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Post by John Farrell on Feb 3, 2016 17:50:46 GMT -5
 Yesterday, I bought a Pentax S1a, which had an interesting fault. When the shutter was cocked, the mirror rose, and the diaphragm stop down plate came forward. When the shutter was released, the mirror and the plate returned to their rest positions. Both shutter blinds travelled together, with no opening. I decided that the problem was with the mirror cocking mechanism - the mirror has its own spring, to drive it. The release cycle is - mirror released; when it reaches the end of its travel, it releases the first shutter curtain; the second shutter curtain follows; when the second shutter curtain reaches the end of its travel, it trips the mirror to allow it to return to the rest position. The front plate of the camera was easily removed - its held on by the 4 screws seen in the picture above. This exposed the mirror mechanism.  The fault was caused by the part you can see above (one end has red sealant on it) being stiff on its pivot, and turned to its release position. This meant it didn't hold the mirror when its spring was tensioned on winding. I put a small drop of oil on the end of the pivot, and now the camera works as it should. |
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Stephen
Lifetime Member
Still collecting.......
Posts: 2,718
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Post by Stephen on Feb 4, 2016 11:50:38 GMT -5
That is a very common fault. Pentax were probably being too accurate in hole size and pivot size, a looser fit would have worked without lube, but they were precision engineers! It may indicate other parts need a touch of oil, the camera may have been stored and used in hot conditions and the oil had dried or creped due to heat. The silicon synthetic oils for model railway use are an easy source of really top grade oil (Labelle etc), or the bit more expensive Nano oil,(a little goes a long way!)
Stephen.
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Post by John Farrell on Feb 4, 2016 13:28:56 GMT -5
I used Singer sewing machine oil, Stephen. And just to show that one shouldn't brag about these things - I wound the shutter and fired it a few times, and now the shutter wind is jammed. While I had the front plate off, one of the springs which holds the prism appeared from under the top plate. I expect to find the other spring blocking the wind gears.
Before I take the top plate off to look, though, I have to finish up the Zenit B I mentioned earlier.......
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Stephen
Lifetime Member
Still collecting.......
Posts: 2,718
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Post by Stephen on Feb 4, 2016 18:46:57 GMT -5
It never rans but it pours.........Genuine Singer oil is good, but can dry up a bit. I am afraid in the UK the stuff sold as Singer is almost certainly not Singer.....more likely from Hong Kong....or China, where Singers are made these days.
Stephen.
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Post by John Farrell on Feb 5, 2016 21:52:42 GMT -5
 It looks like the problem is caused by the silver coloured gear cluster above, binding on its shaft. I've applied CRC, and will check in a few days to see if its free. |
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Post by John Farrell on Jun 6, 2016 22:55:57 GMT -5
For anyone who was following this - the gears are still bound on the shaft. I need to find some sort of (very small) puller, to remove the gear.
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mickeyobe
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Resident President
Posts: 7,280
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Post by mickeyobe on Jun 7, 2016 8:42:34 GMT -5
For anyone who was following this - the gears are still bound on the shaft. I need to find some sort of (very small) puller, to remove the gear. John, I do not have your expertise consequently I always look for the easiest way to do something. May I suggest a judicious application of 1. lighter fluid 2. alcohol 3. WD40. Mickey |
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Post by John Farrell on Mar 17, 2017 17:41:40 GMT -5
Well, I finally got back to this. All that was needed to remove the gear was a firm pull with a pair of pliers. Reassembly beckons.
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Post by John Farrell on Mar 19, 2017 20:58:25 GMT -5
 Well, I've finished putting this back together. It isn't perfect - I didn't take the focusing screen out to clean it, and the mirror has a number of marks on it. It fires on all speeds though. |
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