Preva Installation/Service Manual, 00-02-1577, Revision E01
90
voltage
Breakdown
High-voltage breakdown is characterized by a loud snap sound during an exposure
request.
1. On the Power Supply Board, measure the voltage across TP5, the Common
Return, and TP8, +350 volts DC, as shown in Figure 66. This voltage will be
acceptable if measured between 330 and 390 volts DC. Values above or below
this number indicate the need to replace the Power Supply Board.
2. If the voltage is correct, inspect the condition of the cabling between the Power
Supply Board, Logic Board, and Tubehead Assembly.
Of particular importance are the conductors held by the black connectors. These
conductors transmit the feedback values from the Tubehead Assembly and
directly affect the control of power to the Tubehead Assembly. Connections for
this cable begin with controls at J1 of the Power Supply Board and J4 of the
Logic Board. As shown in Figure 59, an internal set of connections will be
accessed below the distal side of the horizontal arm and at the inside top of the
Tubehead Yoke. The final set of connections is accessed by removing the Pivot
Cap located at the attachment point of the Tubehead to the Yoke.
3. If the cabling is found acceptable, select 1.5 seconds of exposure time, and
placing a DC voltmeter on TP8 or TP10, the Common Return on the Logic Board,
measure the feedback values at TP4 mA Monitor and TP3 kV Monitor, as shown
in Figure 67. Look for the following values:
• TP4 – mA Monitor. This voltage should be between 1.5 and 3.5 volts DC
during exposure attempts. The voltage should not oscillate between 1.5 and
3.5; instead the measurement should come to a specific value and stabilize.
Oscillating values or absent values will indicate the need to replace the
Tubehead Assembly.
4. TP3 – kV Monitor. This voltage should be between 3 and 4 volts DC during
exposure attempts. The voltage should not oscillate between 3 and 4; instead the
measurement should come to a specific value and stabilize. Oscillating values or
absent values will indicate the need to replace the Tubehead Assembly. If the
feedback voltages are present and stable, replace the Logic Board.
High voltage present.
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