We have had strange things happening since we fitted the repaired magneto a few weeks ago.
First, radio reception has degraded quite a bit. Never had a problem before we removed and repaired the magneto.
The next mishap was two days ago when my pilot friend flew my aircraft from Italy to Hannover when a couple of hours into the flight both Avidynes and the ADL went black. No CB popped. He recycled the avionics master which momentarily switched off everything and created some stress with ATC.
A few minutes after both Avidynes and the ADL went black again so this time he left the autopilot off as it had commanded an unexpected climb and he thought this could be the offending equipment. By chance the radio remained on for the remainder of the flight.
On the ground he ran everything again with no issues. He pulled all CB to reset them and then flew to my IA the next day(todax). No problems during the entire flight and my IA could not find anything. A few hours later my friend took off again to come and pick me up in Italy. Unfortunately, on this flight both radios and the ADL went pouff again so this time he did not cycle the avionics master but just the boxes themselves. They went black again almost immediately. This time he pulled the CB of the ADL and the one for the Stormscope (strangely, this one also kills the ADL) and now the Avidynes stayed on for the remaining 2 hours.
The Avidynes are on BUS1 and the ADL is on BUS3, we can’t figure out what makes these three boxes go black at the same time. No CBs popp. We also don’t understand why the ADL is connected to two CBs, is this normal?
Everything started with the magneto repair and we can’t figure out how this could be connected. We are at a loss. I posted this on the Socata site but there is a deafening silence. I suspect support there is directly correlated to the amount “donated”. I hope to have more luck/help here from the electrically savvy forumites.
Thanks
Placido
I am sure people with much more experience will comment but my first reaction would be look at the connections on buses (and everywhere) to the negative side of the battery. These could possibly be shared with lots of devices. Was a strap dislodged somewhere close to the Magneto?
Anyway others will have much better ideas!
I flew home today from Italy and while the radios worked until we landed it was quickly apparent that something is not good in the electrical system. We took off with the ADL CB deactivated as it was the only other instrument going black together with the Avidynes but it is not on the same bus.
I saw a number of flickerings. The Insight G3 screen flickered and the amperemeter also had very short drops of current. The ALT light came on for a millisecond also once or twice but not everytime the G3 flickered. I turned the Nav lights and the Pitot off to shed some load and then the flickering seemed to stop.
Maybe the Avidynes and the ADL are more sensitive to current drops and just switch off while the rest is more tolerant. I have no clue what to look at.
I am in dire need of some pointers.
Thanks
Placido
AFAIU the magnetos need to be grounded, but not as most other stuff but to a special part on the engine. But I really don’t understand much of this either. I would have the mounting and connections of the changed magneto checked by a third party who knows what they’re doing.
On a little similar note, we have an old Jodel where you can hear some radio interference from the mags at certain power settings. Since it has no other electrical system than the battery powered radio, it’s not really an issue.
Don’t know if this helps.
Have you tried running on one magneto briefly when the issues occur (the one not changed, at lower power settings)?
There is something very strange going on but it is likely to be something simple for it to affect so much stuff.
Starting with the most basic, can any of it be reproduced on the ground, possibly with a 28V ground power unit, after the power is on for some time, hopefully with cruise loads on? If so, you will find it soon enough. The ADL box is just one box that contains the Iridium modem. It can’t possibly be powered from two buses at the same time, can it?? Maybe @Sebastian_G might know. If you get access to the back of the circuit breaker panel (just a few screws) then you can see what is going on behind there. Maybe some wires have come off; the CBs can get hot especially if some terminals have not been properly tightened and heat up.
It could be a problem on the PCB which carries the 3 or 4 avionics bus relays. There is (on some TB versions) a relay which is activated when you start the engine and this relay’s normally-closed contact feeds power to the three avionics bus relays. The idea is to disconnect power to the avionics during engine start, to protect it from starter motor induced spikes (cars have the same setup, or used to). If this relay is duff or intermittent, you could see all kinds of avionics bus issues. I think that PCB is at the base of the centre stack, but I am not sure. If you need any 28V relays, I have a load in stock 
You need the wiring diagrams (I have the Feb 2006 TB20/21 MM with various composite diagrams) and somebody who is happy to get down there and get his hands dirty.
The magneto interference is likely a separate issue. Maybe one of the capacitors (condensers) is duff.
I have the ADL with the screen which is built into the aircraft. It is connected to the Avidyne as it takes the FP from it.
There is a CB that just switches off the ADL and then there is another CB that switches off both the ADL and the G3. This in itself seems a bit strange to me but then I have no electronics idea.
The relay you are referencing is this the battery solenoid the guy over at Socata.org mentioned. What does PCB stand for?
Thanks
Placido
It looks like somebody wired a CB off another CB… not the way it should normally be done. All CBs for a given bus should come directly off that bus. Whoever did that should be shot.
The relay PCB (printed circuit board) I am thinking of is this.
To eliminate more basic possibilities, what is the bus voltage showing during cruise? It should be 28.0V. If that is ok, the upstream stuff like the ground power relay and the battery relay are not the problem.
Europe has a dire shortage of competent avionics people especially ones who will work freelance on a per-hour basis and understand electronics, rather than just follow wires.
The wire to our “starter engaged warning light” was disconnected, taped out of the way, but forgotten when work was completed. You look outside when starting, then check warning light is out – and fail to notice it was never on.
Months later, the wire came loose, and whipped about in the inside-cowling airstream. Each time it earthed, the oil pressure indication went down. We changed the sender, with no improvement, before spotting the cause.
Might a loose wire, not connected to the suspect systems, cause odd effects?
PS Not a professionally maintained aircraft – we’ve only ourselves to blame. And only radio, Mode S and gauges on electrics.
Peter, the ampermeter was in the green but below 28. When I shed the Pitot and Nav lights then it went to 27.2
During the flickering the amperemeter showed a short drop of power to the yellow level but just momentarily. The ALT annunciator light also came on for a millisecond so it looks we have some sort of fluctuation.
You will need to get somebody to take a look at the plane.
There is a slight chance that a visual inspection will reveal something but since the stuff basically all works, probably not.
You will need to replicate at least some of the issue on the ground. It is almost impossible to debug during flight. In extreme cases one can attach wires to various points and measure voltages in flight.
An ampermeter (ammeter) shows current, not voltage. Do you have just the edge gauges (which have no numbers on them; just coloured bands) or is there a digital voltmeter too?
If the bus voltage with engine running at say 1500rpm is low, say 26V, then you need to look at the alternator and the voltage regulator. It is possible that the rectifier on the alternator is faulty and together with a bad battery connection this could be putting a lot of ripple on the bus(es) which could cause some avionics to drop out.
