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01-05-2019, 03:30 PM   #1
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For the engineers out there-- aperture block , or battery failure?

My K50 recently decided to give the dark picture syndrome. Having little to do today, it was playtime. Charged a Pentax battery (1050ma), a Wasabi (1400ma), and the aa adapter with 2450ma batteries. With the Pentax battery the actuator block would not work. With the Wasabi, it would work occasionally, with the aa's it worked every time. It would appear to me this is a current problem rather than a failure of the block. As the Pentax battery is nearly three years old ( as is the Wasabi), it seems they no longer have the power needed to work the block. I'd like to see someone with more experience look at this and see if that is looking in the right direction.

01-05-2019, 05:53 PM - 2 Likes   #2
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It's both aperture block and battery/current. The way it works is that a current creates a magnetic field that allows the solenoid to switch states. When the aperture block is failing, the small horseshoe shaped plunger has become magnetised enough so that the solenoid has no affect on it, so it just sits there and the aperture doesn't open.

By filing the plunger you get slightly less magnetic force so it can be moved when the solenoid is activated.

...or if a stronger battery is provided the current produces a field strong enough for the block to work 'normally'.
01-05-2019, 06:25 PM   #3
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QuoteOriginally posted by photosrus Quote
My K50 recently decided to give the dark picture syndrome. Having little to do today, it was playtime. Charged a Pentax battery (1050ma), a Wasabi (1400ma), and the aa adapter with 2450ma batteries. With the Pentax battery the actuator block would not work. With the Wasabi, it would work occasionally, with the aa's it worked every time. It would appear to me this is a current problem rather than a failure of the block. As the Pentax battery is nearly three years old ( as is the Wasabi), it seems they no longer have the power needed to work the block. I'd like to see someone with more experience look at this and see if that is looking in the right direction.
Welcome to the Pentax Forums!

You may be correct and other users have reported similar behavior. That being said, the capacity figure (mAh) printed on the battery is not an indicator of instantaneous current (coulombs/sec) without voltage drop (i.e. "power"); rather, it is the charge capacity of the battery and may be directly converted to coulombs. The two are related, but not the same. Based on other user's experience, you may expect the problem to worsen until the aperture block fails regardless of power source used.


Steve

Last edited by stevebrot; 01-05-2019 at 06:31 PM.
01-05-2019, 07:10 PM   #4
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QuoteOriginally posted by HarisF1 Quote
It's both aperture block and battery/current. The way it works is that a current creates a magnetic field that allows the solenoid to switch states. When the aperture block is failing, the small horseshoe shaped plunger has become magnetised enough so that the solenoid has no affect on it, so it just sits there and the aperture doesn't open.

By filing the plunger you get slightly less magnetic force so it can be moved when the solenoid is activated.

...or if a stronger battery is provided the current produces a field strong enough for the block to work 'normally'.
The problem here is that a few people that have filed down the plunger report that there is no evidence that the plunger has been magnetized. The metal filings are not attracted to the plunger or the file.

There has been much discussion on the topic of the failure and along the lines of parts getting magnetized or current/power problems. The discussion tends to get dominated by one or two individuals and further discussion gets stifled.

01-05-2019, 07:29 PM   #5
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QuoteOriginally posted by Not a Number Quote
The problem here is that a few people that have filed down the plunger report that there is no evidence that the plunger has been magnetized. The metal filings are not attracted to the plunger or the file.
The most recent wisdom as I understand it is that there is greater physical resistance over time due to the type of plastic used in the guide sleeve. Filing has fallen out of vogue in favor is simply replacing the part using a suitable donor body or similar.


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01-05-2019, 09:39 PM   #6
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It is true that many people find they can get a bit more life out of the aperture block with aa ni-mh batteries primarily. But eventually even this fails, and then when they replace the block, the older batteries work normally again.
01-06-2019, 11:56 AM - 1 Like   #7
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QuoteOriginally posted by UncleVanya Quote
It is true that many people find they can get a bit more life out of the aperture block with aa ni-mh batteries primarily. But eventually even this fails, and then when they replace the block, the older batteries work normally again.
With my K-30, I reached the point where it would work with partially-charged AA-batteries but not with the same batteries fully charged .... then came Black Friday and a $700 KP.
01-07-2019, 10:57 AM   #8
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QuoteOriginally posted by HarisF1 Quote
It's both aperture block and battery/current. The way it works is that a current creates a magnetic field that allows the solenoid to switch states. When the aperture block is failing, the small horseshoe shaped plunger has become magnetised enough so that the solenoid has no affect on it, so it just sits there and the aperture doesn't open.

By filing the plunger you get slightly less magnetic force so it can be moved when the solenoid is activated.

...or if a stronger battery is provided the current produces a field strong enough for the block to work 'normally'.
I used the filing method. Worked perfectly.

01-07-2019, 11:11 AM   #9
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QuoteOriginally posted by labidas Quote
I used the filing method. Worked perfectly.
Same, fixed yet another just the other day. I've given one to my younger brother and will be keeping one for the giggles. Might even stick it in my car with an old lens.
02-01-2019, 05:19 PM   #10
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QuoteOriginally posted by labidas Quote
I used the filing method. Worked perfectly.
I just replaced the solenoid in my K50 with one from a laptop DVD drive last night and it works fine. The old DVD drives are very common and cheap so I think are a good source of solenoids. You need to take the camera apart either way so I preferred to replace the part rather than try to get the existing one working again.
05-20-2019, 02:47 PM   #11
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I have a K-S2 with the "dreaded ABF," and I've read about the "fixes" that involve burst shooting, setting the RAW/Fx button, etc.

But is there a concensus that, in the long run, the issue will worsen and can be resolved only with the small malfunctioning horseshoe solenoid piece replaced with a working one?

Thanks!
05-21-2019, 08:30 AM   #12
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My K-50 recently started to produce the occasional dark (fully stopped down) image. It gradually got worse so I swapped the K-50 solenoid for one from the flash pop-up in an *ist DL2.


Sadly it didn't fix the problem for long. Also, the suspect solenoid from the K-50 works fine in the *ist DL2.


I think the fundamental problem (at least with my K-50) is with one of the two torsion springs in the aperture control block. I've not taken the block apart yet (I'm waiting to obtain an offset screwdriver) but I suspect the spring has unclipped or has become too weak to pull the plunger out of the solenoid. If it's the later I will try making a slightly stronger spring.


A weak spring would probably explain why the mechanism is so sensitive to slight variations in voltage and differences in solenoid extraction force.
05-21-2019, 05:11 PM   #13
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QuoteOriginally posted by mlynch53 Quote
I have a K-S2 with the "dreaded ABF," and I've read about the "fixes" that involve burst shooting, setting the RAW/Fx button, etc.

But is there a concensus that, in the long run, the issue will worsen and can be resolved only with the small malfunctioning horseshoe solenoid piece replaced with a working one?

Thanks!
Yes, it is the consensus that the only real fix is replacing the solenoid. The only points of contention is the type of solenoid which can be used as replacement.
05-27-2019, 06:22 AM   #14
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There's no consensus. Replacing and filing both work for an unknown amount of time. There's no guarantee the problem won't come back. After all, we are not Pentax technicians here.
05-27-2019, 05:43 PM   #15
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I wasn't aware of any reports of people replacing the solenoid and everything working, with a repeat of the failure some time later? Do you have any links?
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