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Troubleshooting
6.1
Troubleshooting
LED 1
Normal
pulsing
Alarm
pulsing
Probe reversed
on
polarity
Probe wiring
off
open circuit
Probe wiring
off
short circuit
Relay defective
pulsing
Notes:
• Voltage levels are DC, nominal values, and may appear to be pulsing, coincidental with
LED 1.
• If diagnosis does not solve the malfunction, the probe, pre-amp or MFA 4p may be
defective.
• If no spare circuit boards or probes are available for interchanging, the MFA 4p may be
tested as follows in order to determine which section is defective:
– To find out if the MFA 4p is defective:
– To find out if the RMA is defective:
21
LED 2
on
off
off
off
off
on
i. Disconnect the pre-amp.
ii. Set ppm switch SW2 to X 1 position and turn potentiometer to 15.
iii. Connect one Iead of a 530 ohm, 1 watt resistor to terminal 7 and then momentarily
contact terminal 8 at a rate of once per second. If the MFA 4p is functional, the relays
will energize after two puIses and de-energize approximately 8 seconds after last pulse.
i. Disconnect pre-amp from the MFA 4p. Attach probe across terminals TB1 1/2 and a
24 V DC (floating) power supply across terminals TB2 3/2, according to the MSP-3 or
MSP-9 Probe with RMA (remote mounted amplifier) (Page 12) connection diagram.
ii. Run equipment to be monitored at normal operating speed or pass a ferrous object
in front of and as close to probe as possible at a continuous rate.
iii. With an oscilloscope, look for approximately 6 V peak to peak pulses or alternating
hi/lo levels across ground and link 3. Or with an amp meter connected in series
Term 7/8
C8
(note 1)
24 V
27 V
24 V
27 V
20 V
27 V
27 V
27 V
0 V
27 V
24 V
27 V
Operating Instructions, 12/2020, A5E33988839-AC
Term 1/2
Term 4/5
relay 1 out
relay 2 out
closed
closed
open
open
open
open
open
open
open
open
open
open
Milltronics MFA 4p
6
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