APPLICATION NOTE NUMBER 4
Why don't I get mA readings?
We receive many Dynalyzer systems with a complaint of "No mA".
Most of these units work; occasionally we find real problems. In order for you
to complete your work, please check the following items:
1. Is the HVU plugged in? Is pilot light on?
- 2. What is the mA zero offset when the system is
connected? Is it within +\- 10 millivolts. Can it be zeroed? Zero it with a DVM,
while it is connected to the digital display. If the display is a Dynalyzer III,
use AUTO trigger and adjust the Rad and Fluoro zero's so that the mA reading
goes to about 0.1 mA, as zero is probably below zero. This procedure will
compensate for zero drift within the digital display.
- 3. Is the Tube anode high voltage connector
connected to the anode of the x-ray tube, and the Transformer anode HV connector
going back to the transformer? If they are reversed, the system will not work.
Never connect the anode of the HVU to the cathode circuit, or you will damage
the x-ray generator and or tube!
- 4. Check that the high voltage cable ground
shield is good. Often, it will snap at the termination. If both anode and
cathode cables are bad a very dangerous condition can result. Be sure the cables
are firmly plugged in, with the proper orientation. Is there filament current.
If the cables do not make contact in the cathode circuit, you will not see a
waveform in the FIL BNC. Only "CT" Dynalyzer measure DC filament
- 5. Measure the DC resistance between the
Dynalyzer anode Tube and Transformer HV receptacle common pins. ( Of course the
generator is not connected at this time.) There should be 200 ohms +/- 5%. If
you want to verify mA accuracy quickly, connect the + terminal of a 1.5 volt
battery to the anode Transf common pin, and the - terminal of the battery to the
anode Tube common pin. Connect DVM to mA output BNC. You should get .0075 volts
( 7.5 mV). In Fluoro range you should read 150 mV.
- 6. Check your BNC cables. Check HVU-display
interconnect for shorts and opens. pin A=cath, B=anode, C=ground, D=mA, E=fil,
F=mA range, G= mA ground.
- 7. Shake the HVU tank, and listen for tiny
screws or rattles. This is serious and requires disassembly for repair.
- 8. Is the mA power oscillator working? There
should be 10-15 v-pp at TP-1 of mA oscillator board ( on right side of HVU
behind front panel. Wiggle connector & filter cap.
- 9. When all else fails....send us your
equipment for checkup, calibration, and repair if necessary!