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Random avionics internals

AOA sensor teardown

Some of you may be aware of AvE. His videos are pretty entertaining on home workshop and general engineering discussions.

One of his viewers sent him a scrap AOA sensor from a herc. Interesting and entertaining. His surprise about the content of some of the internal components of “aviation grade” electronics may be familiar.



Inside an Ameri-King altitude encoder (AK-350). Date code on the ICL7109 ADC looks like 1998, week 40.

Construction (2 layer PCB, all through hole) seems similar to early 80s microcomputers like the Sinclair Spectrum.

Inside a Garmin GTX320 mode C transponder of late 90s vintage (mechanical rotary knobs on the front)

Solder side of the 2 layer PCB:

Component side – most stuff is SMD apart from the large electrolytic caps.

Inside one of the screened boxes (the PCB traces are likely filters, once you start getting into the GHz range it becomes a practical way of making them)

Inside the screened box with the TCXO:

View of component side with the boxes open:

Andreas IOM

Nice.

The encoder probably uses the EPROM / PROM to convert the 7-segment data from the 7109 to gray code.

Don’t you just love RF stuff? Probably anybody who knows this today has a beard (I don’t mean a hipster one; they are mandatory now) and wears sandals

I posted the innards of the encoder previously but they are all the same inside; I reckon they all just ripped off each others’ designs.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

Don’t you just love RF stuff? Probably anybody who knows this today has a beard (I don’t mean a hipster one; they are mandatory now) and wears sandals

Or is Chinese. Don’t underestimate them – see some of the teardowns of things like spectrum analyzers that are coming from China now (where low cost = around 3k, rather than 25k you’d expect to pay with something from Agilent)

Andreas IOM

Sure; they prob99 just copied the American stuff from the 1960s and 1970s. Fancy RF construction like that is very labour-intensive but they can do it for peanuts.

Agilent/HP have the problem that they can’t drop the price from 25k to 3k even if they could.

Administrator
Shoreham EGKA, United Kingdom

Well, there’s also that Huawei are the only manufacturer of 5G equipment that’s really 5G and outperform by orders of magnitude the stuff from Nokia, Ericsson etc. and that’s why there’s this controversy at the moment, because if you want to make a worthwhile 5G network there’s only one game in town for the stuff in the cellular towers, and why the UK government wants to set aside with as little fuss as possible any alleged security problems with Huawei. The Chinese are just three leagues ahead in terms of technical superiority with this stuff at the moment.

Last Edited by alioth at 02 May 09:35
Andreas IOM

Many people closer to the subject would differ

One view is that their software is crap. If Huawei is anything like the “higher end Chinese” routers e.g. Draytek, they are full of bugs and back doors – in fact exactly what the GCHQ has reported. They leave “factory” passwords in, etc. For example the older Draytek routers whose port 443 had a password of “drayteker” and unchecking the “remote admin” box didn’t disable remote admin; the only solution was to forward port 443 to an internal IP on which nothing was (hopefully) listening A back door? More like a front door.

Administrator
Shoreham EGKA, United Kingdom

Not all Chinese companies are equal, some of them are putting out some really decent stuff now (even if there’s a lot of crap still being produced). We also used to underestimate the Japanese, too. If Cisco, Juniper et al. rest on their laurels, they might have a problem within 10 years.

Last Edited by alioth at 02 May 11:28
Andreas IOM

Just watched the AoA sensor teardown; thanks for posting it @Off_Field.

They could certainly have made the position encoder more robust (avoided the slip rings) but apart from that the construction is probably really standard.

There is a lot more electronics involved in getting the AoA value. That resolver has to be energised and the output from it has to be demodulated. There is probably a whole PCB full of bits somewhere, and if that stops working, you lose the AoA function.

Not all Chinese companies are equal, some of them are putting out some really decent stuff now (even if there’s a lot of crap still being produced). We also used to underestimate the Japanese, too. If Cisco, Juniper et al. rest on their laurels, they might have a problem within 10 years.

Cisco have their own big problems with having got way too big. And there is a massive difference in culture and attitude between the Chinese and the Japanese. The Chinese seem to be trying to get rich quick and to hell with anything else. I’ve been dealing with firms there for 20+ years. The Japanese are self critical and want to continually improve, and they have done this from within, whereas the cases where the Chinese don’t make crap is mostly where a Western (or other e.g. Samsung) company has sent a load of their own people to live out there in the factory – as with phones etc. Japan is declining because they have done too well and got rich like the rest of us A generalisation I know but I see no change over the 20 years. I am about to pull a product line out of China because of the frequency at which they suddenly vanish and we lose a load of tooling.

Administrator
Shoreham EGKA, United Kingdom

This is the Skyforce Skymap 2. This box was popular in the 1990s. Specification A colour version, the Skymap 3C, came later.

I bought one the day I passed the PPL skills test. It was about £500, just about usable for finding Le Touquet, but there wasn’t much else. With no keypad, waypoint entry was too painful but IIRC one could upload routes into it from Navbox.

I soon moved to tablets and proper moving maps and the Skymap ended up in the emergency bag, next to the life raft, and I put in new batteries every year… Eventually it was replaced with an ex Ebay Garmin 196 which I still have there.

Recently I picked up another Skymap 2 out of a dustbin in some avionics shop. Here are the internals. It was a tour de force of design back then, 25 years ago…

The monochrome LCD is an off the shelf item from Japan

Main processor board. The 68331 is still manufactured, amazingly

The back of the processor board, with 128k x 16 SRAM. The extra PCB is the GPS module

GPS module. XCS38140 is an unknown part, existing only with some old stock outlets, but I assume it is a processor because of the 128k x 8 Flash chip next to it

Back of the GPS module PCB. The huge chip is another 68331!

Honeywell later bought Skyforce and they did work on the KLN89, KLN94, the KMD150 (a panel mounted “certified” version of the Skymap 3C), and the KMD550 / 850 MFD of which many thousands were sold.

Administrator
Shoreham EGKA, United Kingdom
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