Electronics International MVP-50T, Installation Instructions Manual

Page: 66 / 95

a) Action: Inspect the EDC Middle Connector and measure the voltage on pin 10 and 28.
D. Symptom: “OVR” is displayed for the digital value for a function.
1. Problem: If a channel on the EDC is over ranged (>2.5 volts between the “+” and “-” inputs), an
“OVR” will be displayed for that function. This can happen on a channel that is used to monitor an
Annunciator, Flap or Trim function . The max input voltage for any temperature or pressure channel is
+5 volts to ground. The maximum differential voltage is 2.5 volts. The VI-221 is used to drop the voltage
when measuring signals that switch from ground to bus voltage.
a) Action: Measure the voltage on the EDC “+” and “-” inputs for the function with the problem.
7.2 Pressure Problem with one Function:
Pressure is measured on the aircraft with a pressure transducer. Power (+5 volts on the Red wire) and ground (Black
wire) is supplied to the transducer and a differential signal (proportional to the pressure) is supplied to the EDC on the
White and Green wires.
A. Symptom: Inaccurate, jumpy or zero reading.
1. Problem: One of the four wires from the Pressure Transducer to the EDC is open.
a) Action:
Measure the voltage on each transducer wires at the Pressure Transducer. The voltage
on each wire is as follows: Red wire = +5 volts, Black wire = 0 volts, Green wire = 1.65 volts and
White wire = 1.65 volts.
Short the Green wire to the White wire and look for a zero pressure reading. If you do not get a
zero reading, you may have an open wire.
Ohm the Black, Green and White wires at the pressure transducer to ground. The Black wire
should be grounded, the Green and White wires should not.
7.3 Temperature Problem on all Channels:
Temperature is measured using a temperature probe with type K thermocouple (TC) wire. When the TC junction in
the tip of the probe is heated, a small signal (approx. 23 micro volts per o F) is produced and monitored by the EDC on
two extension wires. These extension wires must be made of type K TC material.
When measuring temperature with TC material, an ambient reference temperature must be provided. This is done with
a reference diode located on pins 10 and 28 of the EDC Middle Connector. The ambient temperature is added to the
differential temperature measured by the TC junction.
A. Symptom: Inaccurate, jumpy or zero readings on all channels.
1. Problem: The Reference Diode on pin 10 and 28 of the EDC Middle Connector is damaged.
a) Action: Measure the voltage on the Reference Diode. Pin 28 = 0 volts and pin 10 = approx. 0.6
volts.
2. Problem: One of the temperature input channels is in an overvoltage state. This can happen on a
channel that is used to monitor an Annunciator, Flap or Trim function. The max input voltage for any
54