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400D XTI excessive power consumption

Hi camera hackers,

A few weeks ago, I bought a second hand Canon 400D XTI. This is its story. When I got it, there were several things broken, all of which I managed to fix so far, but one problem remains:

The camera draws 50 mA when switched off, which means that it completely drains a brand new, fully charged battery overnight.

I would like to ask you about your thoughts why that could be, and what I could try to narrow down the cause. Let me tell you the complete story of what I did so far, maybe some of it is relevant.

The camera was quite cheap, and the offer didn't mention that it was broken. As they say: If it sounds too good to be true, it probably is. But there you go. When I got it, I was kind of disappointed to notice that it didn't work, but also a bit excited. After all, it meant that I had a reason to open it! I guess this is the place where I don't have to explain why this got me excited and I why didn't want to send it back.

The camera came with a 18-55mm kit lens and an aftermarket battery. After I charged the battery, the first thing I noticed was that it had the infamous autofocus mirror lockup problem that most cameras of this series seem to exhibit after some time. Luckily this means that there are instructions out there on how to fix it [1]. The instructions I found were for the 300D, where the plastic pin responsible to fold up the second mirror is glued in place. The 400D doesn't use glue, instead the pin is just clipped in. It was snapped out, so after removing the case and the flash PCB, all I had to do was give it a little push so it snapped back into place. I'm pretty sure that had I known this before, it would have been possible to pull the pin back into place from inside the mirror chamber, without opening the case. Anyway, the autofocus mirror now folds up like it is supposed to.

The next problem was that the lens was not working at all. The camera displayed F00, just as if there isn't a lens attached, or an analog one that doesn't communicate with the camera. Time to open the lens! It appears that the previous owner dropped the camera, thereby breaking the lens. The plastic lens mount seems fractured and glued back together. Once screwed open, it revealed that the flat cable which connects the contact block to the main PCB was ripped apart. The cable is short and consists of 7 comparatively thick lines, so it was possible to solder in 7 short separate cables instead [2]. Now the lens works fine, with autofocus, aperture and all.

I went shooting happily but soon noticed that the camera sucks the battery dry in just a few hours, even when switched off. I glued two strips of aluminum foil to a strip of paper of the width of one of the battery contacts to measure the current [3]. Indeed, I measured about 40 to 50 mA when switched off. The current when the camera is turned on, with and without display, is okay according to the first column of the table in the service manual [4], p98. The table has a second column, however, which says "Actual Measurement" and whatever this means, the values I measured are roughly 40 mA higher.

I have two aftermarket batteries, the one that came with the camera and a new one. Both 750 mAh, 7.4 V. Both give the same measurements. I also connected a constant-voltage power supply directly to the camera's battery contacts, set to 7.5 V, and measured the same 50 mA.

When I opened the camera's case for the first time, a little plastic piece fell out [5]. I couldn't figure out where it came from, it looks like what perhaps could be a switch of some sort. It is however neither the switch for the CF hatch, nor the one for the battery hatch, nor the one detecting whether the flash is open. Those three are still intact.

Furthermore, the camera seems to have gotten wet once. The metal shields on the main PCB are a bit rusty [6], and so is the USB connector. There is also a bit of rust inside the foil that makes up the directional buttons and the "SET" button. All buttons and the USB work fine, though.

One of the connectors holding a flat cable on the main PCB showed signs of corrosion, it had some of the cyan kind of goo that comes from corroded copper [7]. I cleaned it with a toothbrush, didn't make a difference.

I tried to disconnect as many cables in the camera I could reach without unsoldering the metal shields, always measuring if power consumption changes. No effect: as long as the main PCB is connected to the battery PCB, it draws 50mA.

I did a firmware update from 1.1.0 to 1.1.1. No change.

It doesn't make a difference whether the lens is mounted or not.

That's as much as I can tell. I haven't yet disassembled the camera completely, in particular I didn't unsolder the shields to disassemble the main PCB yet. I only took away the case.

Do you guys have any thoughts or ideas what could be wrong? What can I do to narrow down the problem? How does water damage manifest itself? If I disassemble the camera further, what should I look out for?

Thanks in advance,

[1] . . .
[4] . . .

Tue, 15 Apr 2014 20:12:02 +0400

Wow, Markus, I never seen such a well written troubleshooting post in the past. First thing that comes to mind is an old battery, but you have already eliminated that. The flash has a battery draining circuit when flash is on. Maybe the cut off circuit is bad. Have you looked into the flash area and its capacitor?

Chieh Cheng
Wed, 16 Apr 2014 04:26:38 +0400


Here is an update on my camera. Short story: I couldn't figure out what's wrong. Long story: I opened the camera again, this time unsoldering all metal shields from the mainboard. I was told that these are probably for electro-magnetic fields, both from and to the outside world, so in principle the camera can run without them (good to know, just in case I wouldn't manage to reassemble them).

While unsoldering the right shield, I applied a bit too much force and ripped out a small part of the circuit board. The camera doesn't seem to care. On the photo it is visible as a square copper patch, to the right of the middle chip.

Underneath the middle shield are two ribbon cable connectors, both leading to the sensor unit directly below. I unplugged them, together with all other cables leading to the mainboard, and removed the mainboard. Without the mainboard power consumption dropped to zero.

I kept everything disconnected, but connected the power lead wire to the mainboard [1], and measured the dreaded 50 mA again. Everything else was disconnected. The autofocus unit, the flash unit, all the buttons on the back and top covers, everything. I also unplugged all the connectors I could reach that are between components other than the mainboard.

While taking the camera apart, I repeatedly measured power consumption, and strangely enough power consumption slightly rose the more components I disconnected. When the camera is put together, but switched off, it draws 40 mA. This value rose gradually to 50mA the more cables I disconnected.

There are similar metal shields on the front side of the mainboard, which I also removed. I was looking for water damage, because one of the metal shields on the back had a bit of rust on it, but on the board underneath everything looked fine.

I only partially resoldered the many connecting points of the metal shields, as this turned out to be even trickier than unsoldering them. The metal shields conduct a lot of heat away from the soldering tin, so it is hard to get the tin to melt.

I cleaned all the contacts of the flat cables with cleaning alcohol, one of them had a little bit of rust on it, reassembled everything, and the camera works fine. Except for the excessive power consumption. Sigh.

Annoyed with the battery life of slightly more than one shooting session, I sold the camera and am by now a proud owner of a 450D. Been shooting with a single battery charge for 6 sessions until I had to recharge it. Yay for my first step in the infamous constant gear upgrade path of photographers.

By the way, I had to open the 450D as well, because there was dust inside the sensor, underneath the IR filter glass plate. But that's a different story. Let me just say that Canon did a great job of simplifying the internal design between the 400D and 450D. You don't have to solder at all, and the 450D generally comes apart much easier, even the sensor unit itself [2], [3]. Also, if you try this at home, discharge the flash capacitor. I mean it.

[2] . . .

Tue, 06 May 2014 22:31:26 +0400

Thanks for the thorough update, Markus. It was enjoyable reading the detailed project life of a fellow camera hacker.

Chieh Cheng
Wed, 07 May 2014 04:04:39 +0400

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