A number of pilots have done this and found that the 165A works fine in the COM2/NAV2 position (driving a KI204 or similar) but does not work in the COM1/NAV1 position (driving a KI525 HSI).
The KI525 uses the converter inside the KX-165A. On older KX-165 their should be a wire jumper from receiver composite output, to composite input of the converter. On the KX-165A this jumper should be onboard.
The Sandel SN3500 and Aspen EFD1000 directly use this composite signal, just like the KI204. So they will never have this problem. The external converter KN72 shouldn’t be used for those installations.
My KI525 used a KN72 converter, but replacing the KX155A with a KX165A stopped the KI525 working.
This was the original issue, and was never explained.
I solved it by putting the KX165A into the COM2/NAV2 position instead, which had nothing to do with the KI525. So I got 8.33 without any issues.
It is quite possible that now I could swap over the two radios (I now have 2 x SN3500 EHSI which use purely the composite signals for VHF LNAV) and it would work fine. Maybe I should try it. But it doesn’t matter…
Based on the manual it should work. Never tried this myself.
It could be due to load. The KX-155A doesn’t have an internal converter, while the KX-165A has an internal converter which is always enable (the jumper wire used on the connector of older units is now inside the KX-165A. Using it combined with KN-72 means the composite signal is send to both the internal converter AND to the KN-72.
The composite output can be adjusted to give a higher output when required (due to a higher load).
Not sure if this is causing it, but it could be, as they also designed a way to increase the composite output.
Peter, I have installed a KX165A , Part.No. 069-01033-0201, as a direct replacement to a KX155A in the NAV 1 position. My HSI KL 525 works flawlessly without any adjustments. Hope this information helps. There must be some specific difference between TB20 and Cessna 182 which I am not aware off though both have the same radio and HSI.
Yes that’s useful info. Historical interest only to me, because my KI525 HSI is long gone.
Anybody with a KX155 or 155A and with a KI525 HSI is going to have a KN72 NAV converter. Once a KX165/165A is installed in place of the old radio, the KN72 is theoretically redundant but needs to be left in place unless some considerable rewiring is done to use the converter inside the new radio instead. But if you just plug in the new radio the KN72 will still be connected.
Jesse’s post above may well explain why that didn’t work for me. Presumably the composite signal output level can be adjusted in the KX165A’s config – Jesse?
The composite output signal can be adjusted on the KX 165A and I can see how you can run the HSI via the composite output if the KX165A but personally I would remove the KN72 and run the HSI direct from the KX165A, after all that is what it is built for.
I have found the KX165A to be a very good unit in terms of long range lock on to VOR stations and COM tx range.
The composite output signal can be adjusted on the KX 165A and I can see how you can run the HSI via the composite output if the KX165A but personally I would remove the KN72 and run the HSI direct from the KX165A, after all that is what it is built for.
I do agree, It’s best to keep the installation as simple as possible. However I can see that people would want to do this, as it saves quite some labour, AND it should be possible.
Presumably the composite signal output level can be adjusted in the KX165A’s config – Jesse?
Yes, this is what the manual says:
“VOR/LOC Composite Level (COMP) has a range of 0 to 255. The Level is factory set, and should not need adjustment. A setting 0 produces a minimum VOR/LOC level, a setting of 255 produces a maximum level. The VOR/LOC Compsite Level may be adjusted to interface with an external converter/indicator. "
I would say that normally it wouldn’t need adjustment (using the interval converter) and can be adjusted when required to have sufficient drive for a second converter, as you can’t switch of the internal one. (internal jumper)
The level might be right on the edge as it seems to work normally at highflyer.
The composite input of the KN72 is a fairly high impedance
Depending on which input is used, it is 7k, 60k, or 330k, approx.
On a quick and dirty look at the KX165A circuit diagram, the composite output is buffered so the above loads should not affect it at all.
Maybe I am looking in the wrong places?
Something must be different. One would think it has had issues with this, It doesn’t make sense to make the output it adjustable in software if it is signalstrength is always correct.
It would be interesting to see the difference on KN-72 TP101 between the KX-155A and KX-165A with if there is any (with valid NAV). It’s not a problem with your Sandel. Do you know the impedance of that one? The KN-72 should use the pin 6 input with the KX-155A / KX-165A
The SN3500 inputs are all high impedance – over 100k.
Pin 8 of the radio goes to the KN72:
I wonder if perhaps the composite output level of my KX165A was set too low, and maybe that is the ex factory (or ex factory/overhauler test procedure) default, and it happens to be too low for a KN72, but not too low for a KI204/KI229/SN3500. Actually my KI229 is switchable to NAV1/NAV2 but I don’t recall whether I tested it on both. Can the output of a KX165A be configured too low to drive a KN72?
