I got an Eos 20D in a job lot of Canon gear and while it seems to work there's an annoying problem - if the flash is needed it pops up but the camera seems to think it hasn't; it clicks three times then gives an error 05. I'm guessing that there's a sensor or switch somewhere that has gone wrong. I've tried blowing compressed air around the hinges etc. in case it's something there but it hasn't helped. I really don't want to try to fix anything more complicated, with my luck I know that it will end with a dead camera, and I know that a pro repair will cost much more than it's worth... Is there anything I can try short of going inside the casing? I have no problems with selling it as faulty, but I would be happier if there was a fix. One thought I've had is to sell it with a flash - is there a basic Canon or compatible model that will do the job?
I definitely wouldn't open the casing, the camera is 14 years old and worth only a modest price anyway. The flash really won't affect the price much. You could pair it with any manual flash if you like. It supports the ETTL flashes so maybe find a 430 EX for a deal and pair them as a bundle if you want to sell. I guess I never really thought selling my 20d was worth the amount id get at this point but I suppose it is better than collecting dust.
I got it very cheaply, as part of a deal with some other cameras and lenses, but I really have no use for it - it's not even a good spare for me since it uses different batteries to my 400D and I take a lot of flash pictures. Selling it on is the best option, but as you say it's not worth spending a lot to get it to full working order. I don't see many Canon flashes but I do usually have some generic flashes around, I'll include one when I sell it.
This probably will not help but I had a 20D and the flash would not work if there was a hotshoe cover present. Removing it enabled the flash to fire. No idea why this is but if you have a hotshoe cover on it, you could try removing it.
Yes, I've had that happen when I tried one of those spirit level gadgets, but in that case the flash didn't open at all, the camera seems to think that there's a flash in the shoe. This is a different problem, the flash is opening but the camera doesn't seem to know. I think that using an external flash is the way to go, I'll just have to try to find one that actually works - not as easy as you might think, most of the flashes I pick up in job lots etc. are useless because the batteries have leaked badly enough to damage other components. Annoyingly I just gave a nice one away.
Definitely - the first thing I did when I realised there was a problem was check if there was something in the shoe etc. stopping the flash from opening fully. Unfortunately that isn't the problem, pretty sure it's a switch or sensor fault.