Issue with Voyager EFIS GPS.

[JimJab]

Hi All,

I am having an issue with my Voyager EFIS, the GPS keeps dropping in and out. It's never done it before and just started.

I get an EFIS voice alert "GPS not available" and then a seconds or two later "GPS available" I can see on the EFIS screen the GPS has dropping out.

I also have a second Voyager EFIS in the plane and this is solid and does not dropout.

I am thinking the GPS module must be working and holding the required satellites, otherwise the GPS could not drop in and out so quickly.

So could it be the data from the GPS module to the EFIS mother board is being lost and the problem is the data cable and/or the connectors between the EFIS mother Board and GPS module?

Thanks for any experience or help anyone can give me.

Cheers
JimJab

[sparxfly]

Swap GPS modules and see if the problem shifts with themodule or rmains with the EFIS.

[JimJab]

Swap GPS modules and see if the problem shifts with the module or mains with the EFIS.

Thanks sparxfly for your advice, it sounds like the GPS is on it's own module board.

So I will pull the instrument panel out of the plane, I am guessing there will be a cable (ribbon type) between the GPS module and the main EFIS board? So can do a continuity test on the cable to see if it has a fault and reseat it back into the board connectors.

Here's hoping it something simple like reseating the ribbon cable or just replacing the cable.

sparxfly, thanks for letting me know it a GPS module, as it's good to have an idea of something before you start pulling you instrument panel apart.

Cheers
JimJab

[sparxfly]

A bit of miscommunication- I meant the GPS antenna module.

[rainier]

First very important determination: Does this occur with engine running or not ?

If it's fine with the engine off - your ignition system is interfering (it can create harmonics all the way to the 1.5Ghz the GPS signal is transmitted on).

Look for "elms fires" Run the engine at night in the dark with cowlings off - look for the typical bluish glow or spark discharges around the ignition system and cables.
The issue can also be inside the ignition module - some CDI systems are prone to this - that is an early sign of it failing.

[JimJab]

First very important determination: Does this occur with engine running or not ?

If it's fine with the engine off - your ignition system is interfering (it can create harmonics all the way to the 1.5Ghz the GPS signal is transmitted on).

Look for "elms fires" Run the engine at night in the dark with cowlings off - look for the typical bluish glow or spark discharges around the ignition system and cables.
The issue can also be inside the ignition module - some CDI systems are prone to this - that is an early sign of it failing.

Thanks Rainier, this may well be the cause, the EFIS/GPS became unstable at the very same time I change my RDAC RPM signal from the ignition coil wire to the Hall Effect sensor.

I did leave the wire from the ignition coil to the RDAC RPM coiled and tapped up in the engine bay, just in case the Hall Effect sensor did not work as well as I hoped and I needed to change the RDAC RPM back to this ignition wire.

It does seem strange on that very first test flight of the Hall Effect sensor, the GPS started playing up as soon as I was airborne and has always been so stable before this.

I will have a chance late next week to checkout the EFIS without the engine going and will have a look at night with the engine running. I might even change the RDAC RPM back to the ignition wire and see if the EFIS/GPS becomes stable again in flight.

After what you have said Rainier, I am now wondering if this ignition wire coiled up is acting like an antenna, it would only be about 30 cm through the fiberglass to the antenna of the EFIS/GPS that is playing up.

Also working so close in and round the HT leads when mounting the sensor, maybe I have upset one of the connection into the distributor cap.

Thanks Rainier for your help and to sparxfly for your time and help as well, I will do some testing and get back to you all.

Cheers
JimJab

[JimJab]

First very important determination: Does this occur with engine running or not ?

If it's fine with the engine off - your ignition system is interfering (it can create harmonics all the way to the 1.5Ghz the GPS signal is transmitted on).

Look for "elms fires" Run the engine at night in the dark with cowlings off - look for the typical bluish glow or spark discharges around the ignition system and cables.
The issue can also be inside the ignition module - some CDI systems are prone to this - that is an early sign of it failing.

OK, following up on this EFIS GPS issue.

I took the plane out of the hangar pugged in auxiliary power and turned on both voyager EFISs. Both EFIS got GPS fixes, so I brought up the GPS satellite page by pushing the "Shift" + "GPS" button. On this screen you could see 6-7 green satellite bar signals and 2-3 red satellite bar signals and all was stable.

