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04-17-2012, 03:07 AM   #1
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Pentax 67 TTL pentaprism meter problem?

Hi!

I'm not even sure this is a real problem...
I have a Pentax 67 with TTL pentaprism and the meter is constantly metering.
I mean, is it not supposed to turn off when I switch the on/off button? And should I not have to turn it on with the on/off button in the first place? Won't this shorten my battery life quite fast?

(I mounted the pentaprism first and then the lens according to the manual ...)

It would be great if someone had an idea what's wrong if anything ..

Cheers!

04-17-2012, 11:11 AM   #2
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Hi,

Does it come on as soon as the TTL Prism is mounted? If yes, then the switch inside is shorted out by something or a component has gone bad letting current into the switch/gate.
If no, then the physical switch possibly fine.
When you turn it on and the meter comes to life and refuses to turn off then the time swicth in the circuitboard is bad.

Thats my guess?

...I've worked on a dead TTL before.

Last edited by MysteryOnion; 04-17-2012 at 02:16 PM.
04-17-2012, 02:25 PM   #3
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Hi,

it only switches on with a lens mounted.
After lots of trying I found out that I can turn it off again when I switch the lens to manual (well, or probably it's simply not working at all on manual mode?).

I read in another of your posts that A and M mode are controlled on two circuits and that you had to exchange the capacitors of your prisma. I guess, dried-up or maybe dead Tantalums might be a good starting point.. Do you still know the ratings: voltage and farads (pf or uf)? Or do you even have the schemetics of the prism?
04-17-2012, 10:29 PM   #4
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QuoteOriginally posted by bienemaya Quote
... I found out that I can turn it off again when I switch the lens to manual...
Yes, the two sided circuit would mean the when you flip it to MAN, the AUTO circuit is interrupted. You should check to see if the MAN mode is full working by leaving the lens set and turning ON the meter and watching for it to shutdown in about 30 seconds.

QuoteOriginally posted by bienemaya Quote
it only switches on with a lens mounted.
When the lens is off the aperture lever on the body has returned to the out of range state and so your meter is ON, but the aperture is nolonger giving a return voltage to move meter.

QuoteOriginally posted by bienemaya Quote
Do you still know the ratings: voltage and farads (pf or uf)?
You'll need .47uf and 2.2uf and check the big resistor as well... 3.8K?

04-17-2012, 11:06 PM   #5
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Thanks a lot MysteryOnion!

QuoteOriginally posted by MysteryOnion Quote
Yes, the two sided circuit would mean the when you flip it to MAN, the AUTO circuit is interrupted. You should check to see if the MAN mode is full working by leaving the lens set and turning ON the meter and watching for it to shutdown in about 30 seconds.
It doesn't work properly on MAN. I can't turn it on when on Manual. But it sometimes somehow stays turned on, when I switch between the modes and I do not switch until the lever snaps properly into place. Does this make sense..? I don't know...


QuoteOriginally posted by MysteryOnion Quote
You'll need .47uf and 2.2uf and check the big resistor as well... 3.8K?
Thanks a lot. I will test the components as soon as I'm back home. Unfortunately this will have to wait a little, since I'm "on the road" right now and don't have proper equipment at hand.
04-18-2012, 06:03 AM   #6
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Although you might have already done all this, I thought I should include this anyway about testing the TTL-Prism.

Lens off test: While lens is off, insert the TTL-prism. In this current condition, you are in AUTO still. Now turn on the TTL-prism and then operate the metal lever located in the top flange space while looking through viewfinder for signs of life. To shift into MAN, you only need to press the small pin, located in the center of the lens release pin, down.
04-23-2012, 07:58 AM   #7
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just one more question:
How did you remove the shutter speed dial? I'm trying to open the pentaprism, but somehow can't figure this out.
04-23-2012, 08:47 AM   #8
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It is a screw dead center on it... need a two pin driver of some sort.

Also, carefully work on the locking tabs (bit that latch the prism to the body), they are spring loaded and shoot out if you are too quick removing screws.

A side note, the manner that the meter is switched on is by some sort of Darlington Transistor switch... Voltage goes in to an area that powers the meter, charges a small capacitor, and causes a transistor to continue to leave current running until the capacitor completely discharges... about 30 seconds.


Last edited by MysteryOnion; 04-23-2012 at 08:53 AM.
04-23-2012, 12:24 PM   #9
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Thanks for the last reply.

Managed to remove the two locking tabs (shutter speed dial & the ON/OFF switch of the light meter).
Still it doesn't fall apart.
There are two screws, or at least they look like screws, on the underside near the front (where the Pentax logo is, or rather where the pin is located that hooks into the chain). They have a hole in the middle and a recession that looks as if they needed some kind of very thin minus-shaped screwdriver. Do these two things have to be removed too in order to get access to the electronics inside? Or are there any kind of plastic hooks that snap into place when the plastic housing is put together and which now keep it together? I don't want to break anything so I haven't tried applying more force.
04-24-2012, 06:06 AM   #10
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You're right! Under the name plate are two tiny screws, sorry I forgot about that.

The shell may be tight and a good trick if the prism side of the housing is too resistant. Take a paper clip or stiff wire and bend about 3 to 4 millimeters and press tight to make a narrow hook. Slip the hook up the post holes of the prism and grab the inner edge to give extra leverage to separate, but take your time. Some shells are very snug and coaxing back and forth is needed.

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