The silent GPS

As a part of my work, I recently had to work on a GPS unit. This is about my misadventures trying to get it to work.
The trouble began with it being a rather old unit, and as such it wasn't exactly as simple as more modern units would have been. Still, I did figure out how it was supposed to work - so far, so good. I got the components, set everything up, and expected to get a reading.
Except I got no such thing.
My immediate first guess was a communication problem - I wasn't too familiar with it after all and the power light was on. So I looked it up, and checked the cable. Nope. It's working perfectly. I checked the settings against the manual. My settings were correct.
Then I went through the manual again to see whether any of my commands or settings were wrong. Nope.
The only other option was power. On closer inspection, the unit wasn't drawing any current. So, I had identified the problem.
The unit had a fuse. That was my first suspect. Tested it - no, it wasn't blown.
Then I checked the power circuit. It said 12 V, but the GPS itself was rated to handle a range of voltages, so to be on the safe side I had gone with 11.5 V. On closer inspection I saw a 7810 regulator. The rated input is 12.5 V, but even with a lower voltage it should have given a steady DC output, though probably at less than 10 V. The GPS should have worked under those circumstances. still, nothing had worked and I was a little short of resorting to an exorcism, so I thought I might as well increase the voltage to 12.5 V. Still, no response. It simply wasn't drawing any current.
At this point, I was reaching the concluded that something was possibly fried.
The next task was identifying what was fried. It was either the power supply or the GPS. Fortunately the designers of the unit had allowed for measuring the current output. That allowed me to determine that the output power from the supply was zero.
Having determined that, I checked the supply again. Possibly there was something I had missed, something that would allow me to identify the real problem. Perhaps a small switch on the board...
There was no such thing. Finally, I closed the box, and lo and behold, on the outside of it, was a rather large power switch. It was in the off position.
I turned it on, and well, it worked.
At least, thanks to this fiasco, I had read the manual thoroughly and all the connections were right when I finally switched it on. On the flip side, I wasted quite a few hours of my life.
So, the point I want to make is, always check the obvious, and do not blindly trust power buttons.


yours truly,
Falcon-15-X-C