NicoN Posted July 29 Report Posted July 29 A couple of days ago, I was forwarded a beechtalk newsletter, where on topic is something about GI 275s and Century A/P The beechtalk.com website is not available at the moment. I was pretty electrified , that there was information about problems with GI275s an some Century A/P, e.g. the 21 model which we have. Since the GI 275 was installed we have intermittent trouble but only with the HDG-mode. Everything else is working fine (more or less). It seems that especially under high temperatures, the A/P stop reacting on changes on the heading bug. The A/C then simply flies straight on the last heading (of course starts deviating). It is a wing leveler only then. Sometimes the HDG mode comes back by opening the ventilation air. Sometimes you can kill this function by switching on cabin heat. In the failure case, I can measure a voltage of 4.77V on the heaidng error signal inside the A/P controller! The beechtalk newsletter says something to install a 1kOhm resistor to improve impedance and avoid "power fault " messages. For our C21 this is even warranty reimbursed! To be honest: I have never seen this message, but I am pretty interested to see WHERE this resistor is installed. I am afraid, the newsletter does not giv any information about that! I do not even find a SB about that, rather than an installation manual with the necessary information. Has anyone additional information ?
LANCECASPER Posted July 30 Report Posted July 30 15 hours ago, NicoN said: A couple of days ago, I was forwarded a beechtalk newsletter, where on topic is something about GI 275s and Century A/P The beechtalk.com website is not available at the moment. I was pretty electrified , that there was information about problems with GI275s an some Century A/P, e.g. the 21 model which we have. Since the GI 275 was installed we have intermittent trouble but only with the HDG-mode. Everything else is working fine (more or less). It seems that especially under high temperatures, the A/P stop reacting on changes on the heading bug. The A/C then simply flies straight on the last heading (of course starts deviating). It is a wing leveler only then. Sometimes the HDG mode comes back by opening the ventilation air. Sometimes you can kill this function by switching on cabin heat. In the failure case, I can measure a voltage of 4.77V on the heaidng error signal inside the A/P controller! The beechtalk newsletter says something to install a 1kOhm resistor to improve impedance and avoid "power fault " messages. For our C21 this is even warranty reimbursed! To be honest: I have never seen this message, but I am pretty interested to see WHERE this resistor is installed. I am afraid, the newsletter does not giv any information about that! I do not even find a SB about that, rather than an installation manual with the necessary information. Has anyone additional information ? @Jake@BevanAviation
Jake@BevanAviation Posted July 30 Report Posted July 30 (edited) 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 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. Edited July 31 by Jake@BevanAviation 1
NicoN Posted July 31 Author Report Posted July 31 To be honest, the installation of our GI275s was not "flawlessly". First, the installer could not go through the calibration process for the GMU11. We could solve this problem, but then the A/P did not react to the heading bug as expected. It turned out, that the C21 flight controller was still jumpered for using a DG, but the GI275 "talks" HSI. It was not easy to convince the installer of what ist wrong, but finally it worked. Our C21 was working absolutely fine before the GI275-move, but is still not completely fine. 1. NAV/APPR mode is always working ( a little of center, but working) 2. HDG mode is always while the A/C is in the hangar. 3. Sometimes HDG mode stops working while in flight or while taxiing. In the air, the A/C is simply flying straight and wings level, like a wing leveller not reacting on the HDG bug. 4. Sometimes the function comes back shortly after landing. 5. It seems to be related to temperature. On real hot days it did not work. Last weekend I did several flight each 2h and it worked perfect. My first suspicion was a faulty connection from GI 275 (heading error) to the C21 flight controller. I followed the signal from the connector Pin 17 to the upmost PCB (it is a stack of 3 PCBs and soldered a little cable to measure the signal. If anything works, I can measure a voltage of 0... 9,7V, depending on the position of the heading bug (max to the left is 9.7V, max right almost 0V, or vice versa). in the middle position the voltage is around 4.8V (half of 9.6V). So, exactly as you posted it. If the HDG mode stops working, I measure 4,77V on this Pin 17 and it does not change with moving the heading bug. Of course, this can be a phantom voltage which does not come from GI275, but from the flight controller itself. So, the faulty connection is not completely ruled out. I was lucky, to buy a C21 flight controller for almost nothing on ebay, which is only partially working. The C21 Flight controller has 3 stacked PCB which are folded and connected with ribbon cable. The upper 2 can be easily removed while the bottom one is together with the front panel and the housing - so i call it the "chassis" - Our flight controller was bench checked as fully working - i was not possible to "provoke" the failure with a heater in the footwell - the misbehaviour happens also if I change the upper 2 stacked PCBs to the ebay chassis. So, a problem can still be on the upper 2 PCBs @Jake@BevanAviation: Can you give me additional information about that "routing" IC? All the ICs are thru-hole chips which are availbale via digikey, but there are many chips to change. So, a lot of work. Most of the chips are 4xAND, NAND, OR, NOR chips. Still, I am not sure that the GI275 is NOT the reason. At least, I can confirm that the HSI becomes not more than handwarm. Is the PFD with ADHARS-AP running hot? I am also not sure, that the AP HEADING ERROR LO signal is connected correctly.
Jake@BevanAviation Posted July 31 Report Posted July 31 The Century 21 MM calls has the IC listed as a MC14016BCP (quad analog switch) or a Century PN of 48S114.
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