[reh321]

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Nice hypothesis, but contradicted by the facts. During the time this problem has existed, I have never taken pictures in burst mode, always single shot. Actually, I reviewed each shot before taking the next one, to see if the camera was back to normal.

(In fact, I have never used burst mode in the time I've owned the camera.)

Then this is a completely different problem, because "SHUTTER MECHANISM AND MIRROR MECHANISM" are the words that jump out at me.

[LensBeginner]

I don't see the words APERTURE CONTROL BLOCK... unless by MECHANICAL ASS(EMBL)Y they mean that. I hope you get it back ok, and if not, I hope there's a warranty on the repair.

[Clothears]

I don't see the words APERTURE CONTROL BLOCK... unless by MECHANICAL ASS(EMBL)Y they mean that. I hope you get it back ok, and if not, I hope there's a warranty on the repair.

Thanks. Yes, there's a six-month warranty on the repair. I shall be inclined to ask some questions once I get it back, such as whether I need to treat the camera in a particular way or whether it's a known fault, etc. It's at Pentax's UK repair centre, so I'm hopeful I can find out more later.

By the way, does the word BLOCK in this context refer to a physical item which controls the aperture, or to something which blocks the aperture control from working?

[LensBeginner]

Thanks. Yes, there's a six-month warranty on the repair. I shall be inclined to ask some questions once I get it back, such as whether I need to treat the camera in a particular way or whether it's a known fault, etc. It's at Pentax's UK repair centre, so I'm hopeful I can find out more later.

By the way, does the word BLOCK in this context refer to a physical item which controls the aperture, or to something which blocks the aperture control from working?

"Block" as in "bunch of things screwed together"... they usually change the whole thing instead of just the faulty solenoid.
I'll try and find some pictures tomorrow.

[Clothears]

"Block" as in "bunch of things screwed together"... they usually change the whole thing instead of just the faulty solenoid.
I'll try and find some pictures tomorrow.

Thanks. I had the impression that "Aperture control block" is not an official Pentax phrase/expression but it's useful for me to have that in mind if I get a chance to talk to someone there.

[LensBeginner]

Thanks. I had the impression that "Aperture control block" is not an official Pentax phrase/expression but it's useful for me to have that in mind if I get a chance to talk to someone there.

This is the solenoid, which is the likely culprit of the behaviour:
Pentax K-30 K-50 K-S1/S2 K-500 Genuine Aperture Solenoid Plunger Part - Japan - | eBay
(not my listing)

In this post you can see the whole control block, with gears and a motor.
https://www.pentaxforums.com/forums/151-pentax-k-30-k-50/321871-k-30-k-50-ap...ml#post3656514

[Clothears]

Then this is a completely different problem, because "SHUTTER MECHANISM AND MIRROR MECHANISM" are the words that jump out at me.

Are you sure?

I read the whole of the thread referred to by Lensbeginner now and am inclined to agree with you that the underlying cause is not known (I suppose there could be several). In my case the camera was unused for some three months and thereafter exhibited the problem. That many people reported that replacing the solenoid fixed it does not prove that the solenoid was the root cause.

Perhaps Johnsons Photopia (who do repairs for Pentax in the UK) found extra damage in my K-S1 or perhaps Ricoh really doesn't know what is going on and are just having a bunch of stuff changed to be on the safe side. Nice that they'll do some cleaning though, while it's opened up.

[LensBeginner]

Are you sure?

I read the whole of the thread referred to by Lensbeginner now and am inclined to agree with you that the underlying cause is not known (I suppose there could be several). In my case the camera was unused for some three months and thereafter exhibited the problem. That many people reported that replacing the solenoid fixed it does not prove that the solenoid was the root cause.

Perhaps Johnsons Photopia (who do repairs for Pentax in the UK) found extra damage in my K-S1 or perhaps Ricoh really doesn't know what is going on and are just having a bunch of stuff changed to be on the safe side. Nice that they'll do some cleaning though, while it's opened up.

The cleaning and adjustment is routine after a disassembly.
The solenoid is the cause of the ACB failures a.k.a. dark pictures syndrome, IIRC some people actually shot with the camera open in order to troubleshoot the cause.

The repair estimate looks realistic for a fix of the dark picture issue (on this forum members have spent between 100 and 150 USD), but I don't get the "shutter repair" thing.

[Clothears]

The cleaning and adjustment is routine after a disassembly.
The solenoid is the cause of the ACB failures a.k.a. dark pictures syndrome, IIRC some people actually shot with the camera open in order to troubleshoot the cause.

