6x7 lightmeter not working

smurley · 03-26-2012, 07:18 AM

Batter is fine and shutter is accurate (just made 20 exposures using a hand-held LunaSix F).

No needle movement at all in the prism light-meter. It was working a year ago when I last had it out.

Any ideas for trouble-shooting?

-stm

tuco · 03-26-2012, 07:27 AM

If the chain is not broken, the battery is good and it worked last time you used it, remove the lens and then the metering prism. Try cleaning the contacts where the pins on the prism contact the body. The prism gets its voltage through one of those contacts.

smurley · 03-26-2012, 08:30 AM

Thank you. I'll do that. Maybe put a volt-meter on those contacts?

-stm

MysteryOnion · 03-26-2012, 08:34 AM

If you are testing the contact, the one on the left is the regular contact and the frame is the other end... see below

... the body is the negative for normal operation, so the probe might work best on the latch.

Last edited by MysteryOnion; 03-26-2012 at 04:18 PM.

smurley · 03-26-2012, 03:59 PM

Thanks. I appreciate the info (and pictures alway help)

**gofour3** · 03-26-2012, 04:27 PM - **2 Likes**

It’s a long shot but maybe try this.

I have an intermittent issue with my 67 TTL meter, where is just won’t turn on and it’s happened with various lenses. To get the meter to work again I move the lenses DOF lever to manual and turn “on” the meter. Presto is starts to work? I can then move the DOF lever back to auto and all is well for the rest of the roll.

Not sure what’s going on, according to the TTL manual the meter doesn’t work in the manual setting.

Phil.

tuco · 03-26-2012, 04:30 PM

I think the "negative 6V" pin is really just ground. Your volt meter may read -6V when connected backwards but the potential across the two pins regardless of polarity is 6V.

MysteryOnion · 03-26-2012, 04:53 PM

gofour3... the TTL actually seems to have two meter circuits. The MAN. mode bypasses the aperture and shutter potentiometer (Tv the Av) to a set resistor value... this is stopdown mode. If when you flip from AUTO to MAN to AUTO that it seems to wake it up the meter could mean either the capacitor or the transistor in the turning on circuit is faulty.

smurley... gofour3 makes a good point, maybe half the meter is still working or can help the other half.

I've been studying from my two dirt cheap "as-is" TTL prisms and hope to figure out how to replace the old circuit with a new one.

03-26-2012, 07:18 AM	#1
smurley New Member Join Date: Mar 2012 Posts: 6	6x7 lightmeter not working Batter is fine and shutter is accurate (just made 20 exposures using a hand-held LunaSix F). No needle movement at all in the prism light-meter. It was working a year ago when I last had it out. Any ideas for trouble-shooting? -stm

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03-26-2012, 07:27 AM	#2
tuco Pentaxian Join Date: Jul 2009 Location: Pugetopolis Posts: 11,026	If the chain is not broken, the battery is good and it worked last time you used it, remove the lens and then the metering prism. Try cleaning the contacts where the pins on the prism contact the body. The prism gets its voltage through one of those contacts.

03-26-2012, 08:30 AM	#3
smurley New Member Join Date: Mar 2012 Posts: 6 Original Poster	Thank you. I'll do that. Maybe put a volt-meter on those contacts? -stm

03-26-2012, 08:34 AM	#4
MysteryOnion Giveaway winner! Join Date: Dec 2007 Location: beantown Photos: Albums Posts: 944	If you are testing the contact, the one on the left is the regular contact and the frame is the other end... see below ... the body is the negative for normal operation, so the probe might work best on the latch. Last edited by MysteryOnion; 03-26-2012 at 04:18 PM.

03-26-2012, 03:59 PM	#5
smurley New Member Join Date: Mar 2012 Posts: 6 Original Poster	Thanks. I appreciate the info (and pictures alway help)

03-26-2012, 04:27 PM - 2 Likes	#6
gofour3 Site Supporter Join Date: Oct 2008 Location: Vancouver, Canada Posts: 8,091	It’s a long shot but maybe try this. I have an intermittent issue with my 67 TTL meter, where is just won’t turn on and it’s happened with various lenses. To get the meter to work again I move the lenses DOF lever to manual and turn “on” the meter. Presto is starts to work? I can then move the DOF lever back to auto and all is well for the rest of the roll. Not sure what’s going on, according to the TTL manual the meter doesn’t work in the manual setting. Phil.

03-26-2012, 04:30 PM	#7
tuco Pentaxian Join Date: Jul 2009 Location: Pugetopolis Posts: 11,026	I think the "negative 6V" pin is really just ground. Your volt meter may read -6V when connected backwards but the potential across the two pins regardless of polarity is 6V.

03-26-2012, 04:53 PM	#8
MysteryOnion Giveaway winner! Join Date: Dec 2007 Location: beantown Photos: Albums Posts: 944	gofour3... the TTL actually seems to have two meter circuits. The MAN. mode bypasses the aperture and shutter potentiometer (Tv the Av) to a set resistor value... this is stopdown mode. If when you flip from AUTO to MAN to AUTO that it seems to wake it up the meter could mean either the capacitor or the transistor in the turning on circuit is faulty. smurley... gofour3 makes a good point, maybe half the meter is still working or can help the other half. I've been studying from my two dirt cheap "as-is" TTL prisms and hope to figure out how to replace the old circuit with a new one.