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Re: [OM] Update on Om-2n problems

Subject: Re: [OM] Update on Om-2n problems
From: HI100@xxxxxxx
Date: Mon, 29 May 2000 01:54:32 EDT
Cc: lo@xxxxxxxx
Lyle  (lo@xxxxxxxx)  asked:

<<
 I don't have the mirror lockup on auto--it fires ok--but I seem to have the 
same shutter speed (1/60 I would estimate from the sound of it) on auto no 
matter what the aperture setting.  Would this similarly indicate either photo 
diodes or switch as in the case of the  mirror lock-up? On manual works ok, 
but these are different detectors aren't they?.  Are photodiodes still 
available, and is this a job a handy person could do, or is it off to the 
shop 
>>

1) Yes the detectors are quite different on manual. 
    But if the shutter speeds vary correctly when the shutter speed dial is 
changed in manual this does indicate almost all the electronics for Auto are 
working.
2) If one or both of the photo diodes were leaky or shorted it might well 
cause the shutter speeds to always be some fast value. Or if the circuit 
board were badly contaminated it might also cause similar symptoms. If all 
times are correct on manual then the rest of the parts ,amplifiers cct bds 
etc are all working correctly.
3) If the switch were defective or both diodes open circuit it would tend to 
cause lockup since the normal LED exposure limiter would not work if the 
photo sensors do not work.
4) If the photo diodes are available it is still relatively difficult to work 
on the boards as they require extreme cleanliness and they require use of 
silver alloy solder (metalized ceramic) and extreme static precautions as the 
diodes connect to unprotected Mosfet transistors. If the photodiodes are not 
available it should be possible to get suitable substitutes although diodes 
with the right filtering ("blue enhanced" etc) are harder to get and some 
sort of crude lens may be necessary. It is probably necessary to recalibrate 
auto mode with any new sensor. 

Regards,
             Tim Hughes
         >>Hi100@xxxxxxx<<




 

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