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10-23-2015, 08:33 AM   #1
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K2 shutter speed issues

I have a K2 that I picked up earlier this year, and still never used. It looks in good condition but isn't quite working right. I measured the shutter speeds using Audacity and a little circuit board (all with mirror locked up) and they were all over the place; 1/1000 was anywhere from 1/200 to 1/500, most of the others were a stop too slow, though they varied a lot. Taking the battery out saw 1/125 at 1/90 - this camera should work on B and 1/125 with no power. While checking the speeds, the battery check light was able to function, and I already checked the pair of batteries were producing 2.93V. One oddity is that the check button doesn't always light the LED, sometimes you have to fire the shutter a few times before it will. Sometimes the meter works even when the check LED doesn't.

So, it points towards maybe some connection problems, but maybe also a slow shutter? Any thoughts on where to start looking? The battery holder and compartment look good, and there's nothing obvious under the bottom plate.

Thanks a lot

John

10-23-2015, 12:17 PM   #2
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Sounds like a trip to Eric is in order for your K2. He will fix everything in a CLA.

Here is Eric's website, you can also call or email him:

Pentax Repairs Home

Phil.
10-23-2015, 12:55 PM   #3
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Thanks Phil. Here in the UK we have Robin at Harrow technical but I'm keen to have a stab myself first.
10-24-2015, 01:07 AM   #4
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QuoteOriginally posted by Johnny Rod Quote
I have a K2 that I picked up earlier this year, and still never used. It looks in good condition but isn't quite working right. I measured the shutter speeds using Audacity and a little circuit board (all with mirror locked up) and they were all over the place; 1/1000 was anywhere from 1/200 to 1/500, most of the others were a stop too slow, though they varied a lot. Taking the battery out saw 1/125 at 1/90 - this camera should work on B and 1/125 with no power. While checking the speeds, the battery check light was able to function, and I already checked the pair of batteries were producing 2.93V. One oddity is that the check button doesn't always light the LED, sometimes you have to fire the shutter a few times before it will. Sometimes the meter works even when the check LED doesn't.

So, it points towards maybe some connection problems, but maybe also a slow shutter? Any thoughts on where to start looking? The battery holder and compartment look good, and there's nothing obvious under the bottom plate.

Thanks a lot

John
Have you tried the speeds in manual? It is easy to judge speeds up to about 1/15. If those speeds are good, then maybe the test equipment is out.

10-24-2015, 05:23 AM   #5
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In manual mode the shutter is electronically controlled (as I understand it). The only non-electronic operation is B or 1/125 with the battery taken out - the latter is the fastest flash sync speed FWIW. Auto mode just chooses the speed for you but the actual timing control is still electronic. I've used the same tester on leaf shutter cameras and the numbers look realistic. The only other SLR I tried was my MX which gave 1/800 when set to 1/1000 so again more or less what you'd expect.
10-25-2015, 02:17 AM   #6
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Hi, would you please a explain a little bit more in detail how do you measure the speeds?
The speed controls for the k2 are in the bottom. By just removing the plate, you will see 6 controllers.
10-25-2015, 08:22 AM - 1 Like   #7
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Details here of how to make a circuit to convert light to sound and measure using Audacity:
RaggettĀ·photoĀ·books
I am wondering if the two problems are linked; a intermittent power connection, which is then rattled around when the shutter/mirror fire, and so the speeds are wrong and variable. I guess the first step should be to make sure the power well connected - no dirty switches etc. but I'm not sure which bits to look at.
10-26-2015, 06:37 AM   #8
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I believe it is a simple short circuit that could be caused by a "sulphated" cable, mainly the one that connects the battery to the rest of the circuitry and that the manual speed of 1/125 is simply not calibrated.

10-26-2015, 10:40 AM   #9
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Thanks. I looked under the base plate briefly but saw nothing obviously wrong and put it back. I'll have another look - any other areas I should check? I'm not sure how easy it is to get the top plate off, I have done it on an MX and it was fine. If it can all work as it should then I don't mind about the manual 1/125 being a little off as I doubt I'd use it and the error is overexposure of less than a stop.
10-26-2015, 11:58 AM   #10
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something I just remembered about the k2 is that the asa ring sticks over time, so try to move from one end to the other a few end until you feel it smoother, that could fix the auto speeds. The top plate is not easy to remove, and what I was telling you about the bottom plate is that you will not see nothing wrong, but you will see some kind of volume knobs to tune the speeds, however I sold my Last k2 long ago so I don't have a way to show you which does what...

Last edited by JuanEstrada; 10-26-2015 at 12:11 PM.
10-28-2015, 08:13 AM   #11
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The ISO ring is indeed a bit stiff, but not too bad, it doesn't move end to end but goes from 100 to 800 ISO.

