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Update, and, Encoder


chrixxer

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So ... The Mooney is as put together as she's going to be for right now. The stormscope (WX-1000) works. The autopilot (S-Tec 30) works and is connected to track VOR/LOC or GPS (deviation only, not GPSS); Tucson Aero performed an internal repair on the S-Tec computer (a plastic universal joint was bad; $70 fix). The Garmin SL30 (sourced from a MooneySpacer) works great, and my non-standard install (DB25 pass through in line between the PM2000 intercom and existing headset etc. wiring, with milspec multiconnector wiring split off to patch in the SL30; no audio panel, for now, though I have a GMA340 ready for install) is signed off and blessed. Weight and balance was updated. The to/from flag assembly on the well-used IND-351 I also got off a MooneySpacer (for pennies) had failed*, and TA wouldn't work on the old plastic Collins stuff; PSI would ($700 at the top end) but between that and the new hole they were going to have to put in the panel for a back course annunciator light to be fully IFR legal wasn't worth it to me; I sourced a pristine MD-200-306 on eBay for $1300 (mid-range for what they're going for, and well under what Wentworth is quoting for a used unit). The repaired GX55 is still working great, and as long as the track doesn't change more than 10° or so at any given waypoint, I can fly long distances without touching the controls. Next up will be a panel redo with engine monitor, and probably Garmin G5s (though that might wait for the GPS install).

But the immediate need is a blind encoder.

I keep losing my Mode C (but not the Mode A component) on my transponder, a new-to-me but tested working pristine KT76A. Tucson Aero checked connectors, wiring and the encoder to 16 k/ft hot/cold as a system, and never saw a problem (while noting via email that the encoder in there now "is a Narco  Gillham and that would be suspect at this time"). I'm going to have the encoder swapped locally. I was looking at the SSD120-35C-RS232, which TA says is as good as any other selection. It's RS-232 (future) and grey code (KT76A), and, cheap ($215).

A self-styled avionics guru at the local FBO vehemently suggested I go with the SSD120-30N-RS232 instead ($349), and that the 35C was a "piece of junk."

Any opinions? Alternatives?

(Still not sure if I'll go GTX-345 or just slap a GDL-82 on the back of the KT76A...)

It's been a trip so far: https://drive.google.com/open?id=0B3wWtj5n3Y6QQTFhUV9CdG1IV3c I have 63.4 hours in her at this point, despite it being down for a month with no radios (expected when I bought it; the Terra equipment was prehistoric), then down for a week with a flat nose tire (sigh), then in Tucson for six weeks.

‡ When I fix up the interior, I'll run new wiring that will work with the Garmin audio panel, and when I have a second source of audio (GTN-650), I'll install it along with that hardware.

* But it enabled me to fly a couple of critical Pilots n' Paws missions in actual IMC down to minimums before it died, so, several rescue dogs say "thanks!"

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Not sure I follow. The dial on the CDI should not change the course signal between the gps source and the AP. I think in most installations moving the cdi course dial has no control over the course deviation needle when using GPS. 

Do you have a switch between the sl30/gx55 and the CDI or does the unit switch them for you?

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There’s an A/P NAV switch to go between the SL30 and the GX55. Here’s what the S-Tec manual has to say (lightly edited):

 

VOR/LOC:

1. Tune the NAV receiver to the desired Localizer frequency.

2. Set A/P NAV select switch to NAV1.

3. Maneuver the aircraft to within +/-1 needle width and within 10° HDG of the published inbound localizer course or VOR radial.

4. Press and release Mode Select Knob until HI-TRK lamp illuminates.

 

GPS Tracking and GPS Approach

1. Enter desired waypoint in GPS receiver.

2. Set A/P NAV select switch to GPS.

3. Maneuver the aircraft to within +/-1 needle width and within 10° of the course displayed on the GPS receiver.

4. Press and release Mode Select Knob until HI-TRK lamp illuminates.

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(The GX55 has a built-in CDI; it should be connected to an MD-40 with annunciators to be IFR legal, but since it’s going away soon and isn’t an IFR approach GPS (only en route), I just use it for SA / DME / VFR autopilot (e.g., SMO to user defined waypoint VPLSR for the LAX miniroute), and navigate using the radio.)

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