But what is actually going wrong with the solenoid?

Anyway: my K-S1 just arrived back, took a couple of pics, works OK so far. That's quick work, I only took it to the Post Office a week ago.

Think I'll try and keep it in a plastic bag here (even when inside the camera bag). Environment tends to be dusty, due to being out in the sticks.

[LensBeginner]

But what is actually going wrong with the solenoid?

Anyway: my K-S1 just arrived back, took a couple of pics, works OK so far. That's quick work, I only took it to the Post Office a week ago.

Think I'll try and keep it in a plastic bag here (even when inside the camera bag). Environment tends to be dusty, due to being out in the sticks.

When the electromagnet is activated, it attracts the U-shaped part that slides inside it, and that moving part becomes somehow jammed - because of attrition or magnetism, no one knows for sure.
Since it cannot go back to its original position, the camera closes the aperture fully and doesn't stop at the required f-stop.

[reh321]

Are you sure?

I read the whole of the thread referred to by Lensbeginner now and am inclined to agree with you that the underlying cause is not known (I suppose there could be several). In my case the camera was unused for some three months and thereafter exhibited the problem. That many people reported that replacing the solenoid fixed it does not prove that the solenoid was the root cause.

Perhaps Johnsons Photopia (who do repairs for Pentax in the UK) found extra damage in my K-S1 or perhaps Ricoh really doesn't know what is going on and are just having a bunch of stuff changed to be on the safe side. Nice that they'll do some cleaning though, while it's opened up.

I am sure now, that the aperture control unit {a.k.a. "block"} design dates back thirty years.
K-500 Aperture block failure? - Page 2 - PentaxForums.com

I am fairly sure that this whole problem surprised Pentax.

Other than that, I'm not sure of much of anything - I try to label my opinions as opinions, but sometimes I forget.

[Wingincamera]

I don't know what Precision charges for the aperture block repair, I sent my K-S2 to Pentax Camera Repair - Aperture Control Repair for repair. It cost $100.00 (US) plus shipping. Took about a week to return to me. The camera works great.

[LensBeginner]

I don't know what Precision charges for the aperture block repair, I sent my K-S2 to Pentax Camera Repair - Aperture Control Repair for repair. It cost $100.00 (US) plus shipping. Took about a week to return to me. The camera works great.

Price is right - on the lower end of the spectrum (100-150$) actually.
Nice to hear your camera is now fine as well

[Clothears]

Was at Queen's Club for quarter-finals day last Friday. Wifey took lots of pix with the K-S1 using our the 55-300, but mostly at 300. None of them particularly sharp or well focussed, and our seats were not well placed vis-a-vis the sun, even using the lens hood. Some bright white seats in the club-house opposite which tended to bleed. After running these into LR it seems that the camera, although working consistently, still underexposes by about a stop. Hmmm, time to panic.

So today I took a couple of shots of the chimney stack on the roof here against the sky using various primes (35 f2.4, 50 f1.4, 100 f2.8) all at ISO 100, f 5.6, Av mode, bright sunlight. Some relief to see them all process to sharp images, even better when I went out again and repeated at f8, ISO 400 (although some noise was apparent in the sky when pixel peeping).

Looks like I need to get shutter speed down to 1/1000 or faster with the 55-300, so I may try using ISO 800 when we go to Wimbledon next week, or take the 100 and crop the images.

[LensBeginner]

Was at Queen's Club for quarter-finals day last Friday. Wifey took lots of pix with the K-S1 using our the 55-300, but mostly at 300. None of them particularly sharp or well focussed, and our seats were not well placed vis-a-vis the sun, even using the lens hood. Some bright white seats in the club-house opposite which tended to bleed. After running these into LR it seems that the camera, although working consistently, still underexposes by about a stop. Hmmm, time to panic.

So today I took a couple of shots of the chimney stack on the roof here against the sky using various primes (35 f2.4, 50 f1.4, 100 f2.8) all at ISO 100, f 5.6, Av mode, bright sunlight. Some relief to see them all process to sharp images, even better when I went out again and repeated at f8, ISO 400 (although some noise was apparent in the sky when pixel peeping).

Looks like I need to get shutter speed down to 1/1000 or faster with the 55-300, so I may try using ISO 800 when we go to Wimbledon next week, or take the 100 and crop the images.

About a stop is nothing to be concerned about, probably just the meter being fouled by shooting against the sun.
Also check metering mode (spot, center weighted, smart etc.) and exposure compensation.

The difference with the ACB control block failure should be the one between the shooting aperture and the fully closed one (f/22, f/32).