Pentax LX mirror stuck up in AUTO only

geauxpez · 08-18-2010, 04:40 AM

I just spent time over the weekend testing my LX before I packaged it for its new home in Oz. Partly because I just love that advance lever.

When I advanced & tripped the shutter with a body cap on (no film), the shutter "stuck" open because of the lack of light hitting the meter at the time of exposure. When I took the body cap off (after re-setting the camera by turning to manual mode), everything worked fine (again, no film) while advancing the lever and firing.

Wheatfield · 08-18-2010, 10:29 AM

People, in auto the LX meters OFF THE FILM.
It's the way it works.
With no film in the camera, the metering if off the pressure plate which is pretty non reflective.

In Auto with no film in the camera, the LX will hold the shutter open pretty much until the battery dies or electronic noise fools it into thinking it's made the exposure.

This is not a feature, nor is it a fault, it is a function of the camera design.

The LX will appear to meter properly with no film in the camera because it is metering off the shutter curtain until the shutter button is pressed, but it will not expose properly in auto until film is in the camera.
Post 14 of this thread is dead wrong.

Edit: Also, the LX may not work right with a 357 battery. I know none of mine do (I have 3). Get a set of fresh S-76 batteries and try them before you send your camera back.

**carlb** · 08-18-2010, 03:06 PM

Originally posted by Wheatfield

Edit: Also, the LX may not work right with a 357 battery. I know none of mine do (I have 3). Get a set of fresh S-76 batteries and try them before you send your camera back.

Why is this? Could you please elaborate. And how can I check? Thanks

iht · 08-18-2010, 03:39 PM

Quote:

The LX will appear to meter properly with no film in the camera because it is metering off the shutter curtain until the shutter button is pressed, but it will not expose properly in auto until film is in the camera.
Post 14 of this thread is dead wrong.

LX owners, why don't we all conduct an experiment? Set your LX with batteries to AUTO, remove film, set your lens to f1.4, ASA to 800, and stand about a metre from a 100W lightbulb and shoot straight at it. The point is: you're shooting at something bright. Does the instant mirror return in yours? It's not supposed to be something conclusive, but just out of interest.

Quote:

Also, the LX may not work right with a 357 battery. I know none of mine do (I have 3). Get a set of fresh S-76 batteries and try them before you send your camera back

Thanks for the suggestion. That's interesting as well. As mentioned, I had already returned the camera. FYI, all shutter speeds (including the lower ones) worked - only AUTO didn't.

Last edited by iht; 08-18-2010 at 03:57 PM.

Wheatfield · 08-18-2010, 09:52 PM

The LX effectively has 2 metering circuits operating. One is what you see in the viefinder and is generated by light coming in the lens and being reflected off a sub mirror and down to the meter cell.
The second one is pretty much independent of the first, though it uses the same hardware.
In manual, you meter off the primary circuit and set your exposure.
In auto what you see in the viewfinder is the same as what you see in manual (with the exception of the chase LED). When you push the button, the mirror flips out of the way and the camera takes a meter reading off the pattern on the shutter curtain and sets it's exposure accordingly.
Then, when the shutter opens, the meter continues to take a reading off the film itself and continues the exposure until the meter says there has been enough, at which time the shutter closes.
Because the pressure plate has effectively zero reflectivity compared to film, the camera simply cannot give an accurate exposure in auto unless film is in the camera.
357 batteries don't have the same milliamp hour output, and so may not supply what the camera needs in any given situation.

However, the LX does have some issues. One is the aperture cam follower resistor which is prone to corrosion, as is the ISO resistor. Later cameras were fixed with resistors that were wound with gold thread, but a cheap and easy temporary fix is to rotate both the ISO dial and/or the aperture cam follower several times to clean them.
The LX is also prone to sticky mirror. Generally this manifests by the mirror hanging for a moment the first time the shutter button is pushed after the camera sits idle for a while.
It may also be noted that the focus plane is not the same from top to bottom of the screen. This is caused by the rubber bumper on the mirror rest literally dissolving and allowing the mirror to sit at rest out of alignment.
The only time I've seen an LX mirror not drop immediately after exposure, it was caused by the foam bumper at the top of the mirror box dissolving unto goo and literally sticking the mirror to the focus screen area.
A good repair shop will replace every rubber bumper, foam and pad in the mirror box as part of a CLA.
If your mirror is hanging after exposure (after the shutter closes), then the camera needs a bit more work done to it.

iht · 08-19-2010, 12:40 AM

Wheatfield, thanks for the very detailed info. Very interesting.

