Anyone know if 160v (across the tube terminals, with tube connected) is sufficient to at least generate a count? The tube's resistance, with the device powered off, is too high to even register on my Fluke179DMM, so I don't think it's shorted.

Peter
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Reply #3

Distelzombie

Germany
160 Posts

Posted - 04/14/2017 :  08:14:37  Show Profile  Reply with Quote
I looked in a bay and the original M4011 tube goes for 30 while the SBM-20 goes for 15-20.
The latter tube is even slightly more sensitive, if I remember correctly.

GMC-300E+ V4.20 with sbt-11 alpha tube

My statements are to be taken as stuff-a-hobbyist-says.

Edited by - Distelzombie on 04/14/2017 08:15:09
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