Electronics International MVP-50T - Manual (Page 56)

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A. Symptom: A. Symptom: A. Symptom: A. Symptom: 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 over voltaged. 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. 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 each of the temperature channels.
7.4 7.4 7.4 7.4 7.4 Temperature Problem with one Function: Temperature Problem with one Function: Temperature Problem with one Function: Temperature Problem with one Function: Temperature Problem with one Function:
Temperature is measured on the aircraft 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 ‘F) is produce and
monitored by the EDC on two extension wires. These extension wires must be make 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 tempera-
ture is added to the differential temperature measured by the TC junction.
A. Symptom: A. Symptom: A. Symptom: A. Symptom: A. Symptom: Inaccurate, jumpy or zero reading.
1. Problem: One of the two wires from the Temperature Probe to the EDC is open or shorted to
ground.
a) Action: Remove the extension cable from the probe. Ohm both wires to ground. Each wire
should measure 12.1K ohms to ground.
2. Problem: The temperature probe has a problem.
a) Action: Ohm between the two leads of the temperature probe. You should get a short (<10
ohms)
Ohm one lead of the probe to ground. You should get an open (> 100K ohms).
7.5 7.5 7.5 7.5 7.5 N1 or N2 RPM Problem: N1 or N2 RPM Problem: N1 or N2 RPM Problem: N1 or N2 RPM Problem: N1 or N2 RPM Problem:
An N1 or N2 Tach Generator produces a sine wave at a frequency equal to the RPM of the engine. The
voltage level of the sine wave is very low at low RPM and can be above 20 volts at high RPM. The signal is
generated from a coil inside the unit. Most Tach Generators have three coils and one end of each of the coils is
tied together as a common. On some Tach Generators the common ends of the coils are grounded. The EDC
only need a signal from one coil. In this case, one pin on the Tach Gen should be routed to the RPM input on
the EDC.