J.P. Instruments EDM 760 Instrument Installation Manual - Manual (Page 9)

Installation manual for the EDM-760 Twin STC SA00729SE
Report No. 760
Temperature indicating system with Fuel Flow Date 7/20/99 Rev NC
Page 9 of 19
28) TROUBLE SHOOTING
A missing column in the display upon start up indicates the continuity check diagnostic routine has found an open line or
probe with no connection. An error message will indicate which cylinder to look at.
A missing column in the display during flight indicates a reading that is jumping around or incorrect. The probe is
removed from the line up to prevent false alarms.
A negative reading (-) in front of the number indicates reverse polarity on the red/yellow wire to probe.
Using an Ohm meter or continuity checker measure across the probe output leads. A good probe should be around 2-
ohms and at the connector to the probe around 20 ohms.
Having problems with one cylinder reading ? Swap the suspected probe with a probe from a good cylinder. If the
problem goes to the good cylinder the probe should be replaced. If the problem remains the same, it is in the Thermocouple
hook-up wiring from the probe to the instrument or it can be in the ring terminals crimped to the wire. Remember to double
back on the wire going into the ring terminal.
Display jumps when transmitting on the radio. Review fig-6, a kit is available to stop transmission noise it connects on
pin 11 connector P-1, (mike key button).
EGT, large span. Normally aspirated (carburetor) engines at normal cruise display a “DIFF” of 125 to 175
o F spread
between cyls. Injected engines at normal cruise display a “DIFF” 50 to 90 o F spread between cylinders. All cylinders are
measured by a common circuitry. It is impossible not to have identical calibration on all channels.
If the temperature is changing more than 500 F in one second it should not be trusted and a lose wire crimp or probe should
be suspected.
All EGT or CHT readings seem to High or Low or Unsteady. Use a DVM (digital voltmeter) to measure the difference
between 760 SCANNER ground and the engine block ground. If the difference is greater than 0.5 volts with the alternator
charging. Then remove the EDM-760 ground (Black wire) from the instrument panel and connect it directly to the ENGINE
BLOCK for GROUND.
OAT readings off by 25 degrees, but oil and CHT readings OK, look for copper wire spliced in line to OAT probe. OAT
reading can be fine tuned +/- 5 degrees, see reset procedure. Engine heat could also be the cause.
Gem conversion, CHT’s read high (100 degrees) EDM-760 not calibrated for Gem installation “J” calibration, return to
factory.
Copper Wire can not be substituted for thermocouple wire at any point.
Unreliable Fuel Flow readings high will display as dashes, low will display zero.
START UP ERROR LIST and PROBE LOCATION
Display indicates "OPEN PRB" then the following message on the engine side of the display:
EGT 1 CHT 1 OIL
EGT 2 CHT 2 OAT
EGT 3 CHT 3 TIT 1
EGT 4 CHT 4 TIT 2
EGT 5 CHT 5
EGT 6 CHT 6