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Random avionics internals

You should post it. It is always interesting to see current stuff.

Shoreham EGKA, United Kingdom

OK, I am just too curious to not look “inside” stuff but this electronic stuff all look like personal computer internals to me.

This is the MGL iEFIS Explorer Lite. The “lite” is the all in one package

Here is the electronic circuit breakers.

Then the ASX-1, my “backup” alt and ASI (in case the EFIS goes black, but still need battery). This one actually looks a bit cool inside.


That stuff is well made. Nice and modern construction, nearly all SMT.

Thanks for posting that.

The MGL is not a PC; it appears to be all custom stuff.

The only negative comment I would make is on the inter-PCB connections which are often hard-soldered and suspectible to vibration. This is really clear on the last pic above. However it will be fine if the PCBs are well supported by the case of the instrument.

Shoreham EGKA, United Kingdom

Peter wrote:

That stuff is well made. Nice and modern construction, nearly all SMT.

Wouldn’t get near to passing the test specs for modern automotive electronics. To be fair it probably doesn’t need to.

Last Edited by Neil at 12 Aug 11:40
Darley Moor, Gamston (UK)

Wouldn’t get near to passing the test specs for modern automotive electronics

In what respect?

Shoreham EGKA, United Kingdom


The glideslope receiver

Shoreham EGKA, United Kingdom

Does anyone know what this is? I believe it came out of a TB10… The TO5 transistor is a 2N1711 with a 1985 datecode. The TO18 one is a good old BC108C The diode is a 12V zener.

I wonder if it is something to do with instrument backlight dimming? But the transistor cannot possibly be dissipating much power.

The construction is typical of Socata and some very low volume production in a wooden shed. The connector fingers are not even gold flashed…

Shoreham EGKA, United Kingdom

IIRC, just a WAG : That looks similar to an gear and/or stall audio warning board I pulled out of a CEssna retract – I think the pot was for volume control.

Last Edited by Michael at 12 Jan 08:24

Looks like it serves to switch something on (or off) when the supply voltage passes a certain threshold; the threshold being adjustable with the trimpot. Apparently meant to be more or less universal, it can cater for different kind of loads (lamp, relay, buzzer) – with an inductive load, an inverse diode is required to protect the 2N1711 and the place is neatly provided, but unoccupied here.

The lack of cooling to the 2N17711 tells us it is meant to switch, either ON or OFF, but I would then have expected some kind of schmitt trigger for improved stability – easy to add as two transistors are present. It is really a simple design, not to say primitive. And the kind of trimpot used – open, ready to be disturbed by the least bit of dirt and/or vibration – doesn’t promise a high degree of reliability/stability, either. In fact it is surprising to see this contraption coming out of a certified plane – who can ever have certified it?

The 12V zener seems to indicate a 24V installation, is that correct for a TB10? In a 12V application it would be 5,6V or so.

With reference to the upper picture, the connections are clearly (lower) ground, (middle) switched output, (upper) supply.

Last Edited by at 12 Jan 09:02
EBZH Kiewit, Belgium

I traced the circuit

The pot is currently set to about 200 ohms, so this is a threshold detector, whereby the 2N1711 is ON until the supply exceeds about 13V and then it turns OFF.

So, maybe an alternator fault detector in a 12V aircraft (whose bus voltage is 14V)?

It could even be a voltage regulator for an alternator but the 2N1711 could never carry the field current.

Yes – the use of an open pot in this application (humidity, vibration, etc) is really crap practice, but avionics is full of this sort of thing. Those Allen-Bradley ceramic-substrate pots were OK for a benign environment and were really popular in industrial electronics in the 1970s.

Shoreham EGKA, United Kingdom
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