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3. Measure at T2 pin 3, this point will be variable depending on the position of the
output control knob. At the full counter-clockwise position this voltage will be less
than 3 volts AC. At approximately ½ output turning clockwise this voltage will be ½
line voltage. If not present, check the neutral connection to the variac, if this
connection is present replace T2.
4. Check at the terminal block adjacent to the high voltage transformer T1 at the orange
wire for the same AC voltage starting with the output control to full counter-
clockwise position then at ½ output. If not present, see the section on the Zero Start
Interlock does not engage.
5. Locate the secondary T1 high voltage transformer wire connected to D3 anode on the
Stack board and disconnect. Connect a P6015A high voltage scope probe or
equivalent to the T1 secondary wire with the probe negative lead connected to chassis
ground. See the volts/div on the oscilloscope to 2 volts and the timebase to 5ms.
Turn the output control approximately to ½ output. This measurement should be
14kV AC peak to peak.
6. Verify that all other primary and secondary wires of T1 are connected to their
respective destinations with a digital multimeter. Ensure that power is off and
disconnected when making these measurements. If measurement in step 5 is not
present and all connections are verified, then replace the high voltage transformer T1.
7. Reconnect T1 secondary wire and lift D3 cathode on the Stack board. Connect the
P6015A probe to this point with the negative lead to chassis ground and turn output
control to ½ output. Set scope settings to the same as in step 5. This measurement
should be approximately 7kV AC with the negative portion clipped by the diode. If
not present replace D3 on the Stack board.
8. Check the SCR cathode to anode resistance for Q1-Q10. Ensure that the power is off
and disconnected. These measurements can be obtained by measuring across R1
through R10. Replace any SCR' s that are shorted. Good measurements will be 70K
ohms or higher while defective SR' s will have much lower readings.
9. Check continuity of test leads 1, 2, and 3 back to the selector switch, replace any
found to be open.
10. Check continuity from the ground lead alligator clip to the Discharge board ground
stud. If open, replace the ground lead.
11. With a 10X scope probe measure at pin 32B on the I/O board with the negative probe
lead connected to chassis ground. After engaging the zero interlock turn the output
control to approximately ¼ output. Set the oscilloscope to 1 volt/div and 10µS sweep
rate. The signal at this point should be about a 1.8-volt surge waveform. If not check
continuity with the tester AC input disconnected from P1 pin 32B & 32C on the I/O
board to J1 pins 3 and 4 on the Discharge board.
Baker Instrument Company
The Measure of Quality
16
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