Fuel "Control monitor" or "Signal conditioner"

[Pete Somers]

Ernie and Ed

Give somebody like Yingling a call and see if they would hire out a box, all of the Cessna twin engine airplane have this system so they must be around so that you can calibrate the system correctly. Surely you maintenance guys will have some contacts. Give Cessna a call and see if the box they made is still on the go.
I am very surprised that these airplanes are certified without fuel gauges and maintenance shops that have not got the proper equipment to fix a problem?

Regards
Pete

[edasmus]

Pete and Ernie,

I just returned from my shop with your email (Pete's) and amazingly my shop has your magic box. My mechanic says he has rarely had to use it as he was always able to solve these problems by repairing connections. He did say the test box is required equipment to have at a "Cessna Certified Repair Station" which my shop is. As I headed over to the shop, I was prepared to "pull the plug" on this enjoyable little project and live with intermittent fuel gauges but since they have the test box, I decided to let the saga continue. They should have the plane back in their shop by this afternoon (Chicago time) so stay tuned!

Ed

[edasmus]

Well, the problem is still not solved but I guess it is as good as it is gonna be. The good news is that the fuel gauges work about 98% of the time and are stable while they are working. We just cannot seem to completely eliminate the problem. My mechanic saw nothing unusual while utilizing the test box other than he could impact voltage readings simply by by puting his hands around wires. I have no explanation for that. This was not an attempt to wiggle wires to search for a loose connection (although we have done that plenty) but an attempt to simply see what happens if you put your hands around wires.

My original signal conditioner has been sent back to Aero-Mach for good because my shop was able to get that one to consistently fail with the associated behavior of the gauges. They were unable to get the overhauled conditioner to fail but I knew I did when I intitially installed it myself. During the install testing with the test box the overhauled box behaved perfectly but shortly into my first flight (before I left the ground) the problem reappeared. We may be chasing multiple problems here. Who knows......

So my plan is to just fly until the annual in August and see if I can make any correlations with the supposedly random brief failures. My shop is going to work more on the connections at the gauges but as I said, not until August. The airplane is back together now and is going to stay that way and is working well otherwise. If any major developments should occur, I will certainly pass it on. If anyone else out there solves this problem, please share!

[Pete Somers]

Ed
This sounds a good one! I wonder if you have a bonding problem with the tank units. The wires from the tank units to the conditioner are screened and that should not happen. If you squeezed the wire you will alter the capacitance. I think now you need to check the whole bonding of the tank units and the wing joints.
However that is as you say a job at the annual when the panels are off, have the pleasure of flying it for the summer, enjoy!

Pete

[edasmus]

Hmmmm....thanks Pete, I will share that thought with my mechanic!

Ed

[edasmus]

Just got an interesting phone call from Aero-Mach Labs. They told me after receiving my original signal conditioner back at their shop for the third time (after I decided to keep the "overhauled" unit), they bench tested it again and found 5 more failed transistors. This really makes me wonder if the "overhauled" unit I now have is any better than the original one. They did say that under warranty for one year they would be happy to give my overhauled unit that I now have a free "check-up" to see how it is doing. I think I will do that in August/September 2009 when the airplane goes in for annual.

[Pete Somers]

Ed
That is rather annoying, as these people have had the box twice or is it three times and found faults that during the first test should have been cleared. You know it is much like the UK now to get a unit repaired like yours is almost impossible, to get a radio repaired in the UK is the same. The skilled people are just not here any more.
The Skymaster is a easy airplane to both service and troubleshoot all you have to do is go back a few years and think logically.

Regards
Pete

[kragby]

[quote=edasmus;13898]Just got an interesting phone call from Aero-Mach

Anyone have a schematic for the fuel monitor box? That would be helpful. Aero Mach repaired mine but it still didn't work - mechanic here too busy so I did some troubleshooting and found the shielded cable to the outer probe was shorted. After replacing the box would work after warming up for 15 minutes. Just a month out of warranty Aero Mach wants another 800 to repair again. I'd like to trouble shoot the unit myself but need a schematic. Greatly appreciate any help and happy to pay for copy.

[chrisktx]

Went through three boxes with Aero-Mach. Had another mechanic familiar with Pennycap system tell me the connectors at the box are very sensitive. Don’t manhandle and push the leads in too hard. Ok course the left tank is starting to act up after warranty. Gauge wants to read full. After shutdown and restart with partial tanks it registers somewhat correctly. Horrible system.

[edasmus]

Ugh, it is a horrible system. I feel bad you had to go through all that. I would say the fuel control monitor (signal conditioner) and the over-voltage issues I have had, have been the worst issues I have had to deal with over years. Thankfully (knocking vigorously on wood), my fuel gauges have done quite well once I got through that issue. The Skymaster is a great airplane but anything malfunctioning that is electrical is always no fun. Hopefully you are good to go for awhile now!

Good Luck,

Ed