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01-07-2015, 12:06 PM   #1
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Spotmatic SP Meter not responding

I bought this Spotmatic over a year ago, but just a couple days ago finally found a battery that's supposed to work. Except it doesn't. The meter, that is. So I'm just checking in here, making sure I'm doing everything right.

I don't have the camera with me, but I think the battery I bought was a 95. It fit well, and I'm pretty sure I got it oriented properly.

So to activate the meter I push up the switch on the left side of the lens mount, right? It clicks into place. There is no response from the meter. The needle stays in a position just a bit below the - indicator.

So if that's the way it's supposed to go, I'm wondering if there's any obvious DIY I can do to wake up the meter. I've repaired cameras, most recently a Nikon FE - I had to swap out the top plate because the original was severely damaged. So I'm not afraid of opening things up and poking around. Does the Spotmatic meter cell just go bad after a while? I guess it does, considering how old these cameras are now.

If I can't get the meter working, it's no big deal. The shutter speeds sound close, at least the slow ones do. And I've got a few light meters, including a Pentax spot meter.

So, any advice? Try to fix it or just use it as it is?

01-07-2015, 12:09 PM   #2
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These are the batteries that work Amazon.com: pentax spotmatic battery
01-07-2015, 12:56 PM   #3
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There are lots of threads on PF about options of batteries you can use for the spotmatics. People say they are quite forgiving in voltage differences. My optically perfect Spotmatic II came with a non-working meter. Since all contacts were clean (corrosion might be easy to fix by unscrewing the bottom plate) i tried to get the meter fixed but was told in several quality repair stores that some of the meter components weren't available any more. Of course you could cannibalize a working Spottie (if you don't run into moral hazards...). Check your repairmen or just enjoy your Spottie with external light meters or the sunny 16 rule (check this out exposure calculator - works great for me).
01-07-2015, 01:44 PM   #4
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Thanks for the prompt responses, guys. Yeah, I had found these lists of substitutes. In fact, I took a long list with me when I went to the battery store. Their computer claimed they had two 387s, which are direct 1.5v replacement, but when I got there they couldn't find them. So out came the list. I think it was the last one on the list where I finally got lucky. I'm on my phone right now, away from the house, so I can't say exactly what I wound up with, but it is silver oxide, so it should be good.

Geedee, I've got a print out of that chart around here somewhere. You're right, it's very useful. I have another that's also good, just text descriptions of scenes that allows you to nail exposure. I've got both tucked away in camera bags somewhere. We just moved into a new house so everything's still disorganized. I know where most of my camera gear is and guitars are. You know, the important stuff. But the camera bags are just in as big pile right now. Heh, that's probably worthy of a thread itself: how many camera bags and cases do we own. And how many of them do we use.

01-07-2015, 02:58 PM   #5
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Check the contacts. A couple of my spotmatics were not working. After I cleaned the contacts they came back to life.
01-07-2015, 05:14 PM   #6
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You know I just got home a little while ago, and that was the first thing I was gonna do. I remember looking at the contacts and thinking they looked good enough, but I'd forgotten how things that looked "good enough" often were anything but in the past. Well the positive blade looked good, but the cap, which is the - node, definitely looked like it had some scale on its interior, so I burnished it well and proper, then sealed it back up. And whaddya know, the meter works! Now, I noticed that the needle was touchy whenever I moved the shutter speed dial. Reminds me of the old stereos or amps with genuine knobs that, if they sat too long, they'd get dust in their pots and when you'd turn them you'd hear the scratchiness. I found the best way to get rid of this, short of tearing into the system and spraying cleaner into the pots, was just to move them back and forth a bunch -- in effect, wiping a clean track back into the resistor path. This was often an easy-does-it process, though. I didn't want to wipe scratches into the resistor path, either. So I did the same thing with the shutter dial, just cranked it back and forth from high to low speeds several times and that seems to have taken care of the jumpiness of the needle.

Now I have a function question. For correct exposure, the meter needle is centered in an opening between the viewing area and a slot next to the viewing area. This opening is wide enough such that, when the needle is deflected either to the top or the bottom of this opening, about 1/2 stop of correction is dialed in. But the slot itself extends quite a ways farther up and down. Just pointing my camera at my computer screen, at ISO 100, it seems to me that this slot shows about 1.5 stops of over exposure and about 2 stops of under exposure. That is, the needle peaks at about 1.5 stops to the plus side and about 2 stops to the minus side. Now, I'm guessing that it's supposed to be even and that it should represent 2 stops over or under, either way. But what I'm noticing is my Spotmatic's meter is much more sensitive to increased light than it is to decreased light. The needle moves rapidly upward with increased light, but quite leisurely downward with decreased light. Is this behavior typical for an "old" Spotmatic meter, or . . . ? And do you happen to know how much over and under this slot is supposed to represent?
01-07-2015, 06:19 PM   #7
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the spotmatic meter is a is a very simple balanced bridge circuit, its cleverly designed in that it maintains a correct (centered meter) exposure reading independent of the battery voltage, however when the battery voltage is incorrect it effects how the meter behaves at it extremes, ( or it's linearity away from the center point ) so if not using the correct 1.35V battery you could expect the response to be non-linear.

