Canon 300D, dismantling and fuse repair

This page is about replacing the fuse which often blows on the Canon 300D. The problem persists with later models, even up to the Canon 450D. I'm a wedding photographer, using mainly Canon 5D (which I've made attachments for but not yet had to repair) but I often carry one of these older cameras as well, with a long, long lens, for informal "candid" shots at the reception.They're good fillers for albums, particularly as monochromes.
 I've also made an attachment which allows me to mount and fire two Canon 300ds simultaneously, the second one with a really slow shutter speed. If you pan right, you get the horse and rider sharp and the background beautifully blurred (while the first camera gets the sharp, standard shot). If you pan wrong... everything's blurred. Something like a 1/25 of a second works for a horse on a cross country course. Follow this link and, somewhere in the slideshow, is Zara Phillips at speed, at Burgley horse trials last year, with pretty good background blur.
Anyway...fuses. I've recently been helping someone who, because of complicated time constraints elected to dismantle his 450D which had gone dead, rather than send it back. Apparently the internals are different (not surprisingly) but the fuse is still identifiable, and still draws the same amount of current...and still blows. This chap (in Spain) managed to replace it with information from these pages, got his camera working again, and was able to take it on holiday.

Remember though, that any tinkering like this will invalidate your guarantee. Here's the email (reproduced with his permission) of one happy guy:

Hi Mike !!
 
Just wanted to let you know that I fixed my friend's 450D, and it was a blown little fuse, as suspected.
 
I did not take any pictures of the surgery because we were in a hurry (he just went on vacation). Don't worry because he went away with a simple short instead of the fuse (I didn't have anything to replace it with) and we will do a "proper" repair when he gets back (and I get something that behaves more like a fuse...). He won't use the suspicious CF card and that's all. When we put a fuse in place, I will take the pictures and let you know.
 
The disassembly was a bit different from the 350D and the current flowing thru the fuse is about 180mA with the camera on, similar to what you describe. The PCB was (obviously) different but the fuse was easy to locate and looked similar to the ones in your 350D's pictures. Looking at the traces, it seems to be in the same (electrical) place than the one that blown on your 350D.
 
I will get back to you when I get the pictures.
 
This fix wouldn't have been tried without seeing your web pages, so a big THANK YOU goes to you from us.
 
Regards,
Roberto

So..back to my own story, last year, with a 300D which just stopped working; no power, no lights, no screen, nothing. 

It happened immediately after replacement of the memory card, which had been acting strangely in the card reader; not transfering pictures properly. That was actually a bit of a clue, although I didn't realise it at the time. The same memory card was then plugged into a brand new Canon 350D which also died. At that point I twigged, and threw the memory card away. So the moral here is: if the CF card even starts to act up, put it in the round file before it damages something much more expensive than itself.  

A web search indicated that there is a fuse which can blow on the circuit board immediately below the mode dial. This page is about replacing the fuse. If you were looking for other Canon 300D and 350D camera repairs, then click here to get to my Canon repair menu page. I also use a Canon 5D for weddings, but I haven't had to fix it yet...

Back to the dead Canon 300D. The guy who posted this had actually found out the hard way; he'd dismantled the camera to replace a broken mirror pin (a common failure on early 300Ds) and had thought that because the camera power switch was in the "off" position, that there was no need to take the battery out.

Wrong! The power switch is more of a "software switch" on these cameras. Lots of things are still powered up even when its switched off, so take the battery out before you start dismantling it. Also take out the little backup battery (down the side of the main casing).
  
Start by peeling off the little plastic cover over the screw on the rear cover. Then find a screwdriver that really fits (ie: it goes in without rocking) and remove all the external screws. The cocktail stick is to point at the screw; it won't undo them.
Unclip the battery compartment door by pushing that little pin upwards.
Then you can get at the screws to remove the hinge bracket.
There are two rather well hidden screws down here. You can only reach them after you've got the front casing off, by sliding a screwdriver in through a slot in the metalwork. I left the one nearest the cocktail stick out altogether when I re-assembled the camera.

 
Important point number two (which I found out the hard way); the big capacitor on the opposite end of the body to the battery pack (the black cylinder in the picture above) has 200 plus volts on it. It's the power source for the flash, and it hurts if you touch it! You need to unsolder the five wires shown in the picture in order to remove the top casing of the camera. The thicker, blue and white wires, are connected to this capacitor. If you leave the camera with the battery out, the charge will eventually leak away, but I've no feel for how long this would take...might be weeks. I discharged it myself, carefully, using a 5k ohm resistor with a couple of leads attached. The smaller the resistor, the faster it discharges. With 5k it takes a couple of minutes.
When you've removed the upper casing, unsoldered the metal cover off the circuit board and got down to the fuse, (tiny surface mount square thing) you need a multimeter to see if there is continuity across it. When you've established that it's blown, you can do one of two things: you can link across it (use the spare pads next to the fuse) or you can replace it. I chose to replace it, on the basis that "it's happened once, it might happen again."

The fuse is small, tiny, microscopic, about 2mm square. It's at about 9.00 o'clock relative to the big square thing just right of centre in the picture, and you can see the link I've soldered in just above it. There's no rating on it, and it's smaller than the smallest surface mount fuse I could find from RS. So I linked in an ammeter, put the camera together again, switched on and measured the current draw. It's about 100-150 mA.
The next up standard size of miniature surface mount fuse is 250 mA, so I used one of those. It's too big to fit under the metal shield that's round this circuit board, but there is room outside, so I soldered a couple of wires onto the spare fuse pads, lead them outside the metal shield, attached the fuse and encased the whole lot in red heatshrink.
It works a treat and the covers still fit back on the camera.
  

Note, finally, that there are two other fuses on this circuit board. I've not heard of any instances of them blowing, but if the central one is intact, you could check across them as well. And, if you do discover that one of them is blown, please send me an email mike@michaeljdixon.co.uk  with any symptoms, etc of the failure and I'll add it to this page. (It may be that with one of the other fuses blown, some things work and others don't).

Footnote: this repaired camera has now been in use for several months, with a range of lenses, and with the flash on. The replacement fuse has not blown, so my current draw measurement can't have been far out: I had wondered whether big lenses with more powerful AF motors might have pulled more amps. But it's fine.  
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