Jake@BevanAviation

Originally the 1k 5% 1w load resistors are only used on the Century 4, 41, and 2000 systems. See note below. Service Bulletin 23096 has revised this note and added the Century 21. The latest version of the GI275 IM has this revision included. If you can measure the heading error voltage when the system stop responding, move the heading bug and see if you still see a voltage change. The heading bug error voltage should go above and below the reference voltage. Reference voltage should be around 4.8VDC (half of regulated DC supply 9.6). If the heading error will still change with input the problem is not with the GI275. With Century Flight Systems being out of business support for any legacy system is going to be very limited. As parts continue to diminish there will be even less support in the future. The Century 21, 31, and 41 used a FET gate IC that was used to route error signals on the motherboards. If the gate fails the signal stops at that component. They also used ribbon cables to interconnect the motherboard assemblies. The ribbon cables will delaminate over time and can cause issues as well.

Yes, you would want to use the bracket that is in your aircraft for servo mounting. Just be sure that the servo dash number matches the one you have. Some servos are voltage specific 14 or 28.

Possible issue in the KC191 flight computer or roll servo. If you can gain access to the roll servo and disconnect it from the ship you could monitor to drive command across pins D and L at the roll servo connector to the ship. With a DC volt meter the AI spooled/level, the heading/course pointer under the lubber line, and the autopilot engaged in heading and AP engage modes you should see close to 0vdc. Moving the heading bug left and right of the lubber line should create a increasing DC drive voltage. Going one direction will be positive voltage and the other direction would be negative voltage. This will check the drive voltage from the computer. If you check Pins E to C this is the solenoid engage voltage. It will go positive and stay positive when the flight computer is engaged. It would also be helpful if you could find out what servo version you have. Some Mooney's have the KS-17X series of servos, other have the more common KS-27X series. Both servo assemblies function exactly the same but the KS-17X have different parts and some a getting hard to find.

The autopilot configuration page should be set for KI525 and at default values, the flight director page should be set for KI256 and at default values. The GAD43 gyro emulation type should be KI256. You need to align the flight computer to the GAD using the GAD output test. You should follow King installation bulletin 430 using the King flight line test set (KTS 150). If the KTS150 is not available you can fabricate a breakout harness. The GI275 IM shows how to make this harness if needed.

We had this happen before. Turned out to be the GSU25 had a issue.

I would check the output of the transducer inside the flight computer if the aircraft was here. You can remove the static line to the flight computer and attach a hose to the unit. When applying pressure or vacuum to the hose the computer should respond in the opposite direction. For example with a level attitude source or the ADI unplugged. If you applied pressure to the static line the computer should want to climb to get back to target altitude. If you create a vacuum the system should want to descend to get back to target altitude. You can do this with your mouth as the system is very sensitive to pressure changes. This would test to see that the transducer assembly is functioning. NOTE: there is a interlock circuit in the computer that if there is an issue with alt hold it will not allow you to select the mode and you will not get the annunciation of ALT on the bezel.

@Wingover There is a small dc motor that is attached to the drive motor inside the servo assembly. It provides negative feedback to the computer to tell it the direction of rotation and how fast. If the tach feedback motor is inop the servo will end up over driving causing a 1-2hz oscillation. Sounds like you might have a pitch servo issue. If part of the transistor bridge fails it will cause a hard pitch over or no drive in one direction. You can test this by using the UP/DOWN rocker in the computer to change the pitch attitude. You should be able to set a climb or descent attitude and the computer hold that attitude. When activating alt hold the computer takes the attitude information and the output of the altitude transducer to maintain a selected altitude.

@Wingover A slow drift, a oscillation, hard pitch up or down? If you have a video of the issue maybe that would help. Most common issue for a slow drift would be servo startup voltage, a 1-2 hz oscillation would be failed tach generator, a hard pitch up or down would be failed transistor drive.

Altitude hold information comes from the transducer that is internal to the KC192/KC191. Can you give more detail on what issue you experienced with alt hold in flight?

Base unit GI275's can be purchased over the count and installed by a AP. ADAHRS and ADAHRS+AP units need to be purchased via a Garmin dealer. Base units are typically used for CDI, MFD, HSI, EIS functions. They do not have the second connector that is used for legacy autopilot interface and do not have ADAHRS functions.

I would have someone listen to the motor speed when operating the trim system on the ground. If the motor is slowing down I would expect a increased load on the servo. If the load is too much eventually the slip clutch would start to slip. When was the last time the trim controls were inspected and lubed? Running trim by hand do you notice a area where there is increased friction? The servo would have to work against the increased load when using MET (manual electric trim). We have seen several Mooney's where there was excess friction causing the trim drive to slow when using MET. Cleaning and proper lubrication of moving parts tends to resolve this issue. If the motor speed doesn't slow I would expect a problem with the slip clutch assembly. I can tell you what the slip clutch torque limit should be if I have the model and SN of the aircraft. There is a slight possibility that there is a issue with the voltage regulator in the trim servo. Normally if the voltage regulator is soft the trim servo drive is very slow or INOP.

New GI275's come with a 10 hour trial of SVT. If you like it and want to add it there is a unlock that is needed. GI275's do a lot more vs G5 and interface with more equipment vs G5. Depending on the equipment in the aircraft the GI275 could have a advantage over the G5.

Make sure the installation shop you choose knows how to do the alignment to the KAP150. The process is outlined in the Garmin IM for the GI275 when interfaced to the KAP/KFC 150 system.

The only approved display replacements are the mod kits produced by Honeywell that change the old gas display to a led. Honeywell, continues to increase the price of this mod kit so it has become more costly to fix these units. We have had very few issues with the LED mod by Honeywell. There is another person that advertises an OLED replacement. However, this is not an approved mod, if you choose to do this good luck getting someone to sign off on the radio if it would need any future repairs. We have seen a couple of them come in and we have rejected the units due to no service data being available. The frequency knob issue is pretty common as these units continue to age. It is fairly easy to replace pending the parts are available and the repair shop knows what they are doing. With the repair cost increasing more people are replacing the units with new modern radios. The GNC215 by Garmin is a good option and you can buy them over the counter. We have installed several of them in multiple aircraft with no issues. The KX200 is advertised as the replacement to the KX155., but we have yet to see one in the wild. I have heard that the unit are finally available after being talked about for a couple of years. We still repair the KX155 units and have the LED mod kit available. The thing that really makes the units non repairable is when they have capacitor leakage and it spreads damaging multiple circuits in the radio. This capacitor issue is more common in units manufactured between 1991 and 1998.

@Guillaume see attachment. 006-00396-0000_4.pdf