mobilepolice
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I have a KI-209A in my Cherokee that has always had an alignment issue with the VOR and the OBS card. The instrument tracks an ILS perfectly, and it follows a VOR perfectly too, except the OBS card is exactly 34 degrees to the left of the actual radial when the needle is centered with the course.
I've got a friend who's been flying the cherokee for me since I've been trying to sell it and while I'm selling it as a VFR-Only airplane (because that's all it's really equipped for) he's a bit of a stickler about the CDI being off. There's a second CDI in the airplane that's VOR-Only (an old narco with a built-in radio) and it works fine.
I took the Cherokee to an avionics shop near here and paid for them to pull the radio and the instrument and diagnose. Based upon it's behavior, I was pretty sure it was all in the CDI and that the OBS card just needed to be aligned with the electronics. the 34* offset to the radial was all the way around the card, so it stunk like just a card issue.
They told me that 34* offset is huge, and that "the pot inside the CDI really only has 15* of adjustment one way or the other, so I doubt we'll be able to take the error out, but we can diagnose for approximately 3 hours shop labor"
I didn't know anything about this particular CDI before I took the plane in, and I didn't have time to do any research or find any service manual. I TRY to educate myself and diagnose before I go to an expert so that I can at least understand their explanation, but here's the return phone call I got:
"Something is bad-wrong inside the instrument, we're seeing 6.5K ohms resistance on two pins when we should only see 2.5K ohms, so we're not sure why that is but our guess is the sensor for the OBS card is bad and that's not an easy-to-get part, so to replace the CDI with a used unit that I just put on the shelf yesterday, it will be $1300 and we'll cut you a break on the labor and a small shop fee should get you out the door for approximately $1500"
I'm not keen on throwing money at used old parts unless there's a good reason for not upgrading to newer parts, so I told them to put the old KI-209A back in the plane and I'll deal with it/and or get a second opinion.
Just as I was going to bed last night it occurred to me to look for a service manual and I found this:
http://www.csobeech.com/files/KI209A_Maintenance.pdf
Page 55 section 5.2.3 SIN-COS POT/AZIMUTH CARD CALIBRATION
It very well may be that they performed these steps, however the instrument back in the airplane has exactly a 34* offset and I gather that by following these instructions that would have changed. The amount of offset is irrelevant, because the external card is rotated to match the internal electronics. The only time that this would not be possible is if the needle was offset from the radial at different degrees around the card. This is not the case for my CDI.
Can someone give me a second opinion here? Are they blowing smoke up my ass just trying to sell me something I don't need, or is there really some sort of "internal trim pot" that has a limit to adjustment with regard to the OBS card?
I'm dependent upon others about this information because I don't really have anyone but this one avionics shop locally, or sending the instrument off to be "overhauled" for something that looks like a 5 minute bench adjustment.
Thanks for reading.
I've got a friend who's been flying the cherokee for me since I've been trying to sell it and while I'm selling it as a VFR-Only airplane (because that's all it's really equipped for) he's a bit of a stickler about the CDI being off. There's a second CDI in the airplane that's VOR-Only (an old narco with a built-in radio) and it works fine.
I took the Cherokee to an avionics shop near here and paid for them to pull the radio and the instrument and diagnose. Based upon it's behavior, I was pretty sure it was all in the CDI and that the OBS card just needed to be aligned with the electronics. the 34* offset to the radial was all the way around the card, so it stunk like just a card issue.
They told me that 34* offset is huge, and that "the pot inside the CDI really only has 15* of adjustment one way or the other, so I doubt we'll be able to take the error out, but we can diagnose for approximately 3 hours shop labor"
I didn't know anything about this particular CDI before I took the plane in, and I didn't have time to do any research or find any service manual. I TRY to educate myself and diagnose before I go to an expert so that I can at least understand their explanation, but here's the return phone call I got:
"Something is bad-wrong inside the instrument, we're seeing 6.5K ohms resistance on two pins when we should only see 2.5K ohms, so we're not sure why that is but our guess is the sensor for the OBS card is bad and that's not an easy-to-get part, so to replace the CDI with a used unit that I just put on the shelf yesterday, it will be $1300 and we'll cut you a break on the labor and a small shop fee should get you out the door for approximately $1500"
I'm not keen on throwing money at used old parts unless there's a good reason for not upgrading to newer parts, so I told them to put the old KI-209A back in the plane and I'll deal with it/and or get a second opinion.
Just as I was going to bed last night it occurred to me to look for a service manual and I found this:
http://www.csobeech.com/files/KI209A_Maintenance.pdf
Page 55 section 5.2.3 SIN-COS POT/AZIMUTH CARD CALIBRATION
It very well may be that they performed these steps, however the instrument back in the airplane has exactly a 34* offset and I gather that by following these instructions that would have changed. The amount of offset is irrelevant, because the external card is rotated to match the internal electronics. The only time that this would not be possible is if the needle was offset from the radial at different degrees around the card. This is not the case for my CDI.
Can someone give me a second opinion here? Are they blowing smoke up my ass just trying to sell me something I don't need, or is there really some sort of "internal trim pot" that has a limit to adjustment with regard to the OBS card?
I'm dependent upon others about this information because I don't really have anyone but this one avionics shop locally, or sending the instrument off to be "overhauled" for something that looks like a 5 minute bench adjustment.
Thanks for reading.
