Inbound write-up of the #2 A/P disconnecting. CFDS flight fault review showed roll system failures. A return-to-service test on just the aileron had no yoke movement.
Removed the #2 FCC and shot all associated coils of the right-hand inboard aileron actuator. The actuator has one MOD LVDT(4 coils to be shot), one RAM LVDT(four coils), one SHUTOFF VALVE (two coils, but only one reading), and one FLOW CONTROL VALVE (two coils, one reading).
All coil values are called out in the Fault Isolation Manual. One point to be made is the excitation coils for the two LVDT's which are in parallel. The FIM asks for pins to be removed from a terminal block in the E&E to isolate them. That is NOT needed. There are two plugs on the actuator. P1 has the RAM LVDT wired through it. P2 has the MOD LVDT. Pop one plug off do a reading, put that on and pop the other plug off for the second LVDT coil to be read.
For this problem, the SHUTOFF VALVE coil was reading high. When P2 was removed it had pretty bad moisture. It could of been water, de-ice, or hydraulic..... either way, a cleaning and re-seat did the trick. The actuator engaged and operated correctly.
As a note, all components except the RAM LVDT are replaceable. P2 is located by the FLOW CONTROL VALVE. P1 at the rear of the actuator.
Pitch and Yaw actuators are basically the same and they can be troubleshot in a similar fashion.
Proper shutoff valve reading.
MOD LVDT pins A&B excitation coil: pins P&R of P2 on actuator which are easier to shoot from E&E.
MD-10-10 ATA 22-12 Auto-Pilot Roll
Schematic Manual 27-33-3
Fault Isolation Manual 22-12
Sometimes, just taking the plugs off and putting them back on will clean a dirty pin that is causing an issue with an actuator.
If I have them off, I usually douse them with alcohol. Both plug and receptacle.
I DO NOT USE CONTACT CLEANER. I do not use Deoxit
Contact cleaner comes out freezing cold. In our jungle environment down here, the pins immediately get condensation on them. If the plug is placed back on before that water has evaporated, you now have "more" possibilities for corrosion.
After I do an alcohol spray, I shake things out and give everything a chance to dry before reconnection.
The purists might say I'm leaving a film on the pins. I doubt that and I'm damn sure that they are a lot cleaner than what they were covered with before, dirt, de-ice fluid, and/or Skydrol.
I don't dislike it. I would rather just grab some alcohol for cleaning.
Plus...... I don't know the half of all the chemicals being absorbed into my skin. Synthetic engine oil, Skydrol, 1422B-1/2 (no matter how much I try to not get it on me), Toluene, LPS, glass cleaners, and fuel to name a few. Deoxit is just another chemical compound that I get on my skin whenever I use it.
My liver is already shot. No need to add any more strange stuff to it. At least with alcohol...... I know what I'm getting and I've had plenty of experience with it. That "would" include the drinking kind also.