Hi, I’m David Crocker, and I run a software consultancy and tools company specialising in critical software. If you’re interested in that topic, visit my work-related blog on formal verification of C/C++ software. I’m creating this additional blog primarily to share my experiences in mending things, or getting things mended, and for anything else that doesn’t fit on my verification blog. With luck the content will help others solve similar problems and avoid unnecessary expense.
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David Crocker's Solutions blog 
I have a 79 t tail lance with a 3c autopilot. It has worked great for 2 years since I bought it. After a hard rain, with now hangar space at an overnight stay, the windshield leaked into the suction filter and took out the DG and the AI. After replacing those…..the autopilot seems to work now, except for alt hold. Do you have any ideas where to start? I’m in South Carolina, FYI, 500hrs VFR working on IFR pilot. Thanks! andy
First check whether pitch hold mode works. Fly the aircraft with the autotrim turned off, adjust the pitch wheel until the pitch indicator is horizontal, then engage pitch mode. Does the autopilot hold the current pitch angle, and respond to adjustments of the pitch wheel by changing and holding the requested pitch angle? If yes, then the fault lies in the altitude capsule or the wiring between it and the console, or just possibly in the console itself. However, if the aircraft is unstable in pitch hold mode (pitching way up or down according to the setting of the pitch wheel, and then not correcting), the fault is lack of feedback from the AI. In this case, suspect the round blue connector on the back of the AI, or the pair of blue connectors near the AI that connect the main loom to the glideslope loom. These will have been disturbed when your AI was removed. When you disengage the latch and separate the socket from the plug or the AI, you should feel a reasonable amount of friction. If they are loose, you can tighten up the sockets temporarily by pushing a needle between the outside of each half of the split socket and the blue surround. If that fixes the problem, it’s probably worth getting the sockets replaced.
Dave , so a mirrored print surface won’t work with you differential IR Sensor.
Thanks wbrokow@gmail.com