A friend recently asked to me look at a piece of kit that had been giving her trouble. It was intermittent and a swift whack or fiddling with the connections would usually bring it back to life but it had gotten to the point where it was unusable so she had sent it to repair When it arrived back it was completely dead and not wanting to fork out even more money or be without the device for an extended period of time, asked me to have a look.
It's a mains powered device and since UK plugs have a cartridge fuse inside, this is always the first thing to check. Unfortunately the fuse was fine.
I opened the device, couldn't see anything obviously loose or damaged so started checking the continuity of the mains flex from the plug to the device. A-ha. Both the live and neutral were intermittent, so it was probably a break in the cable some place.
I cut the plug off, disconnected the flex from the equipment end, and replaced it. When I came to remove the plug from the old flex to attach to the new one, I found that both the live and neutral screws were really loose. What should have been a five minute repair took around an hour.
Always, always check the simple things first.
On the plus side, the equipment looks nicer with a new piece of black flex rather than the grubby original white one.