Does anyone have a dead Pentax Spotmatic?

Strapps

Strapps

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Dean
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@stevelmx5 very kindly gave me a Pentax SP at the mega-meet with a warning that the meter appeared to read backwards. I did some googling earlier and there was a chance that this was caused by the battery being installed the wrong way around. A quick meter test indicated that all was well with the electrics and it certainly looked as though the meter was indicating the wrong way to adjust exposure.

I removed the battery cap and found a small watch battery held in place with blue tac and a couple of bits of foil; sure enough it was upside down. Chuffed at a potential easy fix, I took the battery out, only to find that the spring tab at the bottom of the battery bay came with it. Guess it'd succumbed to fatigue after having been bent up previously to accept smaller-than-standard batteries.

I've tried repacking it in various ways but without success, hence the question of this topic. Does anyone have a deceased SP that I can rob the base plate from, please? It should be a straightforward swap and in the meantime I can at least play with the camera on manual as the shutter sounds accurate.

The seals are all quite sticky so they'll need doing as well but one thing at a time :)
 
Nooooo! Sorry about that Dean. The battery was fitted like that when I got it and appeared to be functioning (although backwards) so I'd never bothered to investigate further and it's sat in my camera bag for the last 12 months at least.
 
No worries Steve, it's a lovely camera and has come up a treat with a wipe and a dab of lighter fluid. The shutter speed dial is light enough to roll around with one finger, an issue I had with my ST801 that put me off using it. It's worth running a film through on manual with a separate meter as a test.

Thanks again :)
 
Apart from the over and under directions of the meter being wrong, it will still show correct exposure with the cell in the wrong way round.


Steve.
 
Steve Smith said:
Apart from the over and under directions of the meter being wrong, it will still show correct exposure with the cell in the wrong way round.
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Yes but if the fix is as simple as turning the battery over, wouldn't you have tried it? Academic now, of course. :)
 
Strappy said:
Yes but if the fix is as simple as turning the battery over, wouldn't you have tried it? Academic now, of course.
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There are some cells which fit better upside down. Normally, you need to put a rubber O ring around it to stop the sides from shorting out to the screw in holder but if it's upside down, it doesn't matter as the side connects to the body anyway.

But yes, I would!

I might have a junk one here. I will have a look when I get home. I have some 1mm black self adhesive foam too if you want some of that for the seals.


Steve.
 
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Steve Smith said:
There are some cells which fit better upside down. Normally, you need to put a rubber O ring around it to stop the sides from shorting out to the screw in holder but if it's upside down, it doesn't matter as the side connects to the body anyway.
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Absolutely and I think that's the reason why it was upside down in the first place; it looks right due to the shape of the battery chamber. The original battery was a mercury PX400 that had a sort of collar around it and the replacement, the 387s, had a plastic collar. Unfortunately it seems the 387s is no longer made either but I have a selection of rubber o-rings to try on smaller replacements.

Good thing about the Spotmatic is that all models have voltage regulating hardware built in so a 1.5v cell isn't going to affect the meter reading.

Steve Smith said:
I might have a junk one here. I will have a look when I get home. I have some 1mm black self adhesive foam too if you want some of that for the seals.
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Thanks, that'd be great :)
 
Strappy said:
Good thing about the Spotmatic is that all models have voltage regulating hardware built in so a 1.5v cell isn't going to affect the meter reading.
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There is no voltage regulation circuit. It works with any cell because correct exposure is shown when no current flows through the meter in either direction. The only difference which might be visible is that with a 1.5v cell, over and under exposure positions of the needle will be slightly greater than with the 1.35v mercury cell.


Steve.
 
I sit corrected :)

I was quoting information I read from various sources (sample link) that there was a 'bridge' circuit that regulated the voltage.
 
Thanks, Brian, but it's not the voltage that's the problem. The issue is that the battery chamber is shaped in such a way that many of the more common batteries simply don't fit.
 
