I'm hoping someone on here smarter than I know a little bit about avionics/electronics. Today I went to take a couple of my nieces flying and had an issue with my 340. Once started, everything powered up normally with the avionics master switch. When I went to ask if they could hear me, apparently the volume was loud in one or both their headsets and they screamed loudly into their mics. About half a second into the scream and my audio panel powered down. Dead. I checked for a popped circuit breaker and tried to reset it by powering everything down and back on again. Nothing.

In trying to do some research, the Pilot's guide says that there is a fail safe circuit that leaves the number 1 com active. When I pushed the transmit switch, the T illuminated on the KX-155. I didn't try to broadcast, but this fail safe circuit may very well be its current state.

Doing some more research, I found that the GMA 240 had an issue with an internal fuse blowing. In reading some of the accounts from a thread on the Van's Air Force site, it sounds similar. It's a design flaw in the 240 and, although some asked, it wasn't verified that the 340 has the same flaw. Here is that discussion.

http://www.vansairforce.com/community/archive/index.php?t-93879.html

If this is my issue, it seems like these guys were able to fix the fuse themselves on the 240. Where I don't have a warranty to void (I bought it used), it seems like it's worth a try. The $600+ Garmin wants is nearly what I paid for it. Anyone have any experience with this or avionics expertise?

Thanks,
Cory

Well, we found an inline circuit breaker that we didn't know about that was blown. Hopefully that is it.


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Which raises the question "Why did the circuit breaker trip?" My rule of thumb on that is "One reset only, and if it triggers again, there's an underlying problem that needs to be corrected before flying it again." BWTHDIK?

This isn't 340-specific, but I've been told by computer guru types that just turning a computer of any kind off and back on right away isn't good enough, because some of the pieces and parts tend to hold onto the information/charge or whatever. Almost universally, they say turn it off, count to 10 slowly, then turn it back on. Seems to work most of the time.

Obviously that wasn't your issue, but a blown CB that isn't part of the airplane's power buss may be related. Many CBs that are part of an individual box are really minimal, so some transient voltage that pushes its limit from time to time will eventually cause it to pop--or if it's a fuse, to blow. So I agree that one reset (or one new fuse) is OK, but if it blows again, better find out why.

Cary

JP256 wrote:Which raises the question "Why did the circuit breaker trip?" My rule of thumb on that is "One reset only, and if it triggers again, there's an underlying problem that needs to be corrected before flying it again." BWTHDIK?

The CB didn't trip. An in line fuse, however blew. The why it blew will hopefully be answered when my avionics guy looks at it tomorrow. Stay tuned!


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And agreed on the CB reset count of one. I think that is pretty universal thinking. If it were popping, repeatedly, there is a reason. Keep resetting it and it could very well weld in the close position, leaving no protection.


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