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MGL Avionics Troubles


Looking for input on how to proceed with multiple problems I have been having with MGL Avionics installed in my experimental Cub. I have a MGL Challenger Lite EFIS with their support boxes and radio. The first problem popped up in the initial powering up of the panel with the master switch on the electronic circuit board (ECB) which does a staggered timed start for each circuit wired into the box. Turning the avionics switch on will sometimes start all the avionics, sometimes start some and no telling as to which will turn on and which circuit does not get power except the paired radio/intercom will be either on or off. The MGL service rep had never heard of this before. The mechanic that wired it says to leave the avionics switch on and then turn on the master switch which then "works around" the problem and the panel avionics do come on all the time except two flights ago and will get to that.
Close to time for the airworthy inspection the MGL avionics panel failed in that it would not turn on at all. MGL had me return the EFIS for service and a power rectifier was replaced on the main board under warranty so just my expense to ship. Twenty hours into the new aircraft flight time, 2 MGL provided EGT probes came out of the exhaust stacks they were installed in and the MGL service rep said "you can't bond them back in place you need to spot weld them". The first option showed me a lack of understanding and I attempted to spot weld the EGT probes to the hose clamp style bands with expected results of dead probes. I have JPI engine monitors in my 2 other aircraft with no issues so purchased a set of 4 JPI probes and replaced the dead ones which corrected this problem. Now to the EFIS quitting in flight, two flights ago after taking off from a friend place the EFIS went dark, with multiple resetting the master and avionics switches the same problem popped up with partial power to the avionics and some times the radio/intercom would turn on and sometimes it would not with the EFIS power coming back on some 15 to 30 minutes after landing and putting the aircraft in my hangar. I contacted MGL via email and explained what happened and power interruption was given as the explanation. The last flight upon shut down had the EFIS and avionics panel functioning but there was now a new noise coming from the EFIS which sounds like a fan motor going bad. On the same last flight now CHT #1 is fluctuating up to 100 degrees with stable EGT temperature for cylinder #1. I have replace the errant CHT probe but hesitant to fly the plane again with likely failing fan motor in the EFIS. I have sent 4 emails to MGL service on this and one phone call today with no response so looking for help from anyone who might have some experience with these issues.
Thanks in advance.
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Ugh. I hate this part of the business. I.e. trying to make sense of something the factory should be working on.

With the fluctuating CHT temp, it sounds like just a bad connection. Check the connectors from the probe to the wiring.

Not so sure about the power problems. Start with the most basic stuff. Unplug the connectors and ring out each power and ground wire. Make sure no one did any shortcuts or cute stuff with the connections, especially the grounds. Frying a rectifier is some major stuff as it usually requires a reverse polarity connection or a large over current.

Check all connections at collective grounds and at the bus bar/breakers. Check for spike diodes on all relays also.

I'll check the diagrams and see if I can find any common points to trouble shoot.

Ok. Can you give me a description of how the harness for these items is installed and terminated? In MGL's info, there are numerous instructions on how to set up the powers and grounds. How is your power bus set up? Do you have the EFIS system on it's own ground point? MGL even states that the ground point needs to be connected directly to the battery ground point by it's own cable. Did you do that? Do you have the EFIS wiring bundled with other airframe wiring? Are any coaxes bundled with them?

A few years ago I swapped out my VAL Avionics com radio for the dinky little V6 MGL. It works well enough, though I liked the 3 different VAL's I had in my last 3 planes better. But I don't need or use a radio that often, and I saved several pounds (counting the VAL's installation tray, hardware, etc.) and gained panel space. Lightness takes priority with me.
I'm going to have to remove the windshield and top boot cowling to check all the panel wiring which I built the plane for this access, just did not think would need to do so soon. I did not do the panel wiring will take me a bit to get up to speed on the layout once I get access.

The panel wiring was complete and avionics on with me not touching anything sitting in the front seat reading the manual when the EFIS died the first time. The panel was on battery power run through a B and C, LR3D-14 regulator, the engine had not been run at all so I don't understand how an overvoltage could occur to cause the power rectifier to fail on the EFIS.
Web, Thanks for the guidance.
On a side note MGL responded this morning and there is no fan motor in the EFIS so not possible to be making noise from the there per the tech.
That B&C regulator is for the alternator not the battery.

An overvoltage is not the same thing as over current. Current (amps) is just the flow of electrons, like water through a pipe. Voltage is just the pressure that makes the electrons flow. With battery power only, the voltage is fixed but a short circuit due to improper wiring or reversed connection will still result in an over current situation. In simplest terms, that 12 volts from the battery pushed more amps through a component than it was designed to handle.

Just off the phone with the MGL service tach and apologized to him as there is no fan in the EFIS so the sound was not coming from there, the electric boost pump switch had been bumped on and was the noise, my mistake. I was primed for problems since having to return this unit 3 months ago for service and having the partial power problem from the get go as well as other issues not addressed in tis post. The tech had suggested that the ECB soft start could be having issues when two devices were ganged to one terminal to power which in my case is the radio/intercom which is possibly causing the ECB to not power up properly. I tested this by turning off the intercom and then cycling the master on, then avionics switch, on and no partial power problem. That leaves me to rewiring the ECB and check grounds when behind the panel. I thought I was treating myself with the glass panel but more complicated than I needed and I am finding I am not well suited to working on something I do not understand.
If you haven't read through this troubleshooting guide, you should take a few minutes and read it. Lots of points pertaining to MGL units.



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Are you using a battery backup/power conditioner for the EFIS?

