The International Cessna 170 Association

Does anyone know if the piano electrical switches on the "A" model have circuit protection built in? Here is why I ask. I recently replaced my turn and bank with a newly overhauled unit from an instrument repair shop. They said they couldn't get parts for my old one. At about hour number 3 after installation, I turned the turn and bank switch on and noticed an unusually high amperage draw for a couple seconds then a click was heard from under the panel somewhere and the ampere reading fell back to normal. I turned everything off and began trouble-shooting. After a few minutes I heard another click from under the panel. I tried the turn and bank switch again and the same thing happened. No other fuse or circuit breaker popped. The replacement instrument has been sent back to the shop for analysis and warranty repair. By the way, with the turn and bank unit out of the circuit, there is no difference in draw when the turn and bank switch is turned on, and of course no click heard. I measured the resistance of the faulty unit before I sent it back. It showed zero.
Any ideas what the click is coming from?

Stephen,
I think what you hear is the auto-reset CA-2 Klixon circuit breaker found in fig. 58-2 of the 170A IPC.

The Turn and Bank connects to PN: CA-2, which is a re-setting circuit breaker soldered to the buss-bar. The T&B in early days was the PRIMARY instrument for instrument-flight and considered so important that it was delegated it's own self-re-setting breaker. (Your old T&B might not have been bad.)

It sounds as if CA-2 has failed...or you have a short in the T&B circuit.

The placement of this c/b is more clear in the 170B IPC as shown below. Mine wasn't soldered to the buss bar; it has two posts for ring terminal attachment. It looks like, if one knew what he was doing and had the appropriate equipment, the amperage at which the c/b opens could be adjusted with the center set screw.

OK thanks. I will look for it the next time I am at the hangar.

Since my last post on this, I have received the repaired instrument back after warranty repair. It is installed and though I haven't had a chance to fly it since reinstallation, I have powered it up with all the other electrical gadgets on and everything seems to be working fine. The repair shop said there was a bad rotor in it. It was replaced of course so hopefully that fixes the problem.

Thanks again for the info on this!