MGL Stratomaster Enigma

[peter young]

Good afternoon all,

I own and fly a Savannah S based in Zambia. I have two problems with the instruments that i am needing help with.
1. The plane is fitted with a MGL Stratomaster Enigma. It works perfectly well in all regards except that the AH and Turn Slip work intermittently. A large red X appears on the AH and TS periodically. All the engine info, the GPS etc work fine all the time. Has anyone else had the same issue? and is there an easy fix?
2. The plane is custom fitted with a TRT800 Filser ATC Mode A, A-C,S Transponder. ATC only picking up a primary signal. The transponder is not indicating any faults but the tower are not getting any signal from me. I sent the transponder down to Dart who serviced it and said it was transmitting when they did a bench test. My plane has just over 200 hrs on the air frame so still new. Any ideas?

I would be very grateful if any one could shed some light.

Many thanks.

Pete Young.

[rainier]

On the Enigma:

Your AHRS connects to the Enigma using a RCA Video cable. There is also a small flashing LED on the AHRS that tells you if the AHRS is supplied with power and working.
The first thing to do is - when the Enigma shows the cross, check if the little light is flashing. If not you most likely have an intermittent power supply to the AHRS. If it is flashing then wiggle the video cable at each end - if your video cable has molded plugs - sometimes the cable connection inside the plugs fails. Also, some cheaper makes of RCA plugs have little finger like metal tabs that hold the plug and provide the ground connection - pull out the plugs and bend those fingers a bit towards the center pin so they hold tight and make a good connection. Also check for corrosion around the plug and socket. Do the same on the AHRS side. Undue the DB9 connector and check for corrosion.

[rainier]

2. The plane is custom fitted with a TRT800 Filser ATC Mode A, A-C,S Transponder. ATC only picking up a primary signal. The transponder is not indicating any faults but the tower are not getting any signal from me. I sent the transponder down to Dart who serviced it and said it was transmitting when they did a bench test. My plane has just over 200 hrs on the air frame so still new. Any ideas?

I would be very grateful if any one could shed some light.

Many thanks.

Pete Young.

This is a bit confusing - you say the tower picks up a primary signal but in the next sentence you say the tower is not picking up your transponder ?

Do you perhaps mean that the tower is seeing your mode-A reply but not your mode-C ? If that is the case make sure you have switched your transponder to altitude mode (that enables mode-C response that contains your altitude). Mode-S is likely not used in your region - does not matter, your transponder will not send a mode-S reply unless it gets the required mode-S interrogation.

There is no "primary signal" in a transponder reply. Hence the uncertainty of my reply.

[heisan]

There is no "primary signal" in a transponder reply. Hence the uncertainty of my reply.

Primary return is a reflected radar signal - not a transponder response - i.e. they are not seeing the transponder signal at all. Probably an antenna/cable problem with the transponder.

[peter young]

Thank you both for your replies.

I gather the tower are getting nothing from my transponder....just seeing the reflected radar signal. I have checked antenna and cable and all looks good. If there is a fault on either it should show up as a fault on the transponder screen which it is not.

On the MGL Enigma. Please forgive my ignorance, but what does AHRS stand for? and where is it? I have fiddled with connections behind the Efis and it helped for a while but the problem has started again. It sounds like you are on the right track though.

[Chalkie]

Thank you both for your replies.

I gather the tower are getting nothing from my transponder.

If someone made up the coaxial cable from transponder to antenna, then there is a possibility of a short in the coaxial cable. All it takes is one wayward strand from the shielding to contact the centre wire to cause a short. This can be checked with a multimeter, just disconnect both ends of the coaxial cable and check for continuity between centre cable and the shielding. It should be an open circuit IE: no continuity.

AHRS is Attitude Heading Reference System: IE: the solid state gyro, Rainier can advise where to look...

[rainier]

There is no "primary signal" in a transponder reply. Hence the uncertainty of my reply.

Primary return is a reflected radar signal - not a transponder response - i.e. they are not seeing the transponder signal at all. Probably an antenna/cable problem with the transponder.

Ah yes of course.
Well since your transponder has been bench tested as OK - the only thing left it your antenna and cable. Not much more to it. Antennas do not really fail so check the connections - not just eyeball - measure them with a ohm meter.

[rainier]

AHRS is Attitude Heading Reference System: IE: the solid state gyro, Rainier can advise where to look...

Well, should be somewhere around the center of rotation of your aircraft. Perhaps under the seat or something like that.
Could be a SP-3 - look for a gray box about 10cm long. Could be an SP-4 - not much bigger than a matchbox, black. Or perhaps a newer SP-7 - about 9x7cm in size also black. All of these have a flashing LED if they are powered and working.

[peter young]

Thank you all for your help.

That has given me something to go on, both with the transponder and the efis. Will report back if i make progress tomorrow.

Cheers.

[fll]

Thanks for starting this discussion , same problem here , I took the panel apart this morning , the red light is flashing very fast couldn't find corrosion , will be trying a new coaxial cable but I'm wondering if on a rainy boring day the fingers did some exercise and changed a setting ? Any particular important settings to look out for ?

[fll]

I fitted a new coaxial cable but the 2 red X's are still there permanently , I can see the highway in the sky and if I move the ahrs the highway moves as well ?

[peter young]

Good morning all,
I checked under the seats and low and behold there was the AHRS. It has 2 x black boxes both with flashing red lights. So the AHRS seems ok. Looked behind the efis and found that there are 2 cables, one orange and one purple that come from the efis and join onto the grey video cable. Maybe that joint is dodgy. Will check it out today.

Am wondering whether you fll have 2 cables joining into one like mine?

[fll]

Good morning, no only 1 cable, it's plugged in closest to the big plug

[peter young]

Making progress!!!!! Down loaded the Enigma Installation manual and with that and all your help on this forum, discovered the cable to the AHRS was plugged into the wrong socket. Changed it into the right socket and hey presto.......every thing working perfectly.

Just the transponder to fix now.

[Jean Crous]

Aha !! Then to the original installer ...."RTFM !! "
Jean