QuoteOriginally posted by cooltouch Quote
So to activate the meter I push up the switch on the left side of the lens mount, right? It clicks into place.
there is no switch for the light meter it is activated by light when you take the lens cap off ( or if you put the lens cap on there is next to no current drain from the battery) the switch you refer to on the side next to the lens mount is the depth of field preview switch for the automatic aperture system.
below is a link to some Pentax service manuals which includes the Spotmatic F light meter including how to make adjustments - personally I wouldn't touch it, just be aware that the response is a little non-linear due to the different terminal voltage of the substitute battery, it was only ever designed to give the correct average exposure and maintain accuracy as the battery aged.

Pentax Manuals

the difference in response time for increasing or decreasing light is just the characteristics of the photocell I would think. Also be aware the the meter has limited range, long exposure times with the lens stopped fully down certainly tests the limits of my spotmatic f metering, I'm not sure if this has to do with battery voltage or whether It would do better with the correct battery.
cheers

Last edited by Cee Cee; 01-07-2015 at 06:45 PM.
01-07-2015, 07:00 PM - 2 Likes   #8
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Spotmatic Battery Information

The most experienced members of the Spotmatic group have compiled the information below and many of them have been using Spotmatics since they purchased them brand new in the sixties and seventies. This information is being provided so that you do not have to ask about it as a discussion topic on the forum.

In relation to batteries, there are 5 groups of Spotmatic cameras:
1. SP Series. This includes SP, SP500, SP1000, SPII and SPIIA.
2. SP F
3. Electro Spotmatic and ES
4. ESII.
5. SL. This camera has no meter and, thus, no battery.

SP Series
The 1.35-volt mercury (mercuric oxide) battery originally used in the Spotmatic SP is no longer available due to environmental protection laws.
Replacement batteries available today are 1.55-volt but the Spotmatic uses a "bridge" circuit in its meter, making it insensitive to battery voltage variations. So, despite what you may have read - No meter recalibration is necessary as all Spotmatic SP series cameras can handle the increased voltage.

The alternatives are:
• Spend about $30 for an adapter from CRIS Camera Services (http://www.criscam.com/) and a battery to insert into it. But this would be a waste of money as it is definitely not required.
• Spend about $10 for a Wein Products MRB400 cell (modified Zinc-Air cell). They are quite expensive and have a limited life (about 6 to 12 months) unless you remove the battery after each use and seal up its air hole (it needs air to work). This is not a recommended solution.
• Spend about $3.00 for one of the many 1.55-volt silver oxide batteries available over the Internet, at Radio Shack, most drugstores, camera stores and even some supermarkets. They will last you for about three years if our experience is typical. Make sure you insert it the right way for proper polarity, and take up the excess space in the battery box with a rubber O-ring from the hardware store, that will cost you about 49 cents. You might have to bend up the battery contact in the battery box to make good contact.
• Silver oxide batteries that work are: Mallory PX-400 or RM-400-R, Varta V394, Maxell SR936W or SR936SW, Renata 394, or any type 392 equivalent.
• Do not be tempted to use alkaline battery equivalents as they have a much steeper discharge curve. The silver oxide batteries have a flat discharge curve similar to the old mercury batteries.



SP F.
• Mallory PX625, Duracell PX625A, Excel Z625PX, Eveready E-625N.
• The Spotmatic F uses a dual coil meter movement that, like the bridge circuit, cancels out battery voltage variations on the level we are dealing with here. So it is immune to the difference between 1.35v and 1.5v, too. The original battery for the Spot F was a mercury type. In this case, Pentax used the identical circuit in the KM and K1000, without any electronic changes. They substituted the silver types with NO ALTERATION at all.

Electro Spotmatic and ES.
6-volt Eveready #544, Duracell 28L Lithium.


ESII.
Eveready S76E, Mallory MS-76H, in fact any 76-type battery works -A76, S76, MS76.

Places on the Internet to purchase from:

photobattery.com - photo battery Resources and Information. This website is for sale!
Batteries Plus Bulbs and Battery Store ? Find Battery for laptop, auto, cell phone, SLA, and more - light bulb and LED - Recycling and Sales (good model search facility)
Swatch Battery.com Swatch batteries, watch batteries Watch Battery Renata Energizer (very cheap, good quality)
Right Battery | Right Price | Right Now - MDBattery.com (you need to know the battery number you want)
Right Battery | Right Price | Right Now - MDBattery.com Look for the S400PX (for SP series) or the S625PX (for SPF) on this page.