I have no conditioner or backup battery for the MGL EFIS. After the inflight failure of the EFIS with no primary flight data as the screen went completely off and intermittently the power was interrupted to the paired radio/intercom circuit from the ECB I ordered a Garmin G5. My plan now is to eventually remove the MGL system as failure is not an option for a primary flight system and replace with reliable engine monitor and instruments not prone to glitches or out right failure. Working out the details and will be a major undertaking and ground the Monster Cub for a while. I lost last summers flying season to the system partial panel issue needing a fix which did not happen and should have gone with my gut feeling to scrap the panel after the EFIS quit the first time and had easier access to the panel. For others to consider putting in a system like this they are very complex and lots of areas to have problems even if done correctly. Experts like Web show their worth if venturing into this arena. Will mention the MGL raster maps are nonexistent for Alaska and the sliver than a friend loaded into my system does not locate the aircraft in the correct area and I am clueless as how to program the computer, believe me I have tried.
I have units that I like and ones that I dislike and I'm not shy about it. But if you get sand in your skivvies because I express my disdain for some component you installed, stop for a moment and find out WHY I don't like it.

In this case, read any of MGL's installation instructions for ANY of their units, especially for the wiring. Although there are some rules of thumb that go industry wide, such as not bundling audio or data cables with high current wires or not bundling coax cables at all, look at what MGL requires. Conditioned power inputs. Requiring grounds to be isolated from the airframe. Ferrite sleeves on some power wires. Then look at the same requirements for items like G5's or AV-30's or avionics items like intercoms and radios. No requirement for conditioned power, grounds separate but to the airframe, and be careful how you bundle.

None of the MGL requirements are 'head scratchers' or especially unreasonable, but they take more time to comply with on installation. This means more cost for installation or repairs. This also leads to more complexity. Compare the power/ground connections for MGL EFIS systems to a G5. MGL wants a power conditioner on the bus power supply to provide smooth, spike free power to their unit. They also want a separate bus to provide power just to the MGL and it's connected equipment to prevent fluctuations in voltage when other equipment is turned on/off. This means the installation of a power conditioner (fancy power filter) and running wire from the master relay to the EFIS bus, in a separate circuit from the normal bus power. Then MGL states that they want a ground bus just for the EFIS system, isolated from airframe ground, wired back to the point where the battery ground attaches to the airframe. If I install most other brands of instruments/avionics, like the G5, I provide power, through a breaker, from a common bus and connect ground to a point on the airframe, in common with other avionics or instruments.

Less complex means less money and easier maintenance, so take a moment to check out the installation instructions for the new, cool unit you want, as they might steer you in a different direction.

There is a reason TSO units cost more, environmental testing, software safety, and a lot of other things that relate to reliability cost money to design in during development.

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I agree, except that there are many non TSO'd units out there with simple installation requirements. In MGL's case, my opinion is that it is incomplete engineering or possibly designers with little or no aviation background.


Less complex means less money and easier maintenance, so take a moment to check out the installation instructions for the new, cool unit you want, as they might steer you in a different direction.


I could not have stated this better, Thank you Paul. I have two other aircraft with simple electrical systems, with one I wired from scratch and I’m able to maintain mostly trouble free for several thousand hours now.
I think this situation is a shame. My G3X Touch is a joy to fly with.

Re: power conditioning? Garmin recommends it. I have nonidea what the other mfgrs say. I have surge protectors and battery backups on my computers. It sucks to have a power interruption and lose your work unexpectedly. Why would anyone ridicule using one in an aircraft? Battery backups are required for TSO units. Power buffering just makes sense. I have no idea if that’s a factor in LiteCub’s issue but I’d like to see the problem resolved so he can enjoy that airplane.
Point one - Power conditioners simply smooth out any dips and peaks in the DC input voltage. On the surface they makes sense. But if you design equipment that uses power from a source such as an engine driven alternator any conditioning should be built in. Momentary dips in voltage and fluctuations with varying loads and engine speeds are continuous in that environment. What engineer would NOT design the conditioning circuits into the unit. Relying on external circuits sounds like someone put out a poor design. You'll have a hard time finding mainstream avionics that require them.
Point Two - Backup batteries are not a requirement for a TSO. Great idea and I always recommend them, but they are optional on most equipment.

Glad you like your G3X. It's a cool unit.

The latest MGL fun... while returning from a flight yesterday while trying to get a new OAT temp probe to register I reset the airspeed inflight to ZERO. No way to get it back while in flight. Last night while reviewing my logged time in ForeFlight for N90AK total of just over 40 hours now. The MGL EFIS has 4 timers with none of them matching up and the most is on the Hobbs at 37 hours. Should be no problem as the user can just change at will any of the times to any value needed. The panel will be getting a real tach with hour timer in it ASAP so will have accurate record of time on this aircraft.
I have an MGL radio in Bushwacker, it sucks. I have had it back to them multiple times. I would not buy anything MGL.
I fixed the MGL avionics by removing them last winter. Have 25 hours now on the new panel and big stress reliever in ease of us now with the Garmin avionics.


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Not my cup of tea, but a friend just bought a Chief with a battery powered MGL comm radio - two parts, control head and separate transceiver box. It proved intermittent, with the control head screen going blank at one point (grey screen, so still powered). Battery only, so first thing I checked was the battery voltage. 13 1/2 Volts, as I recall.

Contacted customer service - they couldn't offer any opinions without a model # (I guess they make so many different coms . . .) so I copied the numbers off both boxes and forwarded them. Haven't heard since.

Not my airplane - I am just one of the instructors. If it was my airplane I would put a GTR-200 in it long before I would bother further troubleshooting (at $125/hr). I would then send it (the MGL) to Paul for postage.

Postage to Alaska is now frightening!