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ctfarmer

Garmin SL40 problem

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I have a Garmin SL40 and has just experienced the following problem.

 

During a flight, the Tx stopped working but the panel still displayed the dual frequencies. Prior to this issue the unit was working normally.

 

I terminated the flight and started to troubleshoot on the ground.

 

The following symptoms are evident.

 

·         Turn the power on using the circuit breaker or avionics switch and the dual frequencies display for about 1-3 seconds then fade or flash quickly away to nothing.

·         During the 3 seconds, the Tx appears to work until the unit goes off.

·         Once off as above, the unit has no working functions.

·         With power on the unit, using the units on/off control knob and nothing shows - the unit doesn’t turn on at all.

·          the head phones plugged in or unplugged, have no affect on the operation as above.

 

 

I have measured 12+VDC on pin 1 on the RS232 connector on the cassette mounting plate. I have negligible resistance to the ground/earth on Pin 9 (power earth) back to the busbar located on the passenger side firewall in the cabin. I have not checked the resistance from there to the battery negative terminal but did tighten up the bolts. Everything else works fine connected to that ground busbar and will check further tomorrow.

 

I suspect a ground or power issue but on the basis of the tests i have done, everything looks fine.

 

I will set up a 3-4 amp load and load test from pin 1 to pin 9 measuring voltage at the same time.

 

Anyone got any thoughts.

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Check all grounds. And make double-sure it is seated fully in the receiver, so that the connector is all the way in.

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Grounds were all fine. Was able to borrow the same radio from another aircraft. No problem with it in my cradle.

 

Opened mine and it smelled slightly of burnt electronics. One cap is clearly cooked. Very odd.

 

 

post-1065-0-26941500-1492329881_thumb.jpg

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SL-40 failed internally with over voltage to part of the circuit. Not reparable.

Installed a new Icom A220 radio. Looks to be, on the surface, far better made and engineered.

However, for the entire duration of my first flight, i had what appeared to be a squelch problem - could not be set to overcome noise. Turned out to be a 12V to USB socket adapter i had running my Ipad plugged in in close proximity to the radio.

Easy fix once i found the cause and it is a much nicer unit to operate. As well, looking at its design and manufacture, the cast aluminium chassis for example and general feel of knobs, i have far greater expectation it will be more robust electronically.

 

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Seems unusual, in my neck of the woods the SL30/40 radios have a great reputation for reliability.  

Good luck with the Icom, those radios look very nice indeed.

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I pulled out a SL-40 Last week from my CTSW because here in the UK we all have to have 8.33Khz spacing and I installed a Icom 220 and agree with Ctfarmer it does look and feel a lot more robust, I haven't flown it yet but my iPad is plugged in via a USB port next to the radio so I will listen out for the squelch problem.

I now do have a working Garmin SL-40 if anyone wants one as it is of no use to anyone in Europe now.

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To add my situation to problems with the Garmin SL-40, on my last two flights I have got a lot of background static/noise when I transmit. Both push-to-talks on pilot and passenger control sticks have the problem. Other aircraft have confirmed the 'noise' on my transmit. Reception seems okay. Swapped out headsets, Tango to Zulu to DC.... no change in condition. I will try to play with connections in back but I am in the dark... any advice on this would be appreciated... thanks

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1 hour ago, cgrbu said:

To add my situation to problems with the Garmin SL-40, on my last two flights I have got a lot of background static/noise when I transmit. Both push-to-talks on pilot and passenger control sticks have the problem. Other aircraft have confirmed the 'noise' on my transmit. Reception seems okay. Swapped out headsets, Tango to Zulu to DC.... no change in condition. I will try to play with connections in back but Im in the dark... any advice on this would be appreciated... thanks

Do you have the Intercom Bypass plugs installed?  Have you tried going directly thru them?

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I am not sure if the two additional plugs below my PFD Skyview is what you are referring to?

 

 

 

 

Powered Panel.jpg

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I have tried that long ago but not recent...when I did use them it isolated the passenger system... I will give it a go.... also Tom (a.k.a Roger :) ) Lee has made some good suggestions that I will address this week-end, (gnd, tray and if all fails, bench test)

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I have also noticed recently when intercom is on I get a buzzing sound that I think corresponds to the beacon light cycle which is an LED type. I do not notice that when intercom off (no pxx)

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I have not had avionics on without engine running, I will do a static test next and record the results...also will test when running, gen cb out...

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before taking SL40 unit out of tray, tested before starting engine, transmission and reception clear as a bell. Did a quick removal checked pins for damage and re-installed. Did a start up and on initial transmissions had the static. Went flying and with higher power settings transmission okay, back to the barn and static not noticed on ground taxi... will see what happens on next flight....thanks to all who have had some suggestions

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to answer coppercity ...today the noise is as loud as before when hooked in to jacks behind pilot/pxx seats and with gen circuit breaker out, no change (engine running). I have had those jacks out and checked for corrosion (emery papered, but I may swap them out for new). I get perfect transmission and reception when I am hooked directly to forward panel jacks (see picture attached). I have added the extra gnd wires from Battery to #3 cylinder and back to the starter solenoid which has the ground wire connected to the interior gnd bus. Also I have installed new spark plugs NGK DCPR8E 4339 gapped at .028. 

PFD panel and jacks.jpg

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Those forward jacks are isolated from the intercom, and just go to the radio. If it is quite there your problem is not the radio, the noise is coming from or through the intercom. Something I have done before trouble shooting noise in the CT is to pull each breaker independently to see if one specific piece of equipment is causing the issue. I had one whos noise was created by the GPS. After installing a ground loop isolator the problem went away. 

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thank you both for the comments... I will target the intercom. As well the mention of the GPS has me thinking of the recent problems I have had with it not coming online with the start-up. I had the centre console out a couple of times to ensure that the power cord is properly seated and I also shimmed the antennae feed at that time so it would not work loose. With your mention of the ground loop antennae, is that a part you can order from Garmin or an avionics shop?

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additionally I believe the autopilot servos may have been engaged while on the ground as my control stick has moved with a clicking sound. I pulled the circuit breaker for this as well to see if the noise would stop on the radio transmission, no change.

 

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The PM3000 intercomms do not filter electrical noise very well. In addition, the choice of wiring used for audio leaves a lot to be desired. Hell, on other aircraft I have even seen untwisted wire used in some installs, it's embarrassing!

Twisted wire does a substantial job to noise filtering when in close proximity to other wires that have fluctuating power. Outside of that, the switched mode power supplies used on many of the LEDs on flight design aircraft are garbage and have horrible RFI filtering, and that also likes to propagate back through the system.

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