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04-15-2010, 02:51 PM   #1
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Has anyone here worked on a KX meter?

I was just given a KX, mechanically okay at first glance, but with a bad meter. The battery check button does nothing. My first thought was, oh, this will be easy -- it'll be a connection near the battery. But no, I can trace the 3v supply up to the little switch by the shutter button, and from there (once the advance lever is at standoff and the shutter half-pressed) to a board on top of the pentaprism and another board under the ISO adjustment knob. So there's juice in the right places, roughly speaking. But the needle is always pegged at the top.

There don't seem to be schematics readily available for this unless someone here has one; also from what I've read it doesn't share its meter circuit with any other camera, so stealing bits from a parts body isn't an option.

Any help, short of sending it off to El Hombre? I might end up willing to do that, as he's done good work for me before; but I'd like to try my hand at this one, both for economy and pride.

04-15-2010, 03:01 PM   #2
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QuoteOriginally posted by Sluggo Quote
I was just given a KX, mechanically okay at first glance, but with a bad meter. The battery check button does nothing. My first thought was, oh, this will be easy -- it'll be a connection near the battery. But no, I can trace the 3v supply up to the little switch by the shutter button, and from there (once the advance lever is at standoff and the shutter half-pressed) to a board on top of the pentaprism and another board under the ISO adjustment knob. So there's juice in the right places, roughly speaking. But the needle is always pegged at the top.

There don't seem to be schematics readily available for this unless someone here has one; also from what I've read it doesn't share its meter circuit with any other camera, so stealing bits from a parts body isn't an option.

Any help, short of sending it off to El Hombre? I might end up willing to do that, as he's done good work for me before; but I'd like to try my hand at this one, both for economy and pride.
Not a KX, but those seem very similar to Canon FTbs in metering. A short somewhere can account for this, or reversed polarities somewhere along the line, (make sure your batteries are in right and no previous work did that, if you come down to that,) and this will sometimes happen if there's a fault in the metering cell. It's best to troubleshoot by being careful to check everything along the way before you get into the more delicate parts.

The fact that the check button does nothing (I'm not sure how those display on a KX) may mean it's actually stuck in an open position, (by the needle swinging all the way up, perchance? ) meaning whatever happens, the camera's checking battery. That might be the first thing I'd look at: it's probably the most fixable thing for you anyway.

Also, if you take anything apart near the meter, remember that through the finder, your view may be a mirror image of the actual components as you see them directly. *sheepish darting of the eyes,* ....maybe I've been there, maybe I haven't


Anyway, that may or may not be helpful. I'm afraid I don't have any insider tips. But of course, Eric has em all.
04-15-2010, 03:19 PM   #3
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Another vote for checking battery polarity. If it's backwards, the meter's trying to swing the meter the wrong way (up in the viewfinder)--and it's not gonna do that too well!
04-15-2010, 03:52 PM   #4
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QuoteOriginally posted by Stevopedia Quote
Another vote for checking battery polarity.
Thanks, but the polarity is clearly marked on the battery cap, and I had it right. Of course after being prompted here, I tried turning the cells around backwards once for the hell of it too!

It's a long shot, but I'm still hoping somebody will pipe up with "oh, I happen to have that schematic" or "resistor thus-and-so commonly needs to be replaced" or something like that. Not that I mind people pointing out the obvious stuff too, because you're right, it's easy to overlook the possibility of user errors.

The bad meter was the reason the camera was free, so I've got nothing to complain about.

04-15-2010, 04:59 PM   #5
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Is it possible you've got a stuck needle? If you've verified the electronics are OK, I would suspect the needle itself.
04-15-2010, 05:27 PM   #6
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VF-19 has a good point, I was imagining you said it would always swing to the top when there was power. Sometimes they really do just get physically-stuck. Gentle persuasion can work just fine there, if that's all that's wrong.
04-15-2010, 05:57 PM   #7
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Mine sometimes has a problem with the mechanical lens mount linkages... I need to un and re mount the lens, that tends to fix it. The symptom of this is the meter won't meter.
04-16-2010, 08:27 AM   #8
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I had my KX meter fixed by a local shop in 1994 after someone had hit the top of the prism housing causing the needle to just flop around.

Depending on where you are there should be a competant pentax repair person nearby that can fix the camera. the issue will be parts.

