Standard Frequency Series Generators
Maintenance
18
M-2008-7-15
7.9 TROUBLESHOOTING LOW MA
SYMPTOM
MOST COMMON
PROBLEM
HOW AND WHERE TO TEST
LOW MA
High Voltage Cables Too
Long.
Cable length is longer than the previous set used with the X-
Ray Control. Adjust filament resistors.
Incompatible X-Ray Tube.
X-Ray Tube filament characteristics may be incompatible
with present MA stabilizer and filament adjustments. You may
adjust voltage from
240 -250 - 260
at the MA stabilizer. Fine
adjustments may be made at each filament resistor.
Defective MA Stabilizer.
On PREP test from
A1
to
H3
. Voltage should be either
240
- 250 - 260
depending on where the stabilizer is strapped.
Any voltage less than
235 VAC
indicates a problem inside the
stabilizer.
Defective High Voltage
Cable. (Cathode side only)
Partial breakdown of the insulation in a High Voltage Cable
can cause lower MA’s at Higher kVp selections. As kVp is
increased to the point that it begins shunting minute current
across conductors MA starts to decrease. Technicians will
often increase the kVp further to compensate for the lower
MA only to realize that MA has decreased even further. You
should always install a
NEW
set of Cables just to eliminate this
possibility.
Defective High Voltage
Rectifier.
Test using a timed impulse counter at the X-Ray Tube. If the
Rectifier is half waving, half impulse count will be present.
Defective Leads or
Connectors in the High
Voltage Transformer.
It is unlikely that loose wiring is possible, unless the transformer
has been dropped. To test the High Voltage Rectifier Board and
wiring, remove the transformer from the tank and inspect all
wiring and connections using a OHM Meter.
Open Space-Charge
Primary Transformer
Open space charge primary may cause lower MA at lower kVp
and higher MA at higher kVp selections. Check Space Charge
Input and Output. Use schematics.
Defective Timer
Too low real MA/MAS versus indicated MA/MAS can sometimes
be caused by a malfunctioning timer, timer selector or the
ribbon cable connecting them. Test Timer with an impulse
counter.
7.10 TROUBLESHOOTING NO MA
SYMPTOM
MOST COMMON
PROBLEM
HOW AND WHERE TO TEST
NO MA
SCR’s shorted
If SCR’s are shorted the backup contactor will not come in nor,
can an exposure be initiated. Test Voltage from
J1-8
to
J1-10
on the Motherboard. If voltage is present and can be varied
changing kVp settings, you have a shorted SCR. Replace.
Anode and Cathode Cables
Reversed, Shorting out
Filaments.
Ensure Cathode Cable is connected to Cathode on the High
Voltage Transformer and to Cathode on the X-Ray Tube.
Anode
to anode, Cathode to Cathode.
If cables are reversed with
the anode of the transformer connected to the Cathode of the
X-Ray Tube. The filament output circuit is shorted. Immediate
indication would be
60 - 70 VAC
on FILAMENT PRIMARY,
when PREPPED. Measurements should be taken from
XC
to
XS
or
XC
to
XL
.
Defective Timer.
Timer is not initiating exposures. Observe... Is the Back-up
Contactor energizing? If it is, the problem will be OPEN SCR
HARNESS or
DEFECTIVE TIMER PULSE CIRCUIT
. If the
backup contactor is not energizing, test for a shorted SCR.
MA Stabilizer Defective.
Check output of MA Stabilizer
A1
to
H3
with PREP
Switch Depressed. Voltage should be
240 - 250 - 260
VAC.
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