HW failures on Canon Compacts - General Discussion and Assistance - CHDK Forum
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HW failures on Canon Compacts

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Offline koshy

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HW failures on Canon Compacts
« on: 20 / July / 2014, 16:08:27 »
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I saw an odd behavior on A630, A640, A550. I'm not even sure if it's CHDK related but I think it more likely is than isn't. I didn't test the cameras without CHDK.

Anyway, what happens is that on occasion after turnig the camera on in shooting mode it doesn't display a scene but displays a black screen. When one takes a picture when that happens one gets a dark frame photo. One can use PS > Image > Adjustments > Equalize on the extracted sensor data from a DNG to show that the resulting data is sensor output (it contains the expected sensor noise and not just one uniform color value). When this occurs it can be defeated by toggling back and forth between play mode and shooting mode and/or by turning the camera on/off.

Does this give anyone an idea? Have you seen similar effects?
« Last Edit: 22 / July / 2014, 07:10:37 by koshy »
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Offline srsa_4c

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Re: Bug Report? A630, A640, A550
« Reply #1 on: 20 / July / 2014, 16:44:03 »
HW fault: the mechanical shutter starts to stick OR the shutter cable inside the lens starts to break.
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Offline koshy

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Re: Bug Report? A630, A640, A550
« Reply #2 on: 20 / July / 2014, 16:48:17 »
Ah, that could be an explanation.
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Offline koshy

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Re: (likely to be a HW failure) Bug Report? A630, A640, A550
« Reply #3 on: 22 / July / 2014, 07:05:30 »
We have named one HW fault above but I saw two others - can someone put more information on what actually failed in the following two cases?

a) Camera generates images that are covered with horizontal stripes all over (has to be some sensor defect)
b) Camera overexposes all images (except in very dark room) (has to be a shutter problem)

Can any of that be fixed with reasonable effort?
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Offline waterwingz

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Re: (likely to be a HW failure) Bug Report? A630, A640, A550
« Reply #4 on: 22 / July / 2014, 08:35:44 »
My guesses ?

Quote from: koshy on 22 / July / 2014, 07:05:30
a) Camera generates images that are covered with horizontal stripes all over (has to be some sensor defect)
How tall are the stripes?  Could be something in the sensor read-out amps or possibly an error in the RAM used to recieve sensor data.  Not fixable in software - likely requires complete replacement of the sensor and/or camera electronics.  Nasty.

Quote
b) Camera overexposes all images (except in very dark room) (has to be a shutter problem)
AFAIK,  the shutter just cuts of light from saturating the sensor when nothing is going on. The actual exposure time is determined in the electronics by the sensor integration time.  Overexposure implies that something is off in the calibration of the sensor - might be caused by age?  In  any case, does the camera's Ev offset +/-  correct it linearly over different scene illuminations?  You could use CHDK to override exposure in a non-linear fashion if not - assuming the overexposure is constant for a given scene illumination level?

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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline koshy

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Re: HW failures on Canon Compacts
« Reply #5 on: 22 / July / 2014, 09:26:42 »
Quote from: waterwingz on 22 / July / 2014, 08:35:44
How tall are the stripes?
I'll attach a 100% crop. They are 1px tall. Well visible from DNG, garbled due to sharpening etc. in JPEG.

Quote from: waterwingz on 22 / July / 2014, 08:35:44
Overexposure implies that something is off in the calibration of the sensor - might be caused by age?  In  any case, does the camera's Ev offset +/-  correct it linearly over different scene illuminations?

Both cams are kind of ancient. Ixus 50 and A430. I thought it was two problems yesterday night but they each have both the stripes and the over exposure it seems.
I set the TV Override to short Exp via CHDK using 0.01 and 0.001 and that gives the same result in terms of brightness. +/- has no effect either. The pecular thing is that the live view preview image adjusts fine to lighting changes.
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Offline koshy

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Re: HW failures on Canon Compacts
« Reply #6 on: 22 / July / 2014, 09:36:04 »
A quick look at uninterpolated data is interesting, too. On the white flower pot to the left of my original crop we can observe that there is a difference that spans over 4 sensor lines and then starts over. It seems to start very bright and get gradually darker three times and then starts over. The attached was scaled to 400% - obviously using nearest neighbor.
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Offline waterwingz

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Re: HW failures on Canon Compacts
« Reply #7 on: 22 / July / 2014, 09:42:43 »
Quote from: koshy on 22 / July / 2014, 09:26:42
I set the TV Override to short Exp via CHDK using 0.01 and 0.001 and that gives the same result in terms of brightness. +/- has no effect either.
Do Tv overrides of 1.0 or 0.1 do anything?
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Ported :   A1200    SD940   G10    Powershot N    G16
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Offline Microfunguy

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Re: HW failures on Canon Compacts
« Reply #8 on: 22 / July / 2014, 09:52:55 »
Looks like the mechanical shutter is slow or not working.
The sensor is being exposed to light while the charge is read out.

I have had that problem with cameras that I hacked (removed lens) years ago and attempted to fit a DIY shutter.

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Offline koshy

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Re: HW failures on Canon Compacts
« Reply #9 on: 22 / July / 2014, 09:55:10 »
Quote from: waterwingz on 22 / July / 2014, 09:42:43
Do Tv overrides of 1.0 or 0.1 do anything?
Yes, 0.9 gives total over exposure => white JPEG.

DNG shows a little substance in the very dark regions and gives a pretty dead pixel map.
« Last Edit: 22 / July / 2014, 09:59:27 by koshy »
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Koshy had a little ELPH which wasn't white as snow but everywhere that Koshy went the ELPH was sure to go. (actually an SD, but that detail ruins the rhyme...)
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