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Karim
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 17, 2004 - 05:20 pm: | 
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Hi,
I just got a minolta X570 with a problem. I searched the archives but could not find something relevant.
The symptoms :
Everything works OK. Except that the under range LED is always on or blinking.
It's on when the ASA is set at its max value (3200 ASA) AND aperture ring is left alone (with no lens on, ie wide open aperture). If ever I move the ASA dial a bit or move the aperture coupling ring a bit, it blinks. [a bit is around 1-2 stops].
Changing the speed (manual or Auto mode) does not change the state of the under-range LED.
Even with every parameter set 'at best' (3200 ASA/full aperture), the LED is lit.
In Auto mode, when I release the shutter, I get a slow speed (>1s). In manual speed mode, I get what the dial says (1/30 is 1/30). At least, obtained speeds are consistent with what the LEDs say.
The under range LED does not seem responsive at all to light conditions.
What I understand :
As this LED seems responsive to ASA change or aperture change, I think the problem is not coming from the ASA or aperture resistors (I cleaned and checked them for cracks). I checked their wires, too.
The Silicon photo diode has a resistance between 1 and 1.8 Mohm (I unsoldered it and measured the resistance under my working lamp, more or less shadowed). I don't know if it is within specs but it is responsive...
It seems like the light sensitivity of the meter part is shifted out of range.
My guess is that the input voltage from the photo diode to 'the CPU' is too low. Either the photo diode is not enough sensitive to light or the amplifier for this signal is weak.
Other than these theoretical speculations, I don't know where to look at...
The photodiode output goes directly to a chip...
The outside and inside of the camera looks really clean (no crazy tinkering/trim pot messing suspicion..?).
Anybody has a hint ? A 'usual suspect' ?
It's the first Minolta I have in hands (I already like it ), as I'm trying to dilute my Nikon FE Acquisition Syndrom into other brands... ).
I'm used to FE's surgery but not yet to this new baby's...
Sorry for this very detailed post...
Thanks to help,
Karim |
Don
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 19, 2004 - 07:37 am: |
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If the led's turn on w/the main sw, it could be the AE lock sw.( below the ST sw - push down the ST sw) is closed or shorted. Disconnect the yellow wire to the sw. If it now works then there's a prob. w/the sw. If the shutter stays open around 4 sec. on auto then I'd recheck the AV resistor. You should see a smooth change in res. values from min. to max. aperture by checking the brush contact between the blue & orange wires.
Don |
Karim
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 19, 2004 - 10:09 am: |
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Hi Don,
Thanks a lot for this hint... I was stuck...
The Self Timer is working (blinks 10 sec and then shutter activates), but maybe the ST can work and the AE switch can still be stuck...
The shutter can be quicker than 4sec on auto, depending on the Aperture/ASA settings (but always more than 1 sec). I'll check the AV resistor anyway...
I'll try that and post what I find.
In the meantime, I grabbed a XG-9 for 10 euros in a flea market. It seems to have intermittent mechanical problems (mirror stays up or in the middle, shutter fires as soon as wound) but the electronics seem good.
Are some parts of the XG9 swapable with the X570 ?
Thanks and have a nice day,
Karim |
Karim
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 20, 2004 - 07:46 am: |
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Hi Don,
I think the AE swith and AV selector checked OK :
I disconnected the yellow wire from the circuit board, but the Under Range LED is still blinking...
I check the resistance between the orange and blue wires coming from the AV resistor, it moves smoothly when I turn the aperture ring (from 2.43 to 0.6 Kohm). The resistance between the brown and blue wires is steady 2.43 Kohm (which means the brushes are not leaning on the third 'track', I guess).
Those seem OK.
Now, I think I found something interesting on the ASA side :
I removed the ASA and ON/OFF brushes.
I checked the resistance between the brown wire and each of the ASA contacts. It goes from 0 ohm (first contact) up to 6 Kohm (13th contact or so) and then down (!) to 2.43 Kohm (on the last contact).
I expected the resistance to increase regularly from contact to contact, but it increases and then decreases. That looks weird to me. The strip of carbon looks clean and uncracked. No short between the brown and orange wires (2.43 Kohm).
Any ideas ?
Thanks a lot for sharing your knowledge, Don.
Karim |
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