If a T.C. was wired "backwards", what would happen?

tawood

En-Route
Joined
Sep 22, 2015
Messages
2,558
Location
SE Michigan
Display Name

Display name:
Tim
The reason I ask...

I recently bought a yellow tagged turn coordinator, and had it installed the other day to replace my old T&B. I took the plane out for a test flight last night, and the turn coordinator was indicating the turns "backwards", i.e. left turns showed as right, right turns showed as left...I also noted that the power "flag" was indicated whether I cut the power or not. The TC does "spin up" (I can hear it), and if I kill the power to the TC, it stops indicating turns all together.
 
Could be what caused this?
20170102_101122-jpg.55535



But, probably not.
 
I would expect a "wired backwards" TC to not work, even causing circuit protection to do its job.

Simple DC motors run quite happily backwards when wired backwards. A backwards spinning gyro will indicate backwards, so that's likely your problem. If it's something more modern like a brushless motor (dunno what's normally used nowadays) then the electronics may or may not be tolerant of reverse polarity, it may or may not run but I wouldn't expect it to run backwards.
 
Could be what caused this?

But, probably not.

(edit) Excuse me all to hell. The MG suffix on that 78 series regulator is a variable voltage output regulator, which is what that 10K pot to the right of the blown-out chip is for. However, that unit is so far out of production that I can't find but a tattered and scratched up data sheet. HOWEVER, if you would like to kluge in a current production regulator, we could possibly get the thing to work.

The alternative is to try places like "Graveyard Electronics" that keeps stock on old stuff like this, but to be honest, I've never seen that particular package style before with the bat wings for a heat sink. At least not in that particular style. My hit is that those wings at one time came out perpendicular to the chip case and the manufacturer bent tiem down in order to bolt them in.

jw


Yes, reversed polarity will take a 78 series voltage regulator out. The problem is that whatever blew the guts out of that chip took the regulated voltage spec with it. The 78 series of voltage regulators come in a whole bunch of flavors ... 5 volt, 9 volt, 10 volt, 12 volt, 15 volt, and so on. Without knowing the second line of that printing on the top of the case, you will just be wild @$$ guessing at what the manufacturer chose to run their motor with.

My comment in another thread is valid here. A dime's worth of zener diode will (a) help with transient spikes and (b) blow the fuse/breaker with reversed polarity. I guess a dime's worth of protection on a $500 instrument is too much to expect.

JIm
 
Last edited:
If the TC is wired backward you will turn left when you push the yoke right.
 
Back
Top