Strappy said:
I was quoting information I read from various sources (sample link) that there was a 'bridge' circuit that regulated the voltage.
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There is indeed a bridge circuit. But that doesn't regulate. It just passes current through the meter when there is a difference between the two sides. When they are equal, no current flows. This is the point of correct exposure.

When no current flows, it doesn't matter what the source voltage is as x - x = 0

http://www.electronics-tutorials.ws/blog/wheatstone-bridge.html


Steve.
 
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Progress! I cut to the chase of fiddling with different batteries and bits of foil and blu-tac and ordered an S400PX from the Small Battery Company, which is a direct replacement for the older mercury battery in size if not voltage. It's a 392 watch cell (1.55v) with a plastic collar that fits into the battery chamber exactly but is also £3.50 more expensive than plain 392 batteries.

The battery doesn't reach the positive terminal at the bottom of the chamber due to the tapered shape. This is obviously why there's a folding tab for that terminal but that's the bit which broke on my camera. I considered trying to solder the tab in place but the soldering iron is in the garage and I wanted to make sure the meter is ok so instead I've put a nub of foil on the battery and held it in place with tape, with a hole cut though the centre to ensure it won't short out on the side of the battery chamber.

Long story short, it appears to be working correctly, the battery check works as per the Pentax manual and the meter reading matches my digital camera (or at least is close enough). It's enough to run a film through for checking the light seals.

One strange thing, when I removed the base plate to check for corrosion on the contact to the battery chamber, a small spring fell out. It wasn't connected to anything and I can't see anywhere it would fit. I've looked at pictures of other Spotmatics online and there's no indication of that spring anywhere. Nothing seems to have stopped working so I've left it out for now, would be interested if anyone has any ideas :)

A couple of pics ... the spring in question is on the body cap to give an idea of its size.


Spotmatic-1 by Strappy, on Flickr

Cleaned up and fitted with the cheap Takumar I purchased from Rocky a couple of weeks ago. Roll of testing film not yet loaded.


Spotmatic-3 by Strappy, on Flickr
 
That bit of wire under the screw looks crude , h'mm look on the net and it does look like that :eek:
 
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That Takumar 55mm f/1.8 was the lens on my first SLR also a Spotty! Nice. I was a bit disappointed when the ME had a 50mm!
 
excalibur2 said:
That bit of wire under the screw looks crude , h'mm look on the net and it does look like that :eek:
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It does look like an unfolded paperclip, doesn't it :D

It's the mirror restitution spring according to the service manual I downloaded; if the mirror doesn't come down but the shutter still works, it's probably slipped out of the hole at the end of that little lever (the mirror actuation lever bottom, apparently). Good thing to know if you find a 'broken' Spotmatic at the booty, Brian ;)
 
fyi on my spotmatic the shutterspeeds are acurate apart from 1/1000 which is actually 1/4000 and abit of curtain
 
Strappy said:
@stevelmx5Does anyone have a deceased SP that I can rob the base plate from, please?
Click to expand...

Steve Smith said:
I might have a junk one here. I will have a look when I get home. I have some 1mm black self adhesive foam too if you want some of that for the seals.
Click to expand...

Sorry for the delay (Isle of Wight Festival kept me busy).

I do have a junk one here if you want it for spares. Or I could just post the base plate to you (cheaper postage).

This one had its mirror stuck in the up position. Strangely, it has now decided to start working properly but I won't trust it to stay that way.

The actual screw fit cell cover is very chewed up by years of beaing removed by the wrong tool but the baseplate is o.k. if a bit scratched.

Let me know if you want it.


Steve.
 
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Thanks, Steve :)

I only need the baseplate but a friend wants to try using camera internals to make steampunk brooches so if it's a junker that you have no use for, I'll take the whole camera, please, and will forward the remains to her. As long as the folded tab in the bottom of the battery compartment is in one piece, it's in better shape than the one I have here!

I'll PM you about the details.
 
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