Pentax S1a - Shutter Problem

Steve Smith · Jan 24, 2009

I have been given a Pentax S1a. Initially it had a problem with the shutter speeds slower than 1/30 where the second curtain would not close. A quick look under the bottom plate found the problem and after a slight re-bending of a piece which holds the second curtain open, the shutter now opens and closes on all speeds.

The problem is that the speeds below 1/30 are all very fast and seem to be the same.

I have not checked 1/30 and faster yet but they seem to get progressively faster when viewing a light source through the open back.

My question is this: Do the speeds below 1/30 use a different mechanism which somehow is not engaging now?

If that is the case and speeds from 1/30 to 1/500 (and perhaps the 'hidden' 1/1000) are o.k. then I will not try to repair the slower speeds and just use it from 1/30 upwards. I almost always use 1/125 hand held anyway.

In all other respects, this camera is in excellent condition and it would be a shame not to use it.

Steve.

John Koehrer · Jan 25, 2009

Steve,
Yes, the slower speeds use an escapement mechanism to control the timing.
If the 2nd curtain wasn't closing, the curtain travel times most likely needed to be adjusted. This is done with the worm gears visible beneath the bottom plate and probably very near the lever you bent.

Steve Smith · Jan 25, 2009

Thanks for the info.

Initially on speeds slower than 1/30, the first curtain would open but the second curtain wouldn't close. I noticed that a small pressure on the little lever I mentioned released the second curtain so I bent it down very slightly.

I will have another look at it but if it is working from 1/30 and faster I might just leave it alone. I can use the oscilloscope and a photo-diode at work tomorrow to check the shutter speeds.

Steve.

Steve Roberts · Jan 26, 2009

Hi Steve,
I acquired a Spotmatic with no speeds slower than 1/30th for no other reason than it was very cheap!. As John says, it's almost certainly the slow speed escapement. I dismantled the Spotmatic, which necessitated removing the mirror box, freed the escapement mechanism with a few drops of lighter fluid to dissolve the ancient, gungey lubricant and then once the mechanism was moving freely re-lubricated it. Not a difficult job, just one requiring a bit of patience and a set of jeweller's scredrivers. A good job for a cold winter's evening! If you do decide to give it a go I can send you some disassembly info if needed.

Steve

Steve Smith · Jan 26, 2009

Thanks.

I have tested the speeds fom 1/30 upwards and they seem to be o.k. so I will probably leave it alone.

My curious side is interested though. If you have any info or pictures from your repair and it's not too much trouble, I would be interested in seeing it.

Steve.

Ian Grant · Jan 26, 2009

Back in the UK I have an older Pentax that needs repair, I was given it broken. The shutter blinds need re-attatching, any info on how you disassembled your S1a would be useful, mine's an S.

Ian

Steve Smith · Jan 26, 2009

I have only taken the bottom plate off of mine so far (just four screew on the base). I don't really want to go any further as it is in a useable condition right now. Sometimes my repairs turn cameras into a pile of spare parts!

Steve Roberts' Spotmatic repair may provide you with more useful information though.

Steve.

Ian Grant · Jan 26, 2009

Too many Steve's I meant to ask Steve Roberts

Ian

Steve Smith · Jan 26, 2009

Thought so. Except you said S1a!!

This could be useful: http://www.lensinc.net/pentaxrepair.html But as a last resort as it involves spending money. $5.95 !!!

Steve.

Steve Roberts · Jan 26, 2009

Steve and Ian,
There are two Spotmatic repair manuals downloadable for nowt at Dead Link Removed
One is the manufacturer's and the other produced by National Camera. The Spotmatics and S1a/S's have some parts/assemblies that are remarkably similar and some that are quite different (such as the exposure counters) but a look at the Spotmatic info should give you the general idea. Watch out for anti-clockwise threads around the exposure counter - these seem to vary so if something won't come undone easily have a close look at any exposed part of the thread. Ian - re-attaching the shutter blinds is something I've only read about (in Tomosy vol 1). Personally, I'd think long and hard before tackling that!

Steve

Ian Grant · Jan 26, 2009

Thanks Steve. My camera's always been a paper weight so nothing ventured nothing gained

Ian

John Koehrer · Jan 26, 2009

The really neat thing about the Spotmatics is the front plate is so simple to remove.
Remove top, bottom covers & leatherette. The screws for the front plate are now visible. DANGER! Will Robinson! There are usually small shims beneath the plate. They are used to set the film/flange distance.
Sometimes they will stick to the back of the plate, sometimes to the casting and sometimes just not there.
There is also a small shaft ~2mm long that engages the self-timer lever to the ST itself. Just make sure you don't lose it, it needs to be engaged for the timer to work.

Steve Smith · Jan 26, 2009

Someone on the Flickr Manual Pentax group pointed me here: http://www.pentax-manuals.com/manuals/service/servicemanuals.htm

The first manual for the S3 is just about the same as the S1a. Some files need the password 'Pentax' to open (P must be capital letter).

Lots of other interesting stuff there too.

Steve.

Ian Grant · Jan 26, 2009

Thanks Steve, that's my beast - I think, an S3. I've always left it lying about with a few lenses in case I was burgled It looks OK

Ian

Steve Smith · Jan 26, 2009

Fixed it!!!

Thanks to the S3 service manual, I found a lever which was out of place. After lots of attempts taking it apart and putting it back together again involving the usual quota of swearing, it now works on all slow speeds.

1 and 1/2 seconds are a bit hesitant but not far off, 1/4, 1/8 and 1/15 seem o.k.

B works but T just fires quickly. I assume T is press once for open, press again for close. I don't really care that T doesn't work.

During repeated testing there were a couple of misfires where a low speed fired faster (probably 1/30) but 95% of the time it was fine.

I'm probably only going to be using this hand held between 1/60 and 1/250 (judging by my usual exposure information) so I didn't really have to do this slow speed repair but I'm glad I did just for the practice.

EDIT: And just to round off the evening, I managed to fix our washing machine too!

Steve.

Pentax S1a - Shutter Problem

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