SV-EMS-220 errors

[Janekom]

I have a customer with what seems to be a faulty EMS-220 unit. Unfortunately I am not close to the aircraft and relay on what was given to me.
They have SN 2716 installed in an RV9A. It has developed a few problems:

On Master On the some readings jump around and then stabilize.
With the motor running all EGT and CHT readings spike high when the PTT is pressed. I remember something about older units that needed filters?
Then when they advance the throttle the RPM reading will fall away just before max RPM and the MAP starts fluctuating. I think the RPM might be resistor values?

I then gave my spare unit to them to test with. This is SN 7431
All the faults are no more, but the Amp meter is crossed out.

Is there perhaps a pin change for the current shunt that I have missed or do we have two faulty units?
Your expert advise will be welcomed.

 

[jakej]

Ah, the joys of 'remote' troubleshooting.
EGT/CHT 'spiking' are a known issue for some earlier EMS units fixed initially by using filtered dsub connectors & then by a hardware fix.
RPM - is there a 30KoHm resistor added to each p-lead to EMS rpm input - assuming it has mags only ?
Map - is there a restrictor in the tubing to the MAP sensor ?
AMP - maybe a connection issue here or a blown 1 amp fuse ?
First flight or does it have some hours on it ?
If it is a tip up & the EMS is mounted on the Inst panel side of sub panel then the EMS may have had some water in it - evidence of that will be some corrosion in the dsub plugs on the EMS.

 

[airguy]

On the RPM, the 30k-ohm is a suggested starting spot, but some installation have needed more, as much as double that resistance, to get reliable results.

 

[Janekom]

Thank you Jakej and Airguy, yes the joys of remote troubleshooting is fascinating at times. Some of the questions I cannot answer right now. It is an RV9A about seven years old. I think some of the problems were there from day one but ignored.

The main question here is - why would the replacement unit not show Amps?

 

[Janekom]

Airguy I have had to use resistors a high as 120 k-ohm

 

[jakej]

Did it show amps at any stage ? If not then I'd be -
checking the fuses, connections & menu settings etc.

 

[airguy]

The amp measurement is a simple voltage input on two pins to the EMS - one on each side of the shunt. The shunt should be sized to have a voltage differential across it of 1 millivolt for each amp passing through the shunt. 7 amps = 7 millivolts, etc etc. The EMS will look at the voltage differential in millivolts between those two inputs and display it on the Skyview as "Amperage". If it's showing a wild number then you've probably got a wire fault and the values are outside the expected range, or a configuration fault where it's looking for the wrong kind of shunt. If it's showing a big red X over it, I would suspect a wire fault as the same thing happens with a thermocouple or pressure/temperature transducer when one leg becomes disconnected.

Start with the EMS plug - find the pins that are connected to the shunt, and ohm them out to the shunt to confirm connectivity. My bet is a loose connecting screw on the shunt or a broken wire on the EMS DSUB pin. Those wires (28 gauge is sufficient, they only carry a signal voltage) are usually connected to the shunt via a very small fuse or fusible link - 1/2 amp is more than sufficient - so if anything contacted one of the pins or cut through the wire insulation while power was on, you'll blow that fuse and will only have one (or zero) feeds to the EMS on the shunt pins - which the EMS interprets as a sensor fault and displays the red X.

 

[Janekom]

Airguy maybe I am not explaining correctly. The one EMS shows Amps and the replacement EMS no Amps. I am thinking it is an internal fault and was just trying to get confirmation here. The wiring and the shunt is fine.

 

[airguy]

Possible - but much more likely to be a wiring or pin problem. If you've confirmed those are good, then an internal fault becomes more likely and you'll need to discuss with Dynon tech support.