04-16-2010, 10:57 AM   #9
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The needle seems neither frozen nor floppy; it quivers a little when you tap the camera body, as you'd expect if it was mechanically good but getting no signal. I haven't verified the electronics are okay, just that the 3v power supply is making it to the circuit boards involved in metering. So I'm still leaning toward an electrical fault of some kind.

Nesster, I remember my MX when I first got it was something like you describe. The aperture linkage arm in the body would get stuck in place and it made the meter useless. The repair: a judicious tweak with needle-nose pliers, and it's been happy ever since. Apparently it had been sticky because it was bent. Not so with this KX - the arm moves consistently, though it's a little stiff.

Lowell, I don't think I have anybody local - if I do end up sending this to a pro, it will be Eric H, who did a great job reconditioning a Spotmatic for me recently.
04-16-2010, 11:22 AM   #10
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Hrm, ...should the meter travel when there's no lens mounted at all, but you check to see if it responds to light?

And does it ever move away from there in general, or is it just always there doing the same thing whether there is power or not, Sluggo?
04-16-2010, 11:34 AM   #11
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RML, it doesn't seem to respond to light or electricity at all. Or to the battery-test button, which is supposed to always swing the needle down.

But ... thinking about that "gentle persuasion" comment, I just gave the camera more of a shake, and now the meter will float in any arbitrary position. Shake it again, it changes to another reading.

So yeah, it looks like a mechanical problem after all. :-/

Edit: or maybe it's both, now ... hrmmmmm.

Last edited by Sluggo; 04-16-2010 at 11:41 AM. Reason: afterthought
04-16-2010, 03:32 PM   #12
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QuoteOriginally posted by Sluggo Quote
RML, it doesn't seem to respond to light or electricity at all. Or to the battery-test button, which is supposed to always swing the needle down.

But ... thinking about that "gentle persuasion" comment, I just gave the camera more of a shake, and now the meter will float in any arbitrary position. Shake it again, it changes to another reading.

So yeah, it looks like a mechanical problem after all. :-/

Edit: or maybe it's both, now ... hrmmmmm.
Hey, that could be good news and bad news. If you're already in there, both seat the needle on whatever drives it, and be sure it encounters no resistance. (check how it's seated, first, before trying to bend. It may have been bent by the original fault in the first place, or possibly not. I'd offer to try it if my fingers were quite what they once were (And I still had good tools) Bad news is, you might have a dead meter cell.

Or the needle may have just come off its mounting and you just took it unstuck. This is usually delicate, but not complicated to fix, if so. You're safest with Eric on this, though, and I'd suggest that unless you have very fine manual dexterity, it's not worth bending the part to find out. No shame, there. If you do try it, place some card or paper of the right depth underneath where the needle travels. (err on the side of too thin) As I said, I've only worked on analagous Canons, and this would really mean you want some fine control of what you're doing. (I'm not sure I recall, but it'd just be like a teeny (and thin) version of a cheap kitchen clock's hand on a square post. To re-seat it takes just having a touch.

If you bend it out of shape, you're looking for a parts camera, so, bear it in mind. If the needle's off its seat, you don't know much about what what it attaches to does, so tread carefully, and don't be ashamed to send it to Eric. He has the skills and the bench.
04-16-2010, 05:06 PM   #13
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QuoteOriginally posted by ChrisPlatt Quote
35 years on a replacement meter movement for the KX is well nigh impossible to get.
Rather than risk messing up a possibly good one, I advise sending the camera to Eric.

Chris
I've exchanged email with him - if it does need a meter movement (and from the description, he thinks it does), he can get it. Maybe I didn't break anything that didn't need replacing anyway.

Guess I'll mull this over a bit. I don't really need this camera as a shooter, but it's obviously a piece of quality kit. Although I could enjoy putzing around with it some more, it seems a shame if by doing so I render it unrepairable, thereby reducing the world population of viable KX bodies by one.
04-18-2010, 12:41 PM   #14
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linking this, not the same but may be helpful info

Disassembly of the Pentax ME Super Camera

Calibrate the K1000
04-27-2010, 02:52 PM   #15
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Followup

I did finally figure out the decisive point to measure at. When I press the battery test button, there is voltage across the meter movement, but the needle doesn't respond in the least -- nor did it before the "gentle persuasion" attempt. The meter movement is simply kaput.

The camera is now in the mail heading toward Tennessee.
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