AGS - Service Notes

Service Note No: 10
To: Maintenance staff
Subject: Mass Flow Controller Trouble-shooting Guide

Problem: A number of customers have reported trouble with the MKS 1200 series of MFC's (model 2259). We have found that, in most cases, the MFC simply requires a field adjustment and does not require further servicing. The problems include oscillations, can't control to setpoint, can't zero, and intermittent troubles. The oscillation problem was discussed in SN 09. This new service note will give a troubleshooting primer that should help you to determine if an MFC requires a simple adjustment or if it must be removed for service.

Solution:
WARNING: This technique is only to be used by a technicians qualified to perform service tasks on the System 1000/1700 by A.G.Services. We do not advise that you attempt to service plasma systems unless you are qualified to do so. Finally, A.G.Services assumes no liability for the use of this procedure. It is presented only as guideline and for informational purposes only. If you need expert assistance to solve problems with your system, feel free to call A.G.Services.

Check Setup - If you suspect an MFC is not operating correctly, first check the gas source bottle and make sure that all the proper valves are open and that the outlet pressure is set to 15 PSI (+/-3). Next, verify that the CDA (compressed air) pressure is 80 PSI (+/- 5). It is also a good idea to check the power supply voltages are as follows: 24-29 VDC, +/-15.00 VDC (+/-.05).

Zero MFC - Once you have verified pressure and power are in spec, check and adjust the MFC's zero reading (caution: do not adjust the zero if the MFC has been used in the last 60 minutes or an erroneous adjust may occur - insure that there is NO flow through the MFC).

Operational Check - To perform the check: enter a setpoint of 50% for GAS X (where X = MFC in question), manually rough the system down and then press manual GAS X to activate the MFC in question. The flow should go from 0 to 50% within a second or so. Verify that the flow is stable for at least 1 minute. Next, try a setpoint of 95% and finally try the MFC at 5%. If the MFC operates at all three of these setpoints with stability, it is working within MKS specifications. If any MFC should fail this test, proceed to the applicable paragraph below for further instructions.

Oscillations - Click on Service Note 09 for further details.

Can't flow below a certain level - If you enter a setpoint and the flow reading will not respond, try a lower setpoint. If it does not respond, try a higher setpoint. If the MFC will not control but shows flow (or over range "---.-") when on but goes decreases when shut off , the valve seat is too far from control valve plunger: Adjust valve seat as required. Click on Service Note 09 for further details.

Controls only at high or low setpoint - Valve seat is probably in need of adjustment. Click on Service Note 09 for further details.

Intermittent problems - Usually due to loose connections. Check wiring, cables, and harness for loose connections and tighten as required. If problem reoccurs, try swapping control cables with a known good MFC to determine if the problem is the MFC, the system controller, or the harness.

Preventive maintenance: Check MFC zero weekly, Check bottle pressure every 2 weeks, Check MFC operation monthly

Note: Do not try to check or adjust MFC zero if the MFC has been used in the last hour. There is always a residual zero drift after usage that will diminish with time.

Expert Tips: Do not leave unused gas lines under vacuum. Small leaks are always present and if the line is not pressurized air and moisture will contaminate the line. We recommend cycle purging with dry N2 and leaving idle lines under pressure to prevent vacuum based contamination.

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