Cheers again to everyone for your contribution! I do hope I'll get my working LX very soon...

kcw · 08-19-2010, 01:00 AM

Quote:

Also, the LX may not work right with a 357 battery. I know none of mine do (I have 3). Get a set of fresh S-76 batteries and try them before you send your camera back.

Maybe you can ask your repair guy on how he tested the camera before shipment? I would have thought the camera should have been returned to you in working condition including batteries. LR44 batteries are cheap. It would have protected both of you as one variable (the batteries) is from the equation. Make sure you ask for that next time, or go with Eric.

**Pål Jensen** · 08-20-2010, 12:16 PM

This is a rather common fault on the LX. After 19 years (in 2000) my LX got the same problem. The repair guy knew what it was when I described it over the phone; it was a switch (or something) that need to be replaced. The symptom is that the camera does not work in automatic; manual works.

Stachu · 08-22-2010, 10:30 AM

I have similar problem with my LX. Camera works on Auto, but mirror stucks on times longer than X. Lightmeter seems to work but not propertly and is always on and meter only with shutter cocked.

iht · 09-13-2010, 03:28 PM

Bad news: electronic issue

systemA · 09-24-2010, 03:03 AM

Same problem here

Mirror stuck after shutter release in AUTO modes and shutter speeds below Xsync. Originally, I had no idea what these symptoms indicated, but was fairly sure it wasn't stick mirror syndrome. What's more unfortunate is that I traded my baby k10d for this LX and don't have funds for a CLA. Tough luck!

AndrewG NY · 09-29-2010, 11:37 AM

I think you're already past this question but my LX will drop the mirror in auto, but I expect the exposure time to be somewhat inaccurate as the meter would have been calibrated for the reflectivity of film rather than that of the pressure plate.

It is my understanding that Pentax may still be capable of servicing LX but I would expect it to be pricey...not sure about availability of specific parts but it would be worth asking as a working LX is pretty valuable. You can also look out for a donor LX, perhaps one with mechanical problems.

I would also consider e-mailing Eric. Even if you don't end up sending it to him it is likely that based on what the other repair guy told you provide some good advice.

I would expect that the camera still works well in manual mode?

08-18-2010, 10:29 AM	#17
Wheatfield Moderator Join Date: Apr 2008 Location: The wheatfields of Canada Posts: 15,981	People, in auto the LX meters OFF THE FILM. It's the way it works. With no film in the camera, the metering if off the pressure plate which is pretty non reflective. In Auto with no film in the camera, the LX will hold the shutter open pretty much until the battery dies or electronic noise fools it into thinking it's made the exposure. This is not a feature, nor is it a fault, it is a function of the camera design. The LX will appear to meter properly with no film in the camera because it is metering off the shutter curtain until the shutter button is pressed, but it will not expose properly in auto until film is in the camera. Post 14 of this thread is dead wrong. Edit: Also, the LX may not work right with a 357 battery. I know none of mine do (I have 3). Get a set of fresh S-76 batteries and try them before you send your camera back. Last edited by Wheatfield; 08-18-2010 at 12:40 PM. Reason: More info

08-19-2010, 12:40 AM	#21
iht Veteran Member Join Date: May 2009 Location: Sydney, Australia Photos: Gallery Posts: 528 Original Poster	Wheatfield, thanks for the very detailed info. Very interesting. Cheers again to everyone for your contribution! I do hope I'll get my working LX very soon... Last edited by iht; 08-19-2010 at 01:10 AM.

09-13-2010, 03:28 PM	#25
iht Veteran Member Join Date: May 2009 Location: Sydney, Australia Photos: Gallery Posts: 528 Original Poster	Bad news: electronic issue Last edited by iht; 10-26-2010 at 05:12 AM.

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08-18-2010, 04:40 AM	#16
geauxpez Veteran Member Join Date: Jul 2008 Location: Atlanta Photos: Gallery Posts: 1,196	I just spent time over the weekend testing my LX before I packaged it for its new home in Oz. Partly because I just love that advance lever. When I advanced & tripped the shutter with a body cap on (no film), the shutter "stuck" open because of the lack of light hitting the meter at the time of exposure. When I took the body cap off (after re-setting the camera by turning to manual mode), everything worked fine (again, no film) while advancing the lever and firing.

