M-2008-7-15
Standard Frequency Series Generators
Maintenance
15
Both filaments are lit. Remove
Collimator to confirm.
Transformer XS shorted to XL. With Prep depressed check
voltage from
XC
to
XL
and
XC
to
XS
.
HIGH MA
(continued)
Ground not proper.
Grounding must be EARTH GROUND. Neutral must be
connected to EARTH GROUND at incoming power supply.
Loose connections, defective ground rod or the absence of the
same will cause erratic exposures. Examples of symptoms are
terminating timed exposures too soon, causing the back-up
contactor to oscillate or “machine gun”. The Service Engineer
must understand that 0 VAC is
NOT GROUND
in X-Ray
Controls, it is only a reference for electronic circuitry attached
to A1.
M1 Feedback Circuit Defective. The M1 Feedback Circuit serves two
{2}
functions.
1. It allows sampling the current (MA) routed from the
High Voltage Output Winding back to the X-Ray
Control Terminal M1. Full-Wave Bridge Rectifier
AC Legs are in series with terminal M1 and allows
rectification of High Tension AC Current. The Full-
Wave Bridge rectifies this current to DC. DC current
measurements dc milliamperes (+) and (-) are taken
from (+) and (-) terminals on the Motherboard. After
the rectifier AC connections, the neutral circuit is
established to the neutral and EARTH GROUND
POST in the X-Ray Control.
2. The second and the most important function is to
provide a neutral High Voltage Return which is
connected to EARTH GROUND at the Main Power
Supply for the installation.
If you do not have a secure EARTH GROUND, if M1 circuit
has a loose connection or if the Thyrister on the high voltage
rectifier board is OPEN you may hear ARCING.
If you hear arcing, voltage may exceed ratings sending transits
throughout the X-Ray Control Printed Circuit Boards. The
transits will cancel voltage across timing capacitors and binary
counters resulting in the fault. ET at EI (Exposure Termination
at Exposure Initiation).
A Quick Test is to add a JUMPER from
M1
to GROUND Post on
the High Voltage Transformer. This bypasses the
M1
Feedback
and Meter Circuit. Check for LOOSE CONNECTIONS, OPEN
WIRES, DEFECTIVE TEST SWITCH or BRIDGE RECTIFIER
in MA Meter Circuit.
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