Sandel SN-3308 Headache

[azure]

I took my Sandel to the avionics shop today to have its lamp replaced, as although by hours it is only halfway through its recommended life, Sandel does recommend replacing the lamp every year and it has been over a year since mine was last changed. The lamp change set me back about $250, but seemed to be routine. Then: after setting a course on the GPS (a 480) back to home base and taking off, I noticed the Sandel CDI needle quivering and then snapping to center, very abnormal. To test whether it was indeed malfunctioning, I flew away from my course at a right angle. Same behavior. The 480's NAV page showed that the GPS's deviation information was reasonable, and its HSI-like display showed correct deviations. Only the Sandel was malfunctioning.

I later determined that the left/right deviation indications are also faulty in VOR mode, and the to/from flag was missing from the display. These items also fail to test properly upon powering up the avionics. The GPS tests the functions but is completely unaware that the Sandel is not displaying any of the commanded functions (CDI centered, full & half left/right, VDI centered, full & half up/down, to/from flags on and off, all these commands are shown as tested on the GPS, but have no effect now on the Sandel -- very different from when I took off from home this morning).

The Sandel installation guide shows that all of the affected functions involve inputs carried on adjacent pins of connector P1 (the last 1/4 of the length of the connector on the opposite end from pin 1). So I'm thinking, hopefully, that it might just be a seating problem with the Sandel. Just wondering if anyone else has had a similar experience, and what the problem ultimately turned out to be.

 

[LDJones]

I'm guessing you are guessing right. Either something got bumped while replacing the bulb or something wasn't reconnected properly.

 

[denverpilot]

Anytime maintenance is done on any electronics and then it misbehaves immediately, it's usually physical connection or cable related. I'd do some reaching and wiggling.

 

[azure]

Anytime maintenance is done on any electronics and then it misbehaves immediately, it's usually physical connection or cable related. I'd do some reaching and wiggling.

I tried pressing on the bezel to no avail. Since it is several adjacent pins, I'm thinking possibly bent pins and don't want to risk doing permanent damage by messing with it myself and am going to leave it to the expert. My avionics tech is waiting for me at 1000 today. Just a PITA to have to waste another day and more avgas to correct a problem he should have detected immediately.

I didn't mention this before, but I had a seating problem with the 480 too that his assistant tried to fix AND FAILED. That manifested as an "unable to command transponder" alert from the GPS on startup. He redid the job and so far, no recurrence. But it sounds like a bad day at the office over there. Very unusual, this is a top rated shop that I'd normally trust with any avionics issue.

 

[azure]

I'm guessing you are guessing right. Either something got bumped while replacing the bulb or something wasn't reconnected properly.

Yep, it was indeed a connection problem. Actually a problem with the panel plate itself that did not properly accommodate the shape of the unit. When the screws were tightened, it pulled the unit out of the rack slightly. The shop modified the plate, problem fixed.

Would that the other problem was as simple to fix. Frequent "unable to command transponder" message on the 480 on startup. It controls a remote SL-70. The problem seems to be impossible to reproduce without starting the engine. The shop re-racked both the 480 and the SL-70, checked the RS-232 connectors on both ends, and carefully checked continuity. Everything checks out, but the problem persists. Bill (avionics guru) suspects there is a connector somewhere between the panel and the tailcone that is bad, but it would be a beeyatch to pull all the wiring to find it. Sometimes I hate airplanes.

Fortunately I have a panel-mounted SL-70 as backup.