MKS 246C, Instruction Manual

Page: 79 / 92

Chapter Five: Maintenance and Troubleshooting Troubleshooting
69
Troubleshooting
The first approach when dealing with a problem with the 246 unit is to isolate the section of the
instrument where the fault lies. The 246 readout can be separated into the following sections:
•
Power Supply
•
Flow Amplifier String
•
In5 V Voltage Reference
•
Digital Panel Meter
•
Set Point Buffer and Flow Switching Circuit
When troubleshooting, it is always best to measure the power supply voltages first, since a
problem in the Power Supply will effect the performance of all sections. Therefore, it is
important to begin troubleshooting at this location. Jumpers are available on the Main PC board
to easily disconnect the supplies from other circuitry, if a faulty supply is discovered.
Power Supply
1. Measure the ±15 V supplies at the power supply jumpers on the PC board, or across
diodes CR2 and CR3.
The voltages should be within the range of 14.8 and 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 MFC from the 246 unit.
Should the supplies recover when an MFC is removed, then either the cable or the MFC
is defective. If the supply still fails, proceed to step 3.
3. Isolate the power supply jumpers from the circuits in the 246 unit by disconnecting the
±15 V power supply jumpers E3-E4 and E5-E6 and the 5 V jumper E1-E2, and measure
the supplies on the supply side.
Caution
Disconnect BOTH SUPPLIES to perform this test. Do not run the
circuits with only one supply operative.
If the supplies output the proper voltages, the problem lies with the 246 unit electronics.
If not, the supply itself is faulty. Contact MKS for assistance.
4. Test the 5 V supply at the jumper, or across diode CR1.
The voltage should be between the range of 4.9 and 5.1 Volts.
If the power supply is operating normally, proceed to Flow Amplifiers, page 70, to
examine the signal path through the channel amplifiers.