| Electronics > Repair |
| Help Identifying Vintage Component |
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| T3sl4co1l:
--- Quote from: fzabkar on May 22, 2023, 04:48:27 am --- --- Quote from: floobydust on May 22, 2023, 04:38:32 am ---Logo "H" OK I found the manufacturer is Hilton Capacitor... --- End quote --- https://web.archive.org/web/20050210214206/http://www.tantalum-pellet.com/ --- End quote --- Wow, looks like a 50s era photo; and the other identical but for air-brushing out the identifier (presumably after being bought out), didn't even bother to photograph new parts, haha. Nicely spotted! Tim |
| Drjaymz:
Wow, I would say that these are exactly what they are. So we know its a capacitor. Picture attached. The board is a fibre board, hand twisted blobs soldered and epoxied on - which looks a lot like 60's era stuff. I can't easily remove the fibre board because the tiny relay windings are bonded to it at the bottom and I don't want to break it, especially as it now works. I warmed up the solder and removed the cap with tweezers and any replacement will probably go on the outside. I have traced out the diagram and will post that a little later. The capacitor goes between the blue wire (ground) and the top most blob in parallel with a 6.2k resistor. That then goes down the 20 degree slopey bit to the trimmer. And that junction has an 11.1V zener that pops out below the trimmer and goes across to the transistor base (which you can see). So that capacitor does see considerably more than 15V. In fact we have to see > ~ 12V before the base lifts above zero at all. At the end of the day, its just a ripple filter for something that shouldn't ever activate so its value isn't that important. What's important is that it isn't open or short and has some capacitance probably in the 10 -> 100uF region. I'll draw up the schematic in a translatable form because my mistake was drawing it as a standard 12V top 0V bottom schematic which confused the hell out of me. It also latches once triggered and I couldn't work out how it did that last night but maybe will have better luck today. Now I know they are caps that makes tracing it a little easier because when you're reverse engineering you tend to draw what makes sense rather than what you actually see. BTW there is another tant filtering the RHS and I tried to measure that my disconnecting one end and it has no capacitance whatsoever, couldn't get it to read on my meter, so its either duff or something really low like a few pf. But if you think about it they probably should be in the uF range given the time constant, because the relay isn't going to respond at khz or Mhz anyway its going to trigger or hunt in the hz region - which is my reasoning. So quick summary of what this is meant to do, in an aircraft alternator excitation is switchable, and because of some incident probably in the 1930s they decided they don't trust the regulator to regulate and so for safety they measure the bus voltage and if it exceeds 16V then the excitation is cut off completely. Because in flight the engine is 75% full power if the excitation fails at full then the alternator wants to produce ~ 300V and quickly becomes an issue because the batteries are lightweight i.e. 35Ah or less. That and the satnav costs 15k and any instrument that fails is probably 10k. You'd think if you bought a modern cirrus for £1 Million that it would be more sophisticated, but thats not how aviation works. No, we still have mixture control and magnetos. |
| fzabkar:
Something like this? |
| Drjaymz:
--- Quote from: fzabkar on May 22, 2023, 07:51:06 am ---Something like this? --- End quote --- That is just the regulator. I can see it uses the zener reference to control the field current (I say control I think its on or off). So if you look at my attachment this circuit is in the regulator part. Its more or less the same as that internally. It actually has a neon indicator used as a TVS device which is quite neat, and there is one capacitor between the zener and ground. In the actual aircraft that capacitor is also toast and thats the reason the ammeter bounces up and down. I do actually have a new (June 2022) certified part for the regulator. But I wanted to check the OV relay actually worked on the bench and I subsequently found out that it didn't! |
| Haenk:
Some serious measures have been take to ensure the trimmer is not re-adjusting itself. Ever. :-+ |
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