voltage problem Geiger Counter

[bgrattan]

Hello,
I purchased a kit from Adafruit with SMB-20 and case. It seems to be picking up random radiation but the HV_Adjust doesn't seem to be doing anything--it works the same on both ends of the pot. I don't have a source to test it other than bananas which don't seem to do much.
Here are my voltage readings from new batteries (3.054 volts) Using a Fluke 87 III
U1 pin
1: 0
2: 1.59
3: 1.18
4: 2.91
5: 2.03
6: 0
7: .562
8: 3.054

Remove U1
4: .04
TP1: 2.95 (this seems off but maybe I'm not measuring it correctly--(ground to TP1)

TP2 to ground: adjusting HV with pot I get 167 -> 310 volts (no resistor being used)

Serial out from FTDI Friend:

mightyohm.com Geiger Counter 1.00
http://mightyohm.com/geiger
CPS, 0, CPM, 0, uSv/hr, 0.00, SLOW
CPS, 1, CPM, 1, uSv/hr, 0.00, SLOW
CPS, 0, CPM, 1, uSv/hr, 0.00, SLOW
CPS, 1, CPM, 2, uSv/hr, 0.01, SLOW
CPS, 0, CPM, 2, uSv/hr, 0.01, SLOW
CPS, 0, CPM, 2, uSv/hr, 0.01, SLOW
CPS, 0, CPM, 2, uSv/hr, 0.01, SLOW
CPS, 1, CPM, 3, uSv/hr, 0.01, SLOW
CPS, 1, CPM, 4, uSv/hr, 0.02, SLOW
CPS, 0, CPM, 4, uSv/hr, 0.02, SLOW
CPS, 0, CPM, 4, uSv/hr, 0.02, SLOW
CPS, 1, CPM, 5, uSv/hr, 0.02, SLOW
CPS, 0, CPM, 5, uSv/hr, 0.02, SLOW
CPS, 2, CPM, 7, uSv/hr, 0.03, SLOW
CPS, 0, CPM, 7, uSv/hr, 0.03, SLOW
CPS, 0, CPM, 7, uSv/hr, 0.03, SLOW
CPS, 0, CPM, 7, uSv/hr, 0.03, SLOW
CPS, 0, CPM, 7, uSv/hr, 0.03, SLOW
CPS, 0, CPM, 7, uSv/hr, 0.03, SLOW
CPS, 0, CPM, 7, uSv/hr, 0.03, SLOW
CPS, 0, CPM, 7, uSv/hr, 0.03, SLOW
CPS, 1, CPM, 8, uSv/hr, 0.04, SLOW
CPS, 0, CPM, 8, uSv/hr, 0.04, SLOW
CPS, 1, CPM, 9, uSv/hr, 0.05, SLOW
CPS, 3, CPM, 12, uSv/hr, 0.06, SLOW
CPS, 0, CPM, 12, uSv/hr, 0.06, SLOW
CPS, 0, CPM, 12, uSv/hr, 0.06, SLOW
CPS, 0, CPM, 12, uSv/hr, 0.06, SLOW
CPS, 0, CPM, 12, uSv/hr, 0.06, SLOW
CPS, 0, CPM, 12, uSv/hr, 0.06, SLOW
CPS, 1, CPM, 13, uSv/hr, 0.07, SLOW

Could anyone comment on this? Maybe it's ok but I want to be sure. Thanks in advance.

Bob

[mightyohm]

That all sounds fine. If I measure the HV test point with my Fluke 87 V alone (no resistor), I measure about 215V. This is when VR1 is properly adjusted for 400V as measured with a Gigaohm resistor in series with the DMM.

[bgrattan]

Thanks, Jeff, if it looks good to you then I must be ok. Now I need to find a source of radiation to make sure I’m picking things up as I should. I’ll adjust my HV to 215 to agree with yours. Much appreciated and a very nice kit!
Bob

[MarkDV]

Explain how to adjust the voltage exactly 400 V using a multimeter? What is the measurement scheme? Need a high resistance resistor? How to connect it?

I am sorry for my English!

[mightyohm]

There's some information here:
viewtopic.php?f=15&t=487

[MarkDV]

Thank. But the link does not work! http://ea4eoz.ure.es/hvprobe.html

[mightyohm]

There is an archived version of that page here: https://web.archive.org/web/20120626122 ... probe.html