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Discussion in 'Shiny Things' started by Weirdo, Dec 23, 2004.
Check the service loops.
If you haven't solved it yet, you might want to give a description of the problem. Lot of EE's here as well as others with experience who may be able to at least point in the right direction.
I can pm it. Didn't want to clutter the thread with our own saga
Oh, come on... it ain't all about purty pitchers, you know
mate, there are pics of an ericson skycrane on the last page, i shall put some Mil8 pics up later - Hedge is right, its not all about pretty pics!
Spill the beans!
Hay Ewe and Bear
I'm not an A&P an EE, or an ET, I'm barely a pilot, just a working guy who wants to get back work riding shotgun looking out the window and pushing buttons on a computer.
11000 hour airframe, hot section inspected and brought up to snuff 60 hours ago.
One morning pilot hits the starter and N1 gauge doesn't move off 0%. Can hear it turning. Check with reputable mechanic he says 9 out of 10 times its the tach generator. We order both the gauge and the generator to cover our bases, we've got work to do...
Mechanic installs parts N1 is functional.
Off to work fly to job.
Fire up aux electronics for work
Generator circuit breaker pops (10 amp on the panel).
Shutdown aux. equipment and reset breaker we had just powered up this equipment and it pulls quite a bit of power so we thought maybe it had caused the breaker pop.
Pops again within minutes with our aux. equipment off.
Shutdown non-essential electrics go to battery, leave the Gen switch on with circuit breaker pulled as per POH instruction for engine out horn.
After the second breaker pop we noticed the TOT is twitching erratically 150-200 degree sweeps both up and down seems in error as the machine is performing fine and N1 and N2 are showing no problems.
Return to base
Since that day:
TOT RELATED items addressed
New engine harness for TOT was installed 60 hours ago
New plug-in wiring from cannon plug on gauge to where it terminates.
Guage and wiring have been tested with appropriate testing equipment. Whatever it was tested with had just been sent in for calibration so we’re pretty confident that all these items are functional
TOT worked for a few starts and stayed solid for 10 minutes or so each start so we thought at least the TOT was under control
Starter Generator Related
The main issue is still Generator circuit breaker
Generator was sent out and tested and checked out good still has 700 hours until rebuild but we wanted to rule it out
10amp circuit breaker replaced
Generator switch replaced
New GCU installed and adjusted to factory setting (29v?)
Aft line connector/relay replaced
One chafe was found on the generator switch wiring and sealed up
After the line connector was replaced Gen breaker still pops our TOT started twitching again and the engine out horn started sounding intermittently even near 100% N2 previously it only sounded when we would preflight and run the governor check it would sound at 95%.
EPO (Engine Power Out) box tested by manufacturer and sent back clean bill of health
So maybe we've got two problems or we've got one problem that is wreaking havoc on multiple systems.
Could be in the harness, could be some out of the box thinking and a component that seems unrelated is causing us a lot of grief. I know I've got nothing to add, but I have a lot of confidence in the Advrider community and the surprising depth of knowledge I find here.
We parked next to (next to being a relative term) one of those orange S64's a few weeks ago.
It sounds like you have a short or miss-wire someplace. Given you just swapped a harness, I'd have to guess it's either on a connector (maybe miss labeled/miss wired) or there is more damage to the harness that a simple chafe.
Well, there's your problem
Have you guys made any recent additions to your avionics?
I've thought this the entire time, tomorrow we try a suggestion from MD. If that doesn't work a lot of wires will start to get replaced.
Not in the last 60 hours.
It's gotta be chafing or cross-talk, then. Double-check that no wire bundles have been routed contrary to the factory route (around hangers and posts, et cetera).
running with my original post.
And quoting hedge..
maybe even a pinch on install.
You said that you want to get flying and push computer buttons
You said that your equipment pulls quite a bit of power
You said that the aircraft is old 11,000hrs
You said no changes in the last 60hrs
My suggestion is that your special computer stuff on baord is causing EMF interference. it hasn't been a problem in the past but wireing etc has gradually decayed over the years, the sheilding that was there is no longer able to protect the systems.
You said no avionics changes in the last 60hrs - but when you did, what was the change? what is the new ELA (Electrical Load Analysis) again, might have been ok but as the newly installed equipment has aged, it is ut putting more noise causing this problem.
My Disclaimer is that I only know what a MD500 looks like, and I have no idea what the engine is (Googled it - is it a RR250-C30R series you have installed?) (I think that the C30R is FADEC?) but the EMF your kit is producing is causing a spike some where and causing your problems.
Try making sure that your special install kit is COMPLETLY removed from the onboard power systems and start up and fly and see what happens.
(Insert pop corn image thing here)
The problems exist with the equipment disconnected. I do understand your suggestion but we haven't turned on any auxiliary equipment since the initial breaker pop.
My basic troubleshooting method (can't speak for others involved) is as follows:
When did it work last?
What changed since then?
Could the changes be related?
What systems are effected?
Do the failing systems have any commonalities, junctions, shared components ?
Where are the likely failure points?
Do/can those items create these symptoms?
Test, isolate, recreate the fault, rinse, repeat.
Unfortunately I'm not knowledgeable enough to know the failure points so I'm sharing the symptoms. Thanks again for the help.
thanks for quick reply
what about any other component changes in the last few hours? maybe back the last 60
then as Hedge(?) suggested, check all the wiring
We'll check the log books and see what we can think up.
Out of curiosity, where did the 'new' harness come from? Was it recovered from another A/C? Is it possible it does not match the existing revision levels?
I may have confused some folks, the A/C harness is original only the TOT portion at the engine that looks like a metal squid and a small section behind the instrument panel that runs to the TOT gauge (power for the digital readout below the needle?). The harness is the biggest unknown.
And none of you have mentioned the tendency of strong metal bits to break like glass in that temp range. I was in Dead Horse in the mid '70s and thought the sight of heavy machinery parts shattered by a small lurch or bump was totally fascinating...