I ran both EFIS without the engine for about 20-25 mins in the afternoon sun, temp was around 25c, so the plane would be hot inside, I had no dropouts of the GPS over this time period.

So then started the engine and ran that for about 10 minutes at different rpm settings trying to induce electrical interference or vibration, nothing caused the GPS to dropout. But I am not 100% sure that I have proven it's not electrical or ignition interference as I was not totally comfortable ground running the engine at cruise rpm for any length of time.

So with the engine off and the EFISs still on, I put my hand up behind the instrument panel to recheck the antenna lead connector to the EFIS for tightness, check my flatten coil of extra antenna cable was still in its position away from all other bus cabling and checked the antenna cable where it goes through the top of the instrument panel mount. My GPS antennas are velcro into the channel that runs around on the inside, just below the windscreen.

As I was checking the antenna cabling, I found as I moved the cable around or touched it with my hand in some places, I found I could increase or decrease the satellite signal bar strength, say by 5-10%, so I moved the antenna cable for better signal strength. But the GPS signal never drop right out as I moved the antenna cable around.

So back into the air I went with the GPS satellite page up on the EFIS, all was good for the first few minutes of the flight, then the I heard "GPS not available" and then a few seconds later "GPS available". The EFIS GPS satellite page dropped all satellite information as the EFIS announced "GPS not available" and remained blank of any GPS details even after the EFIS announced "GPS available".

It seemed the EFIS GPS satellite page does not refresh from the satellite dropout. So I closed the EFIS GPS satellite page and reopened it and the satellite information was back. The remained of the flight, 10 minutes so, had no further GPS drop outs.

I am wondering if the antenna has an issue, more testing.

Cheers
JimJab

[rainier]

You have mounted the antenna on a piece of metal to act as ground plane ?
This is required - if this is not done the antenna is much less effective and not a match - that causes the cable to go "live" and it becomes part of the antenna.

[JimJab]

You have mounted the antenna on a piece of metal to act as ground plane ?
This is required - if this is not done the antenna is much less effective and not a match - that causes the cable to go "live" and it becomes part of the antenna.

Thanks Rainier, as far as I can see, neither of my GPS antenna have been mounted with any type of ground plane, unless of cause the owner/builder was very smart and glued some foil on top of the Instrument panel housing and under the blue upholstery?

Both the Voyage GPS have worked very solid until just the other day when the pilot side started to become flakey and started randomly dropping out and coming back with in a few seconds. Some further information, the 2 GPS antennas are about 450 mm apart.

I have attached a pic of the Jab Instrument panel mounting and put a blue X and ring where I could attached some self adhesive foil to the bottom side of the instrument panel housing where the GPS antennas sits on the topside of the fiberglass housing.

Would a piece of self-adhesive copper or aluminum foil be ok for a ground plane, as it would not be grounded to anything?

Also I need to consider what could happen if the self-adhesive fails and foil drops off, is it remotely possible that it could end up in my electrical wiring behind the panel and short something out in flight.

JimJab

Showing area for tin foil

Tin Foil Ground Plate.jpg (80.77 KiB) Viewed 37283 times

[JimJab]

Further to my GPS issue.

Yesterday, I pulled my Voyager EFIS that had the GPS problem.

I did quite a bit of testing with the plane on the ground, with and without the engine running. I could not get the GPS to play up on the ground at all. It was only in flight it would randomly stop working for a second or two.

This made me feel the fault was being caused through vibration, so it could be a dry joint, broken wire or a cable connection that needed reseating.

After opening up the EFIS , I could see there was an AWM 20624 0.5/20pin/20cm ribbon cable running from the GPS board to the main board and there was quite a tight radius bend in this ribbon cable. So I took the ribbon cable out and using a small LED touch to shine a light through the ribbon cable I could see where a possible break in one of the ribbons conductors was on this bend.

So, I flexed this ribbon cable a bit to make the break look worst under the light and then put the ribbon back into the EFIS and on powering up the EFIS, the GPS did not work and a Code 1 fault was reported.

Not having a replacement ribbon cable on hand, I decided to replace the GPS cable with the one that connected the Camera Board to the main board.

On powering up the EFIS, the GPS fired into life and then found a full compliment of satellites.

I am quietly confident this ribbon cable was causing the problem, but until the EFIS is back in the plane with a new ribbon cable and it's then back in the air, you can't be 100% sure.

Cheers
JimJab