I have a D120 installed in a RV7-A. The aircraft has not flown although the engine has been run 4 times. Initially the CHT readings appeared to be accurate. I now have a -9 reading on CHT #1. This reading is the same whether the engine is running or not. I have checked the wiring to #1 CHT and have good continuity to the D120. I also swapped the sensor with #3 CHT and the #1 sensor gave a good reading when connected to the #3 Wiring. The #3 sensor connected to the #1 wiring then registered -9. Seems to me the D120 is at fault, can you give me a suggestion to resolving this problem?
CHT Problem
- Thread starter Tricobob
- Start date
- Joined
- Mar 23, 2005
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- 13,226
So I'm not sure we've ever seen a bad CHT channel when we've actually had a unit back. My guess is it's in the harness somewhere, even though you've tested continuity. Double check that the pins at the connector end are actually fully inserted into the DSUB - that has often been the culprit.
One way to test the instrument is to short the +/- inputs of that CHT channel together (ie, run a wire between the positive and negative inputs on the D25 connector. Ideally, you want to do this with your harness disconnected to isolate the harness. If you do this, it should read about ambient, maybe plus a few degrees. If it doesn't, it's either a broken connection between the EMS and where you shorted the wires, or the EMS is bad. Again, I don't think we've ever seen an EMS with only one channel bad.
One way to test the instrument is to short the +/- inputs of that CHT channel together (ie, run a wire between the positive and negative inputs on the D25 connector. Ideally, you want to do this with your harness disconnected to isolate the harness. If you do this, it should read about ambient, maybe plus a few degrees. If it doesn't, it's either a broken connection between the EMS and where you shorted the wires, or the EMS is bad. Again, I don't think we've ever seen an EMS with only one channel bad.
jakej
Well-Known Member
Did you check to see if any of the wires are 'retracted' at the Dynon connector end ?
Although they may appear to be ok refitting the connector can cause issues especially IF you bend the harness in any way while doing so - hold the connector in one hand and wriggle the harness with the other, you'll see what I mean.
FWIW I've never had cause to ship a unit back to Dynon due the symptoms you have but I did some head scratching until I worked it out.
From my experience (have done many installs of dynon equipment) the issue is due to the inherent stiffness of the thermocouple wires and how the backshell is fitted. the wires at the outermost ends of the connector are usually at fault but some of the others can come into play as well.
What seems to happen is the wires are 'pinched' together when the assembly is done causing a lot of strain on the pin sockets in the connector sometimes resulting in damage. Moving the harnes as mentioned will demonstrate what I mean, the pins will move in/out like pistons.
There is a fix for this situation, which is better done before installing the harness. What I do is remove the backshell & heatshrink, carefully bend the outermost wires towards the centre of connector & reassemble - problem goes away
HTH
Jake J
Your procedure sounds good to me and I think is worth doing. However, I have in effect bench tested my unit and bypassed the harness. I consistently get a -9 reading on the #1 CHT both shorting out the pins on the back of the D120 and by directly connecting the #1 and #3 probes to the unit not using the harness. BTW, one other thing is that my D120 makes a ticking noise when hooked up to power. I do not know if this is normal or not.
- Joined
- Mar 23, 2005
- Messages
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The ticking noise is normal.
jakej
Well-Known Member
"I consistently get a -9 reading on the #1 CHT both shorting out the pins on the back of the D120"
Not sure that I saw that comment earlier - however that has narrowed it down. 'ticking' noise is normal
Hopefully my comments, Reply #4, will help others troubleshoot their issues too.
Jake J
Not sure that I saw that comment earlier
- however that has narrowed it down. 'ticking' noise is normal Hopefully my comments, Reply #4, will help others troubleshoot their issues too.
Jake J
Just to let you know the end result of this problem. After considerable pain and suffering, it turns out the problem was that GP #3 was set "Rotax L" when it should be set to "unused". I do not think this fact is in the documentation but changing the setting on GP #3 instantly fixed the problem.
jakej
Well-Known Member
Tricobob
Wow, that was unexpected as I (we) thought you would have the settings done correctly.
Glad to hear all is well now , enjoy
ps - thnkx for the feedback.
Jake J
Wow, that was unexpected as I (we) thought you would have the settings done correctly.
Glad to hear all is well now , enjoy
ps - thnkx for the feedback.
Jake J