My 550 developed the same problem in 2005. I found mentions online about wiring coming loose from the circuit board due to heat exposure. Some felt it was a defect Pentax should have fixed free, others admitted they may have left the camera in hot cars, etc. I got a new camera but always wanted to get the 550 fixed as it is a really sweet camera when it was working. Brokencamera.com says they can fix for between $70-$100. I think I'm going for it.
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