The MFA (that's a little 1980s on board computer) in my Golf has packed up, after a battery charger was connected the wrong way round to a flat battery. I'm currently getting the clocks to bits to look at it, but is there a reasonable hope of finding the bit that's gone kaput? Where should I be starting?
If you're really lucky it will be a diode.
However it won't be and you will have fried the processor. Sorry about that.
Look for anything that looks like it got hot (scorch marks on PCB, paint or plastic covering component discoloured.)
In reality you should be starting at a breakers. Mind you, if it were mine I'd pull it apart in the blind hope there was a fuse on board.
Stupid Boy
Shit, I didn't know we had anyone *that* hopeful left..... lol
Stupid old bloke more like. It was my Dad what did it. Without his glasses on.
Am I right in thinking that diodes only stop current up to a certain point? We obviously wouldn't be talking huge voltages, but we are talking BFO charger capable of chucking out a good 300 amps or so...
I would have what seem to be the rarest clocks in existence. 140mph Motometers, whereas everyone seems to have VDO clocks. Oh well. I've managed to mark the face of the rev counter, but the speedo's a seperate item, so I can always buy a working set and swap the rev counter / MFA unit round.
Doki ("Doki" ) gurgled happily, sounding much like they were saying:
The magic smoke escaped, eh?
Yeah - infinity unless you're unlucky enough to weld both halves together.
Irrelevent as the gauge of wire going into the connectors of the MFA can't carry that much or anywhere near.
snipped-for-privacy@burnt.org.uk wrote in news: snipped-for-privacy@4ax.com:
Well, before looking at the controller for the display, first identify its power source. Does it feed 12V directly from the battery or is there a separate 12V to 5V PSU to feed a number of peripherals?
A separate voltage regulator would be fairly easy to build/source.
If the PCB uses the raw battery voltage then it will need some voltage regulation circuitry. This will be where the problem lies, most likely. The fuse/diode that burnt mentions or a voltage regulator IC (the ones from the
1980s often look like a 3 pin transistor) are favourite culprits. With a bit of luck any components will be generic rather than proprietary.
Go and finish that half empty glass.
They act as would a mechanical valve. The current is allowed to pass in one direction only - not the other, unless the voltage rating of the device is exceeded. It is also possible to destroy the device if too much current is passed through it or if its voltage rating is exceeded in its reverse direction. A good one, passing a current in its forward direction will have a voltage of 0.6 to 0.7 across it.
They can be used two ways to prevent damage from a reverse polarity connection...
Personally, I would not expect there to be any such reverse polarity protection to be fitted.
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