Chapter Five: Maintenance and Troubleshooting Troubleshootin
73
Troubleshooting
The first approach when dealing with a problem with the 247 unit is to isolate the section of the
instrument where the fault lies. The 247 readout can be separated into the following sections:
•
Power Supply
•
Channel Amplifiers
•
Internal +5 V Voltage Reference
•
External Ratio Amplifier
•
Digital Panel Meter
•
Set Point Buffer and Flow Switching Circuit
Since a problem in the Power Supply will effect the performance of all sections, it is important to
begin troubleshooting at this location.
Power Supply
1. Measure the ± supplies at the power supply jumpers on the PC board; reference to the
TP1 ground, located in the center of the Main PC board.
The voltages should be within the range of 14.8 to 15.2 Volts and the AC ripple should
be < 10 mV P-P. If the voltages are within range, proceed to step 4. If the voltages are
not within the acceptable range, proceed to step 2.
2. Disconnect the MFCs from the rear panel, one at a time.
Should the supplies recover when an MFC is removed, then either the cable or the MFC
is defective.
3. Isolate the power supply jumpers from the circuits in the 247 unit by disconnecting the
power supply jumpers and measuring the supplies on the supply side.
Caution
Disconnect BOTH SUPPLIES
to perform this test. Do not run the
circuits with only one supply operative.
4. If the power supply is operating normally, proceed to
Channel Amplifiers
, page 74, to
examine the signal path through the channel amplifiers.
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