
Fault Isolation
Chapter Five: Maintenance
32
Power Supply
1. Measure the ±15 Volt supplies on the rear panel pressure gauge connector with respect
to P GND.
The voltages should be within the range of 14.8 to 15.2 Volts and the AC ripple should
be less than 10 mV peak-to-peak. If the voltages appear to be normal, then proceed to
check the next section. If supply voltages are incorrect, continue with the step 2.
2. Disconnect the pressure gauge and retest the supply voltages.
If the supplies now appear to be normal, the fault is with the pressure sensor. If the
supplies are not normal after removing the pressure sensor, continue with step 3.
3. Remove the power supply jumpers (E1-E2 and E3-E4) in order to isolate the power
supply from the rest of the PDR circuits.
If the supplies now are normal, the fault is probably a short circuit in the PDR circuits.
If the supplies continue to appear abnormal, contact MKS for assistance.
Pressure Signal Amplification and Readout
1. Set up the PDR so that it is displaying the output in mmHg from a connected pressure
gauge.
2. At the rear panel terminal block, connect an external voltmeter between Signal GND and
the Pressure Input.
If this voltage closely tracks
1
(±0.2 V) the voltage that is displayed on the front panel
DVM but is not representing the correct pressure, the pressure gauge is in error and the
PDR unit is operating normally.
If the voltage does not track, continue to troubleshoot the PDR unit.
To troubleshoot the signal path of the PDR-C-1C/2C, disconnect the pressure gauge and
replace it with two resistors connected in the following manner:
Note
If you have a PDR-C-2C, connect the resistors to Channel 1 and place
channel selector to Channel 1.
1
A voltage of above approximately 10.8 Volts will cause the digital panel meter to overrange and blank. This
is to be considered normal.
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