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09-07-2009, 01:51 PM   #1
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An odd K-7 / DA*50-135 crash...

New K-7 arrived, battery fully charged, time to get familiar...
I mounted several lenses on the K-7, took some test shots
all looks great. as advertised...
Well, almost all.
My beloved Pentax DA*50-135 is the exception.

When I have it on the K-7 and try to auto focus, the lens does not move, and after a few seconds, the camera shuts down, and won't start again. I switch it off, and on again - no LCD, no Monitor. dead.

Took out the battery - put it back in the charger for no more than 10 seconds, then back in the camera - all is well again, battery indicator says "full".

All other lenses work beautifully (DA*16-50, DA 21 ltd, FA 77 ltd, sigma 70-200/2.8, Tamron 28-75, Pentax FA 35, and more...)
All except the 50-135.
But the very same 50-135 works great on my K20D body !!!
What is it that makes the K-7/50-135 combo to crash?

A few more technical observations:

a) I know that my 50-135 has a bit of a mechanical problem, which you can feel by manual rotation of the focusing ring. not moving smoothly... yet, the K20D handles it well (optically - the lens is superb).

b) How come the battery appears "dead" - when it is not. when I take it out after the crash, my digital multimeter shows nearly 0 volts between all terminals. Yet, just a few seconds in the charger brings it back to life, with "full" indication on the LCD

A 1860 mAH battery stores a lot of energy. If it had really discharged in say 10 seconds of use with the 50-135 lens, it would have to be a "short circuit", with a lot of current and heat. none of this happens.
Could the D-LI90 battery have some kind of a protection shut down in it?

I am temporarily suspending the use of the 50-135 on the K-7

Does anyone have any idea, or a similar experience?
many thanks
Itzik

09-07-2009, 04:57 PM   #2
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That is odd... i'd start with checking the electrical contacts on both body and the lens... and upgrading the firmware on the body....
09-07-2009, 05:35 PM   #3
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Doesn't sound like the K-7's electrical contacts either - the 16-50 works fine...
Hmm, strange...
If your 50-135's under warranty, best to have it checked out before things get worse with the focusing.
Otherwise I'm at odds as to what's going on...
09-07-2009, 10:41 PM   #4
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dude if you had just opened the camera, and popped the battery in, and it says full, its not. Charge the battery fully, then try again. i bet the SDM pulls more electricity than a dead battery can deliver. you need more than 10 seconds to charge a battery. oh yeah, clean the contacts on the 50-135. they can get dirty and confuse the camera, i have had it happen.

09-07-2009, 11:27 PM   #5
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Is there some sort of electronic circuit breaker in the battery pack, it sounds as if the lens is binding and the excess current is opening some kind of current limiter or circuit breaker?
09-08-2009, 12:34 AM   #6
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First - charge your battery fully, then make tests
09-08-2009, 05:16 AM   #7
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QuoteOriginally posted by Vaikis_ Quote
First - charge your battery fully, then make tests
Thanks... it never occured to me to charge my battery before shooting..
now seriously guys. Give me some credit, OK?
I think what I am describing here is odd & interesting, and deserves some thinking...
Let me re-cap the main points:
K-7 with a fully charged (repeat - fully charged) battery, takes on the DA*50-135.

A lense that works regularly on both my K20D, and the old *istD.
Works - but has a mechanical problem in the focusing drive mechanism (friction, feels like sand paper when manually focused)
It is definitely a problem that should be fixed - but both K20D and *istD manage to focus well, friction and all....

With the K-7: when I press the shutter button to focus, the lense does not respond. If I persist for just a few seconds - the camera shuts down, and will not turn on.
I take the battery out, check the voltage at the terminals with a multi-meter - almost zero.
Basic physics: this is a 1.86 Ah battery (remember - fully charged...). There is no way for this battery to fully discharge in say, 10 seconds, without excessive heat, current, sparks... there is the large stored energy that should dissipate somehwere...
I think we can safely assume that during this short focusing attempt with the 50-135, the battery did not really discharge. Perhaps (and this is a speculation), my lense does draw excessive current for focusing, and that there is some kind of a protective shut-down mechanism in the D-LI90 battery, which triggers by the extra current.
I wonder if this is a valid assumption...this is my only plausible explanation for the battery "appearing" dead... Is it also possible that this protective shut-down did not take place on the K20D and *istD simply because their batteries do not have this protective feature of the D-LI90?

I then put the battery back on the charger for just a few seconds.
Yes, I know that one does not charge a battery in 10 seconds...
But it so happens, that the charger "awakens" the battery from its shut-down state, back to life
and once again - I am sure that the battery did not lose any significant charge during this episode, therefore still fully charged.

So, what is the bottom line?
1. I certainly need to have my 50-135 repaired... (out of warranty...)
2. It is still intereting to understand the behaviour of the battery. Is it really an innovative protection device that triggered, or else what?
wonder if any one can have more on this..?..
09-08-2009, 05:21 AM   #8
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if possible, check your DA* 50-135 with another K-7 body

09-08-2009, 06:11 AM   #9
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QuoteOriginally posted by Itzik Quote
2. It is still intereting to understand the behaviour of the battery. Is it really an innovative protection device that triggered, or else what?
wonder if any one can have more on this..?..
Interesting observation, but did you charge your battery Sorry couldn't resist.

So have we finally found the reason for the new battery, to protect SDM lenses that have failed?

Thank you
Russell
09-08-2009, 06:55 AM   #10
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could be something as simple as this:

MOSFET-based battery protection systems - Electronic Products

But I can't find any information on the D-Li90 battery to confirm, and short of ripping apart my brand new battery to find out, I guess we will have to wait for somebody else to come up with the answer! ;-)
09-08-2009, 07:08 AM   #11
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QuoteOriginally posted by Tristar Quote
Yes. I think your link is very relevant, and makes a lot of sense.
An internal current sensing device, which opens a series MOSFET switch.
Thinking of it, I will not at all be surprised if it has some sort of a built in timer, to re-activate the battery after a while.
The reason I put the battery on the charger to re-activate was purely intuitive.
Perhaps in a minute or two it would have happened automatically.
Maybe I should risk another test...
Interesting link. Thanks
09-08-2009, 08:36 AM   #12
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Maybe not relevant, but the third time I used my 50-135 on my K-7, the SDM failed and never recovered. I never tried it on another body, but did try cleaning the contacts, etc., and I could hear the SDM trying to work. Plus, my 16-50 is fine, so I didn't blame the camera.

Could it be a voltage issue?

Can't experiment further though--I sold my 50-135 as-is... So maybe I don't want to know how this ends!
09-08-2009, 11:58 PM   #13
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Did you charge the battery?


Bad taste but... a little humor for a bad situation.


I believe from a logical view point you have to be right. The battery is not losing all its charge, the battery must be shutting down. The lens must be doing something to draw a lot of current from the camera. Now this is just great. If Pentax made the battery a bit safer with over voltage/current protection and now DA*50-135mm owners who use to be able to bring the lens back to life by constant playing on/off games for a period of time. Now you can't even do that because the new battery shuts down.

BTW most all batteries for digital cameras have over-heat protection I believe, if I remember correctly, this is why they say not to use third party batteries, it may not have any of the safety features. However the new battery seems to be fully protected or protected in a different better way.
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