Any 'lectronics gurus, purveyors of the magic string here?

[Pete.]

I've got a small device that has blown a component that I'd like to get repaired. It's an add-on box for a datalogging unit, it houses several small sensors (MAP sensor, acellerometer etc). It can be powered by a 12V supply as a standalone unit, OR by a DIN lead from the datalogger itself. When it's powered from the datalogger by the patch lead, the unit works, I can program it via serial lead with the software and it communicates well - but the on-board sensors don't work.

When I power it by the 12V and GND terminal it stays dead, though the relay clicks.

My suspicion is that it's been fed 12V down the 5v output (provided as a regulated supply for powering external sensors).
Here's the unit:

[Pete.]

And this relay clicks but doesn't power the unit. You can see there is a small burn mark next to the diode.

I'm told that the voltage regulator next to the relay might be fried so I put a pic of that too.
Anyone in the UK here who can test this thing for me and perhaps replace whatever I need to make it power up? I'm not fussed about the built-in sensors if they are all toast, though it would be nice if they weren't - I want to be able to connect external stuff to the 0-5V inputs and use it with my newer datalogger (which uses a serial protocol to connect, doesn't power the unit).

[John Rudd]

I've done some smd rework in my time....

PM me if you want to discuss further on a repair..

[Troutsqueezer]

A schematic and a multi-meter are the two handiest things you can have right now. The circuit doesn't look complicated and a few continuity checks will probably reveal the problem. The voltage regulator is a common variety with pin 1 to ground, pin 2 the output and pin 3 input.  Following the 12V input traces along and doing some easy diode checking and short checking along with a voltage measurement here and there will probably be all that is needed.

[Pete.]

Thanks for the replies. Troutsqueezer, I  ran my meter over it (very tentatively) then jumped some power from the 12V rail to the input pin of the voltage regulator, and it all came alive, so it looks like a simple duff relay. A local guy I know from another forum has offered to swap it out if I get hold of a replacement, so it does look like I have it sorted now.

Thanks again.

[trevoratxtal]

Thanks for the replies. Troutsqueezer, I  ran my meter over it (very tentatively) then jumped some power from the 12V rail to the input pin of the voltage regulator, and it all came alive, so it looks like a simple duff relay. A local guy I know from another forum has offered to swap it out if I get hold of a replacement, so it does look like I have it sorted now.

Thanks again.

That type of relay are noted for sticking, a sharp tap often frees it up for a while.
So if you suspect a relay give it a flick or tap it could give you a clue.
Trev