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10) Manually match to the lowest possible reflected power using the AUTOMATCH
panel (see sub-section 2.3.2), and make sure a plasma is running. Adjust the error
signal zero potentiometers RV1 and RV2 (located on the same side of the AMU as
the RF in connector; see Fig 1), while monitoring the two error signals on JP3 pins 1
and 3 (See Fig 6). These should be less than 20 mV when a match exists. Amplified
error signals are accessible at TP 10 and TP 110; these should be made as low as
possible when the RF is well matched.
For Vacuum Capacitor AMU (AMU board REV05 and earlier):
If it is not possible to find a match position due to the match position being beyond
the range of the capacitors, stop the process and remove the AMU cover again. If C1
is attempting to drive above the maximum position, add 180 pF padding capacitor
(Part Number 94-ECC1218), or turn 2 turns anti-clockwise towards maximum. If C1 is
attempting to drive past the minimum position, remove a padding capacitor if
already fitted, otherwise turn 2 turns clockwise towards minimum. If C2 attempts to
drive above the maximum position turn 2 turns anti-clockwise, if C2 attempts to
drive below the minimum position, turn 2 turns clockwise. Whilst doing this, be
careful not to turn the capacitors beyond their physical end stops.
For Vacuum Capacitor AMU (AMU board with capacitor range mod.):
If C1 attempts to drive above maximum position, add 180 pF padding capacitor. If C1
is attempting to drive past the minimum position, remove a padding capacitor if
already fitted. If C2 attempts to drive past maximum or minimum position, check
that the correct inductor is fitted and that the capacitors are correctly fitted to the
system. If these are correct, the match position is out of the range of C2.
For Air Vane Capacitor AMU:
If C1 or C2 attempts to drive above maximum position, add 180 pF padding
capacitor. If C1 or C2 is attempting to drive past the minimum position, remove a
padding capacitor if already fitted. It is not necessary to reset the positions of the Air
Vane Capacitors.
11) Increase the RF power in a few steps to maximum and check for RF leakage, arcing
or local overheating.
12) Rematch manually, when at maximum RF power, manually to less than 1% reflected
power if possible; less than 3% is the maximum reflected power acceptable. Refine
the zero settings of the error signals.
13) Make a note of the capacitor position values when a good match is achieved. Stop
the process and adjust the park positions to a value below that of the match position
(within around 050 units on the position display), making sure that C2 is closer to its
match position than C1.
Re-start the process with the AUTOMATCH panel’s Auto button selected (see sub-
section 2.3.2) to make sure the match is successful. If there is a large reflected power,
repeat Step 10. If there is a small amount of reflected power, which can’t be reduced
manually, RV1 and RV2 on the side of the AMU can be used to make finer
adjustments when in auto mode.
14) If the capacitors oscillate when in auto, reduce the gain of the control circuit by
slowly turning RV1 and RV101 anti-clockwise (if C2 oscillates adjust RV1, if C1
oscillates adjust RV101) until oscillations stop. If the potentiometer’s RV1 or RV101
begin to click before the oscillations have ceased, turn them fully clockwise until
OIPT Automatch Unit
Issue 6: September 05 Page 12 of 20 Printed: 16-Nov-07, 9:26
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