Midmark Preva - Page 97

Preva Installation/Service Manual, 00-02-1577, Revision E01
94
Incorrect
mA
At times, various measurements of an otherwise fully functional system indicate that
milliamperage may be incorrect. Milliamperage [mA] is controlled by the
microprocessor and is not adjustable. The Preva generates milliamperage by first
establishing a reference voltage and then comparing the feedback voltage to the
reference. Follow these steps to establish proper operation of the mA controls.
1. On the Logic Board, place a voltmeter on TP8 or TP10, the Common Return and
TP2, mA Program, as shown in Figure 67. Compare measurements to the
following chart (volts DC).
60 kV
65 kV
70 kV
4 mA
3.1
3.4
3.7
5 mA
3.2
3.5
3.75
6 mA
3.3
3.8
3.8
7 mA
3.4
3.7
NA
2. To evaluate the feedback voltages which represent the measured mA within the
system, refer to the table below; select 1.5 seconds of exposure time and
measure the DC voltages during the exposure only. This measurement is made
across TP8 or TP10, the Common Return, and TP4, the mA Monitor, as shown in
Figure 67.
Volts DC
4 mA
2
5 mA
2.4
6 mA
2.9
7 mA
3.4
Values which approximately match the above tables represent a correctly operating
system. Other values may indicate that boards need to be replaced. Further
assistance can be obtained from Midmark Technical Support.