01-07-2015, 10:00 PM   #9
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QuoteOriginally posted by Cee Cee Quote
the spotmatic meter is a is a very simple balanced bridge circuit, its cleverly designed in that it maintains a correct (centered meter) exposure reading independent of the battery voltage, however when the battery voltage is incorrect it effects how the meter behaves at it extremes, ( or it's linearity away from the center point ) so if not using the correct 1.35V battery you could expect the response to be non-linear.


there is no switch for the light meter it is activated by light when you take the lens cap off ( or if you put the lens cap on there is next to no current drain from the battery) the switch you refer to on the side next to the lens mount is the depth of field preview switch for the automatic aperture system.
below is a link to some Pentax service manuals which includes the Spotmatic F light meter including how to make adjustments - personally I wouldn't touch it, just be aware that the response is a little non-linear due to the different terminal voltage of the substitute battery, it was only ever designed to give the correct average exposure and maintain accuracy as the battery aged.

Pentax Manuals

the difference in response time for increasing or decreasing light is just the characteristics of the photocell I would think. Also be aware the the meter has limited range, long exposure times with the lens stopped fully down certainly tests the limits of my spotmatic f metering, I'm not sure if this has to do with battery voltage or whether It would do better with the correct battery.
cheers
Are you sure re: the metering method on the Spotmatic. I only question your comment as I have read the SW switch is needed to turn the light meter circuit on. My spottie copies need the switch to be activated and yes, as you say, it activates the automatic aperture system. When the shutter releases the SW switch moves into an off position thus turning the circuit off. When the SW switch is in the off position you have a fully manual camera. Anyawy happy to be told otherwise, and if so, then my spottie's are in need of some TLC.
01-07-2015, 10:57 PM   #10
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QuoteOriginally posted by Wild Mark Quote
Are you sure re: the metering method on the Spotmatic. I only question your comment as I have read the SW switch is needed to turn the light meter circuit on. My spottie copies need the switch to be activated and yes, as you say, it activates the automatic aperture system. When the shutter releases the SW switch moves into an off position thus turning the circuit off. When the SW switch is in the off position you have a fully manual camera. Anyawy happy to be told otherwise, and if so, then my spottie's are in need of some TLC.
sorry I've probably thrown a spanner in the works in not being familiar with the differences between models, re-reading the spotmatic F manual it states that one of the improvements over previous models is that "the metering system is now activated simply by removing the lens cap." I should have read the OP comments a bit more carefully as he says he has a Spotmatic not a Spotmatic F.
BTW my comments relating to battery voltage stem from testing metering operation while running from a variable voltage power supply, and noting that correct exposure reading didn't change much at all when voltage was varied from 1.2V to 1.6V but at a stop or two high or low it seemed to make some difference. I think the circuits are all pretty similar so I would expect that behavior to be the same, others may find differently.
cheers
01-08-2015, 09:36 AM   #11
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Yeah, I have to agree with Wild Mark. My SP requires that switch to be moved upward to activate the meter. I've been aware of the Pentax bridge circuit for years, often bemoaning the fact that (as a Canon user) Canon had not seen fit to incorporate a similar circuit in their meter designs.

Thanks for forwarding the Spottie battery info, Ray, but I've already read all this more than once. My original questions had nothing to do with batteries, but rather how to get the meter to respond. Subsequent questions were about the meter readout.

Incidentally, y'all might want to add the 1.55v silver-oxide Renata 395 to your list of compatible batteries as a replacement for the 1.35v PX400. I ran across this one as being a workable substitute somewhere on the 'net, and it was my last straw at the battery store. It fits fine, requiring no o-ring or bit of wire as a centering spacer. But, man-o-man, did I get overcharged! I think I paid about 7 bucks for it, and I'm seeing 'net prices for it to be around a dollar.
01-08-2015, 10:11 AM - 1 Like   #12
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- Clean battery contacts, use a pencil eraser to "rub" any oxide
- Make sure there is contact, you can pry the little tab up a very carefully
- Camera set speed to B, ASA to 100 and the flick the lightmeter switch... it should drop like a rock (if it goes up your battery is backwards)
01-08-2015, 11:16 AM   #13
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QuoteOriginally posted by cooltouch Quote
The needle moves rapidly upward with increased light
I see this on my SPF too, which is not reliable in bright sunlight. Anything up to moderate sun is correctly metered but as soon as you get a bright day and the sun starts to creep into the edge of the shot the needle is still into the + area at f16, 1/1000 at ISO100, which led to a few heavily underexposed shots back when I was inexperienced. Whether this was always a problem or if it's an age thing I don't know, but it's good to know I'm not the only one who's noticed this.
01-08-2015, 12:37 PM   #14
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QuoteOriginally posted by titrisol Quote
- Clean battery contacts, use a pencil eraser to "rub" any oxide
Or if the only thing you have handy is the dime you used to open up the battery compartment, just scrape it across the underside of the cap several times. The prong (+) was in good shape.

QuoteQuote:
- Camera set speed to B, ASA to 100 and the flick the lightmeter switch... it should drop like a rock (if it goes up your battery is backwards)
Now, it's little tips and tricks like this that I like finding out about. Yep, the needle dropped like a hot rock.
01-08-2015, 04:37 PM   #15
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It's in the manual.... you can find a good copy at
PENTAX MANUALS

QuoteOriginally posted by cooltouch Quote

Now, it's little tips and tricks like this that I like finding out about. Yep, the needle dropped like a hot rock.
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