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  • October 13, 2016 at 11:11 am #3665
    wanek
    Participant

    hello!

    need some advice, please.
    i’ve assembled a new unit yesterday, (hw102, sw117).

    at first power up everything seems to be in order: the display, voltage, duty cycle, it connects to the internet, etc.
    BUT it keeps reading 0.0 pulses, no matter how long i wait. if i touch a metal object to the ends of the geiger tube it counts, as it were a radiation particle.

    i think that the software is ok. i suppose a defective geiger tube or some defective components in the circuit (the resistors and capacitors were verified one by one before soldering, so they should be fine). how can i debug this problem? there are “test points” in the circuit with predefined values?

    thanks!

    October 13, 2016 at 11:52 am #3667
    uRADMonitor
    Keymaster

    If the pulse counter works (touching the ends registers pulses), and there is high voltage on the 10M resistor going to the anode, than the tube is dead and you’ll need a tube replacement.

    October 13, 2016 at 12:17 pm #3668
    wanek
    Participant

    thanks for the fast reply!

    it depends what do you mean by “high voltage”. with my dmm i measured 190v dc between the anode and gnd. still, the display shows 380v. please see picture.

    October 13, 2016 at 12:19 pm #3669
    wanek
    Participant

    picture

    Attachments:

    1. problem.jpg

    October 13, 2016 at 1:55 pm #3671
    wanek
    Participant

    it’s not the tube! i have replaced with a known good one, and it is the same result…
    also replaced all relevant transistors, except mpsa42, nothing.

    i suspect the high voltage generator, maybe c6, c10, c11 or L1: if i heat them with a hair dryer, in several seconds the voltage drops to 300v and the duty cycle goes up to 90%, and stays there, even after the temperature goes back to normal (20c).

    on the other (working) unit, the duty cycle goes up quickly to 90% when heated, but the voltage stays around 360v. and after it cooled down to room temperature, the duty cycle goes down to normal (60-70%).

    October 13, 2016 at 5:46 pm #3672
    uRADMonitor
    Keymaster

    check voltage before the 10M going to anode, and GND.

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