KFC 150 self test, trim failure

[slowflyin]

My autopilot worked great on the previous flight but failed the self test this morning.

 

Power up

Trim illuminates

Test Botton Depressed

Four Blinks 

     KS179 hums with each blink but sprocket does not move.   Seems like this is the issue.  

Five Beeps

Continuous Beeping.  

AP disconnect stops beeps while depress but they return when released.

 

 I've cleaned the pitch servo connection, trim servo connection, and re-racked the AP.  

 

thanks in advance,

joe

 

[redbaron1982]

Is the electric trim working if you use the trim switches in the yoke?

[slowflyin]

No Sir

[redbaron1982]

Did you check your fuses? Are they all in? Anyone popped?

[Rick Junkin]

@slowflyin I have a KS 179 servo as removed from my Bravo when I got my GFC 500 installed. PM me if you determine you need one and this part number works for you 065-0052-14.

Cheers,
Junkman

[slowflyin]

25 minutes ago, redbaron1982 said:

Did you check your fuses? Are they all in? Anyone popped?

All good

[natdm]

There's been a few threads about this on here, I think. I have the 200 so not quite the same. We had to replace the AP disconnect button and while we were removing the switch, we saw that the wires were never correctly soldered on, so they would lose connection and that's what would turn it off from time to time. 

[natdm]

@slowflyin for kicks.. maybe do what I did to test. Click the disconnect button a zillion times and see if it automatically starts to work again. I think my mechanic and I had to click it like 20 times and then it re-connected. That's how we decided it was the disconnect.

[PT20J]

When this happened to mine, it was intermittent and turned out to be a bad connection between board in the computer. Probably @Jake@BevanAviation will have some things for you to try to isolate it.

[slowflyin]

55 minutes ago, natdm said:

@slowflyin for kicks.. maybe do what I did to test. Click the disconnect button a zillion times and see if it automatically starts to work again. I think my mechanic and I had to click it like 20 times and then it re-connected. That's how we decided it was the disconnect.

I checked continuity with a meter and it shows NC at rest and open with a click.  I'll be checking the CWS and trim switch in the morning.  Thanks for the post!

[wombat]

The trim motor humming but not moving is very indicative of a trim motor failure.   You might give the folks at https://www.autopilotscentral.com/ a call.  They IRAN'd mine and it works perfectly.    

 

Apparently there are a couple of other common problems that might be very inexpensive to troubleshoot or solve.

1. The three microswitches in the 'trim up' and 'trim down' switches on the yoke can fail and either the normally closed parts are open, or the normally open parts are closed.  But you can just take a multimeter and figure that out.
2. The normally closed switches in the "AP Disconnect" switch in the yoke can fail and be open.  This is also pretty easy to measure with a multimeter.

[slowflyin]

Just now, wombat said:

The trim motor humming but not moving is very indicative of a trim motor failure.   You might give the folks at https://www.autopilotscentral.com/ a call.  They IRAN'd mine and it works perfectly.    

 

Apparently there are a couple of other common problems that might be very inexpensive to troubleshoot or solve.

1. The three microswitches in the 'trim up' and 'trim down' switches on the yoke can fail and either the normally closed parts are open, or the normally open parts are closed.  But you can just take a multimeter and figure that out.
2. The normally closed switches in the "AP Disconnect" switch in the yoke can fail and be open.  This is also pretty easy to measure with a multimeter.

Thanks!  I'll check the Trim switch and CWS in the morning.  If all is good I'll follow up with a call the AP Central.  

[Jake@BevanAviation]

During the A/P test, the 4 flashes of trim is two up pulses and two down pulses to the trim servo.  The computer sends this drive and looks for feedback to see if the motor ran or not.  You never see the motor turn the capstan cause the solenoid does not engage during this test. However, if you listen for the trim servo to run in the tail you should hear it run 4 times then stop. If MET (manual electric trim) is not working I would check the regulated trim voltage (pin A of trim servo connector).  This has to be within a certain tolerance as the autopilot (KC19X) monitors this voltage.  If this regulated trim voltage is not within a certain tolerance or missing the unit will fail PFT.

[slowflyin]

1 minute ago, Jake@BevanAviation said:

During the A/P test, the 4 flashes of trim is two up pulses and two down pulses to the trim servo.  The computer sends this drive and looks for feedback to see if the motor ran or not.  You never see the motor turn the capstan cause the solenoid does not engage during this test. However, if you listen for the trim servo to run in the tail you should hear it run 4 times then stop. If MET (manual electric trim) is not working I would check the regulated trim voltage (pin A of trim servo connector).  This has to be within a certain tolerance as the autopilot (KC19X) monitors this voltage.  If this regulated trim voltage is not within a certain tolerance or missing the unit will fail PFT.

Thanks Jake!   Yes, when in test mode I placed my hand on the trim servo and could feel four distinct hums.   MET is not working.   I'll check Pin A.  Thanks again!

[slowflyin]

8 minutes ago, slowflyin said:

Thanks Jake!   Yes, when in test mode I placed my hand on the trim servo and could feel four distinct hums.   MET is not working.   I'll check Pin A.  Thanks again!

1.6 volts continuous 

[Jake@BevanAviation]

What is the long part number of the trim servo and I can tell you what the regulated voltage should be.

Edited June 24, 2024 by Jake@BevanAviation

[slowflyin]

1 minute ago, Jake@BevanAviation said:

What is the long part number of the trim servo and I can tell you what the regulated voltage should be.

PN 065-0052-14  SN 4191   

[Jake@BevanAviation]

28VDC input power, 25-27VDC regulation on pin A.  If you monitor pin A with the servo connector plugged into the ship you should have 25-27VDC.  Anything outside that spec would cause a PFT failure and if the voltage was too low MET would not be functional.

Edited June 24, 2024 by Jake@BevanAviation

[slowflyin]

 I measured with it plugged into the ship.  I'll double check in the morning.  Thanks again Jake!

[hazek]

On 6/24/2024 at 10:52 PM, Jake@BevanAviation said:

28VDC input power, 25-27VDC regulation on pin A.  If you monitor pin A with the servo connector plugged into the ship you should have 25-27VDC.  Anything outside that spec would cause a PFT failure and if the voltage was too low MET would not be functional.

Could too low RPM when idling parked then cause the AP test to fail? Am I understanding this correctly?

[slowflyin]

Mine read something like .8 volts with 28 volts on the buss.   Servo is off for IRAN.

[Fly Boomer]

On 6/24/2024 at 3:52 PM, Jake@BevanAviation said:

28VDC input power, 25-27VDC regulation on pin A

Do you use some sort of break-out box to gain access to the pins?

[Jake@BevanAviation]

You can back pin the connector if you take the back shell off or use a test box which we have.