Fuel "Control monitor" or "Signal conditioner"

[Ernie Martin]

Pete, in theory I'm with you. But how many repair facilities have a shaker table to simulate vibration? For that matter, how many subject a repaired item to temperature limits to verify specifications? The issue here is going to be money. If Aero-Mach recognizes that it had an obligation to verify conformance across the spectrum of environmental conditions and fixes the unit without additional cost, I think Ed would be doing well.

Ernie

[edasmus]

I hear what both of you are saying. I do struggle with this stuff all the time when it comes to maintenance bills. In a perfect world I would walk into the shop, tell of the problem, and they would fix it correctly the first time. Unfortunately it does not work that way all the time based on the experience I have had over 18+ years of airplane ownership and 7 years of Skymaster ownership. In the real world it becomes a process of elimination starting with the most likely cause and working from there. Inevitably something else gets broken in the process (which I just experienced with a fuel pump wire while trying to repair a leak in the pitot/static system). What I do look for in people is a good faith effort in trying to resolve the problem. Certainly I expect competence but not perfection. It becomes a balance between overall service and occasional frustrations, a balance between working with my home shop versus the time and expense of flying the plane around to different shops. My shop has been in the airplane business for 40+ years and my mechanic has been there since day one. They have been a Cessna repair station forever and I believe they have seen everything there is to see yet sometimes they still get fooled. I do pay for it, a lot, but looking at the big picture, they get most of it right. I wish I could do all this stuff myself but I can't, not even close. So as difficult as it can be, I have to put my faith and money in other people, encourage them to do their best, be a friend, not a jerk, and hope for the best. If I was truly dissatisfied, I would go somewhere else. As for Aero-Mach, they have been always polite on the phone and seem to be doing all they can to fix my signal conditioner. As for the cost, I will pay their bill knowing it was still less than getting a new one from Cessna and chalk it up as another chunk of money to owning an airplane. When the day comes that I don't want to pay anymore, I won't, and the airplane will be somewhere else. This forum is a great way to hopefully take a piece of that cost and put it back in our wallets (and use it for 100LL instead). It's all good!

[Ernie Martin]

Couldn't agree more. Great way to look at things.

Ernie

[stackj]

Absolutely a great attitude!

[Roger]

I too have had reoccuring problems with my left fuel guage, and noticed something a few weeks ago when working on a fuel leak caused by a dried cork . If I played with the wires that go between the outboard sensor, and the inboard, it caused the fuel guage to spike, and at times work. This even if I isolated (taped down) the connections that went through the tank caps.

I now beleive that I may have a crack in the wire itself. Why else when I move them around while isolating the connections, should I get what amounts to different impendence or continuity .

[Pete Somers]

Roger
You have the resistor type system on your T337D, now this system requires quite a bit of maintenance, the grounding of the tank unit has to be 'spot on' if you have any corrosion under the tank units or the ground strap is not clean this system will not work correctly.
On the resistor type system a open circuit from the gauge to the the tank unit will cause full scale deflection of of the fuel gauge, and a short would cause the opposite effect.

Easy check for volts at the tank unit, also check that the tank unit is grounded and no corrosion on any of the connections.

Regards
Pete

[edasmus]

Update: I spoke with Aero-Mach a few hours ago and they are sending my signal conditioner back and they feel they have it working per spec under all conditions now. They found several things wrong and feel they have the unit repaired. I should have it by Monday so I will keep you all posted as to the results. They did say however if I still have problems, they would not attempt another repair but would only sell me an overhauled unit. Aero-Mach did not charge me any additional amount for the second round of repairs so kudos to them. I hope it works when we get it all back together. Stay tuned!

[edasmus]

The signal conditioner arrived today and I promptly went out to the hanger to hook it up. It PROMPTLY failed. My IA got the same intermittent behavior on the gauges by wiggling the 9 pin plug that is attached to the signal conditioner. Aero-Mach is sending an overhauled unit tomorrow to see if I get the same behavior with that one. This is fun.

[Ernie Martin]

I was kind of unhappy when I gave up on the system and now rely on fueling supervision, visual confirmation and time. After hearing what you're going through -- no longer unhappy.

Ernie

[edasmus]

hahahahaha.....Thanks Ernie, that was funny!

[edasmus]

I received the over-hauled signal conditioner on Friday and plugged it in today (Monday). It has the same erratic behavior as my original one.

[edasmus]

Does anybody know what it means, as far as the fuel gauges are concerned, when turning the master switch on causes the gauges to indicate negative or in other words, below empty. When the gauges work, they work fine. When they don't, they indicate below empty. If you turn the master switch off when the gauges are indicating negative, they rise slightly and indicate empty. When the master switch is turned on and the gauges are not working, they get "sucked" below empty. It is probably a short somewhere. Anybody have any theories?

[Pete Somers]

OK Dave.

1. Was thew plug replaced on the signal conditioner?

2. Inspect the plug on the back of the instrument cluster, that does mean removing the plug and checking it.

3. Has your engineers got the proper test box for this system, if not it will make fault finding almost impossible.

I keep on about having a test box for this system, however you choose to ignore me, you cannot maintain the capacitance system without it. I have kept quiet for a while on this one as I just wanted to see what other owners do, and it does seem to me 'not a lot' perhaps you will listen now.

As regard the test box, Cessna made one years ago to cover all the aircraft with this system, this included all the connectors for the signal conditioners. Bendix did one as well and you could use the Cessna connecters.

Let me know how you get on

Pete

[edasmus]

Pete,

I am printing your response and taking it to my shop. You cannot believe how frustrated I am over this issue. This is one of those times when I am simply trusting the people who supposedly know how to fix airplanes. I am an air traffic controller not an electrical tech or maintenance tech. If these people can't fix it, then I lose! Simple as that.

Ed

[edasmus]

What I can tell you Pete is that Aero-Mach has given me two signal conditioners. My "repaired" one and an "overhauled" one. I have them both and the system behaves the same way with either signal conditioner hooked up. That would lead me to believe that the problem is not with the signal conditioner but somewhere else. Maybe that is a bad assumption. I really have no idea anymore.

Ed