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Shonky
United Kingdom
4 Posts |
 Posted - 09/21/2025 : 05:34:03
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Hi I'm new here, great forum.
I just bought my first geiger counter, a second hand GMC-300s from fleabay and there's something going on which doesn't make sense.
I'm getting background readings mostly between 25 and 35 CPM but 0.00 on the microsieverts/h and the mR/h.
Even with a handful of old thorium mantles, which got the thing clicking away quite merrily, there were only zeros from the dosage settings after an hour.
I think it's a dud but just wanted to check whether I'm missing anything?
Many thanks |
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| Reply #1
3z_phoenix
7 Posts |
Posted - 09/22/2025 : 03:01:11
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hi Shonky,
for me, this sounds like "lost" calibration-data, bcs.
some math is used to convert the CPM-value into microSivert per hour.
please have a look into "initional settings", if you can find something
like "Tube calibration" the value there must exist and no Zero-value.
sorry, i only have a GQ-GMC-500+ and i am not sure what Tube are used
at your device...
but sure our EmfDev will take-over so he read about your problem...
meanwhile i try to study the hardware details about your device...
kind regards, 3z_phoenix |
[first rules from my survival-handbook]
1. ...the difference between democracy and anarchy are 3 canceled main meals ~ONLY~
2. ...better have it - but not need, as need it - but not have!
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| Reply #2
3z_phoenix
7 Posts |
Posted - 09/22/2025 : 04:16:09
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yes, i do RTFM :)
pls. open main menue there u find "Init Setup" select this
there u find "Factory Reset"
pls. select this, it should load back all manufacturer defaults
check again with your radio-sources
if still stay the same problem
over this "Factory Reset" u see "Calibration" for check the Values
there not have to be Zero-Values...
in hardware description i found:
High sensitivity tube M4011 installed (user can remove this tube install other tube if needed)
its the same Tube, like my GMC500+ use,
i can give u my calibration values :)
i only worry abit about "a User can remove this tube and install other" bcs. as u wrote your device had a pre-owner...
...hopefully we can get this device back into complete running...
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[first rules from my survival-handbook]
1. ...the difference between democracy and anarchy are 3 canceled main meals ~ONLY~
2. ...better have it - but not need, as need it - but not have!
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| Reply #3
Shonky
United Kingdom
4 Posts |
Posted - 09/26/2025 : 01:02:18
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Thank you 3z phoenix, and sorry for being so slow to reply, I've been away.
Your answers were very helpful thank you but I haven't found any solution thus far.
I've reset to the factory settings but there's no change unfortunately, and calibrate 1, 2 & 3 all show zeros for uSv/hour and mR/h (though the CPM has values).
If you could let me know the calibration values for your tube I'd be very grateful.
Many thanks again |
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| Reply #4
Shonky
United Kingdom
4 Posts |
Posted - 09/27/2025 : 01:03:23
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Hi All,
anybody else got any ideas?
Is there somewhere where I can find information that would allow me to try to sort this out on my own?
Many thanks in advance |
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| Reply #5
Shonky
United Kingdom
4 Posts |
Posted - 09/27/2025 : 11:19:49
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Hi again,
I've decided to send the unit back so please don't anybody spend any more time on this.
Thank you very much for your help 3z, though it didn't completely solve the original problem, it did get me to where I needed to be.
Much appreciate your time and effort. |
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| Reply #6
3z_phoenix
7 Posts |
Posted - 09/30/2025 : 23:25:19
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hi Shonky,
you are all time welcome :)
well, if also a factory-reset did not bring back the default calibration-values,
that realy point into a defective hardware :(
Youre decision is best in try to reject the deal,
i keep my thumbs under pressure for your success.
kind regards, 3z_phoenix |
[first rules from my survival-handbook]
1. ...the difference between democracy and anarchy are 3 canceled main meals ~ONLY~
2. ...better have it - but not need, as need it - but not have!
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Topic |
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Zero dose readings