I happened to find a problem with the battery holder. I also have an MX, which (as far as I know) uses the same battery holder. I ended up breaking the female screw thread off the baseplate of the MX, and have only just repaired it. I tried putting the batteries form the K2 (complete with its holder) in the MX and it was dead. Swap the batteries to the MX holder and it works. Putting the "good" battery holder in the K2 also means it works. I had a quick go at shutter speeds and these seem a bit slow but much more reliable. I'll have to test it properly when I have time. It's odd as the battery holder looks fine - there was a little corrosion inside which I scraped off, but even before that it was working. I'll have to soak it in Coke to make sure it's properly clean and try it again but fingers crossed this is the problem. The slow speeds I could live with - 1/1000 was coming out about 1/600 today - if it's reliably slow like some of my others.

Will post again if I find anything else. Juan do you know how to calibrate the mechanical 1/125 speed?
10-29-2015, 03:03 AM   #12
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I spent a bit of time testing the shutter speeds and light meter. Below are the nominal speeds vs. actually measured:

1/1000 was 1/575 to 1/630
1/500 was 1/540-1/510
1/250 was 1/170-1/220
1/125 was 1/75 all three times - I wonder if this is purely mechanical at this speed
1/60 was 1/18-1/40
1/30 was 1/13-1/15

These are all similar but a little slower than my MX, and all much better than my Super A. The meter on the K2 matches the Pocket Light Meter app in ipad, though in brighter light the K2 tends towards 1/3-1/2 stop underexposure (auto is aperture priority mode) so more or less balances out the slow shutter speeds. The 1/1000 is a bit of a disappointment but I'm not sure just how realistic the top speeds of cameras really are, outside of the marketing literature.

So any further thoughts before I give it a try?

Thanks a lot
John
10-29-2015, 08:09 AM   #13
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A service manual for the K2 can be found here:

Pentax Manuals

With a camera of this age the most like reason for the problems you are having is dried up lubricant, I know the shutter speeds are electronically controlled but there are still mechanical parts involved and if the mechanism cannot move freely then the electronic timing will not be correct and it will probably be inconsistent as you have found out..
It is therefore important that everything moves correctly before starting to make adjustments, likewise any corrosion or wiring problems need to be sorted out first.

The preset resistors under the bottom cover are unlikely to need adjusting but if you do intend to alter them make sure you mark their positions first so that you can always reset them to original settings.

The usual tolerance for shutter speeds of this type is +/-25% for speeds below 1/125 and +/-30% for 1/25 and faster.
Also bear in mind that the system you are using with phototransistors and Audacity whilst giving a fair indication it is not the most accurate and could easily account for another 10% of error or more.

Almost all Pentax cameras of this era have a 1/125 shutter speed that actually measured nearer to 1/90 even when new. This came about because of the market pressure at the time to be able to advertise a faster flash synch speed and the only way they could achieve this with the shutter mechanism was to slow things down a bit and then lie about the speed.


Good Luck

Last edited by Ray-uk; 10-29-2015 at 08:36 AM.
10-29-2015, 08:46 AM   #14
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Hi Ray
I believe the 1/125 sync speed of my Super A is also really only 1/90 from the factory too, from what I've read, so I wasn't too surprised to find the K2 isn't too near 1/125 either. In terms of dried lubricant, where would I be looking? I have the service manual you linked to but it's a bit short on detail. I'm (now) much more familiar with leaf shutters pre-1970 than I am with focal plane shutters of any sort, and these run almost entirely without lubricant. Or would I be biting off more than an amateur can chew? This is my latest competed job:
https://flic.kr/s/aHskn9Gmon
so I'm not afraid of having a go.
10-29-2015, 10:38 AM   #15
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All the parts that are likely to be causing your problems are within the shutter mechanism, part E000 on fig 3 of the manual.
You would have to take the shutter assembly out completely which is not a straightforward job and you could very easily end up with even more problems.

Like leaf shutters, only a miniscule amount of oil is applied on the larger moving parts and certainly not the blades, although powdered graphite might help on these ( I've never tried it )

A common problem with this type of shutter is the tiny rubber buffers that act as shock absorbers for the blades when at the end of their travels, the rubber goes soft and the blades get contaminated and cannot move as freely as they should.
If you don't want to attempt a major disassembly then it might be worth trying to wash out any nasties from the mechanism with isopropanol or lighter fluid after removing the top and bottom panels, but don't get it into the prism housing though.

If a wash out doesn't work then you have to decide whether you can live with the shutter as it is or risk stripping it all down with the possibility that it never works again.
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