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Steve Roberts
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 21, 2006 - 02:17 am: | 
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Hi All,
I'm trying to resurrect a Pentax ES, which I know isn't the most beloved of SLRs to the repairer. The problem is that the shutter fires OK on manual settings, but on automatic although the correct speed is indicated by the meter, the shutter seems to fire only at a fixed very fast speed.
I have a copy of the Pentax repair manual and a copy of the excellent 26 page article from "Camera Craftsman". From these I gather that the second shutter curtain should only be released when the supply to the electromagnet is discontinued, as controlled by the timer circuit. Hence, my reasoning is that with the camera dis-assembled and the battery applied straight across the electromagnet contacts (circuit board removed) the shutter should open but not close until I disconnect the supply to the magnet. Am I correct in this? What actually happens is that the shutter just opens and closes, kicking the electromagnet catch out of the way as if it was not energised.
The electromagnet shows the correct 320 ohms resistance and is working, but I wonder if its position needs adjusting so that it holds back the second curtain for the desired time?
I'm hoping to establish whether or not the electromagnet is operating correctly before investigating the timed supply to it. One other query - the timing capacitor doesn't appear in the same position as shown in the Camera Craftsman article, ie lying in a cut-out at the edge of the circuit board. I suppose I may have an earlier or later model - does anyone know where the capacitor has moved to?
Any help or suggestions much appreciated for this beast which (apart from the fact that it doesn't work!) is far too good for the dustbin!
Many thanks,
Steve |
Steve Roberts
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, February 24, 2006 - 05:06 am: |
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Update.
Well, after a "nil response" to my question, I have now answered it myself. On removing the electromagnet, I found that someone had adjusted the hinged plate that carries the armature and spindle so that the armature was no longer flush with the top of the two poles of the magnet and hence its holding ability was vastly diminished. I re-set this and, as suspected, firing the shutter with the magnet energised left the shutter open and only closing when the supply to the magnet was removed.
On reassembling the camera, it is apparent that the electronic shutter works after a fashion, but not as it should. The correct shutter speed is indicated, but the electronic control of the shutter is only apparent at indicated speeds of a second and longer. It's as if the action of the electronics is no longer linear but logarithmic, with all the action at the slow end of the indicated speeds and anything shorter than a second getting a standard 1/1000th.
I feel that I'm 90% there, but that something is still wrong beyond an adjustment. I fitted the main PCB to my ESII and all seemed to be well, so I'm discounting that. The cells are giving the correct indication, so are probably OK and so I'm left with the only other piece of electronics - the memory block, which is just a switch, capacitor and FET.
Any advice or thoughts welcomed!
Steve |
Berk Sirman
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 27, 2006 - 03:02 am: |
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Have you checked the archives or yahoo's spotmatic group? I recall a similar issue was discussed some time ago. If it is not in the archives I am sure there'll be someone there who will know about this. Most probably Gene Poon.
http://groups.yahoo.com/group/Spotmatic/ |
Steve Roberts
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 27, 2006 - 04:51 am: |
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Thanks, Berk, but I've found the source of the problem. When the shutter is cocked the mechanism attached to the red/black indicator should close a switch, shorting the timing capacitor and preventing it from accepting a charge until the switch is opened by releasing the shutter. This wasn't happening. The adjustment is by a setscrew (which forms one of the contacts) and a locking nut, mounted on a small fibre glass strip. Someone had fiddled with the two screws securing the strip to the body so that the setscrew adjustment did not allow it to meet the moving contact. I tweaked the assembly so that the contacts just meet when the shutter is cocked and the camera now behaves as one would expect. I don't know the proper procedure for setting the adjustment (it's not mentioned in the Pentax repair manual beyond "leave well alone") so I'll leave it like that and hope that I can "fine tune" things via the preset pots on the circuit board.
People generally seem to regard the ES and ES2 as the lepers of the camera world, but having delved into one, it's a very clever system that has taken the basics of a Spotmatic and adapted it for electronic control of a tried and tested mechanical shutter.
Steve |
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