08-18-2010, 03:06 PM	#18
carlb Site Supporter Join Date: Jan 2009 Location: Perth, Western Australia Posts: 1,162	Originally posted by Wheatfield Edit: Also, the LX may not work right with a 357 battery. I know none of mine do (I have 3). Get a set of fresh S-76 batteries and try them before you send your camera back. Why is this? Could you please elaborate. And how can I check? Thanks

08-18-2010, 03:39 PM	#19
iht Veteran Member Join Date: May 2009 Location: Sydney, Australia Photos: Gallery Posts: 528 Original Poster	Quote: The LX will appear to meter properly with no film in the camera because it is metering off the shutter curtain until the shutter button is pressed, but it will not expose properly in auto until film is in the camera. Post 14 of this thread is dead wrong. LX owners, why don't we all conduct an experiment? Set your LX with batteries to AUTO, remove film, set your lens to f1.4, ASA to 800, and stand about a metre from a 100W lightbulb and shoot straight at it. The point is: you're shooting at something bright. Does the instant mirror return in yours? It's not supposed to be something conclusive, but just out of interest. Quote: Also, the LX may not work right with a 357 battery. I know none of mine do (I have 3). Get a set of fresh S-76 batteries and try them before you send your camera back Thanks for the suggestion. That's interesting as well. As mentioned, I had already returned the camera. FYI, all shutter speeds (including the lower ones) worked - only AUTO didn't. Last edited by iht; 08-18-2010 at 03:57 PM.

08-18-2010, 09:52 PM	#20
Wheatfield Moderator Join Date: Apr 2008 Location: The wheatfields of Canada Posts: 15,981	The LX effectively has 2 metering circuits operating. One is what you see in the viefinder and is generated by light coming in the lens and being reflected off a sub mirror and down to the meter cell. The second one is pretty much independent of the first, though it uses the same hardware. In manual, you meter off the primary circuit and set your exposure. In auto what you see in the viewfinder is the same as what you see in manual (with the exception of the chase LED). When you push the button, the mirror flips out of the way and the camera takes a meter reading off the pattern on the shutter curtain and sets it's exposure accordingly. Then, when the shutter opens, the meter continues to take a reading off the film itself and continues the exposure until the meter says there has been enough, at which time the shutter closes. Because the pressure plate has effectively zero reflectivity compared to film, the camera simply cannot give an accurate exposure in auto unless film is in the camera. 357 batteries don't have the same milliamp hour output, and so may not supply what the camera needs in any given situation. However, the LX does have some issues. One is the aperture cam follower resistor which is prone to corrosion, as is the ISO resistor. Later cameras were fixed with resistors that were wound with gold thread, but a cheap and easy temporary fix is to rotate both the ISO dial and/or the aperture cam follower several times to clean them. The LX is also prone to sticky mirror. Generally this manifests by the mirror hanging for a moment the first time the shutter button is pushed after the camera sits idle for a while. It may also be noted that the focus plane is not the same from top to bottom of the screen. This is caused by the rubber bumper on the mirror rest literally dissolving and allowing the mirror to sit at rest out of alignment. The only time I've seen an LX mirror not drop immediately after exposure, it was caused by the foam bumper at the top of the mirror box dissolving unto goo and literally sticking the mirror to the focus screen area. A good repair shop will replace every rubber bumper, foam and pad in the mirror box as part of a CLA. If your mirror is hanging after exposure (after the shutter closes), then the camera needs a bit more work done to it.

08-19-2010, 01:00 AM	#22
kcw New Member Join Date: Aug 2010 Posts: 2	Quote: Also, the LX may not work right with a 357 battery. I know none of mine do (I have 3). Get a set of fresh S-76 batteries and try them before you send your camera back. Maybe you can ask your repair guy on how he tested the camera before shipment? I would have thought the camera should have been returned to you in working condition including batteries. LR44 batteries are cheap. It would have protected both of you as one variable (the batteries) is from the equation. Make sure you ask for that next time, or go with Eric.

08-20-2010, 12:16 PM	#23
Pål Jensen Site Supporter Join Date: Dec 2007 Location: Norway Photos: Albums Posts: 4,371	This is a rather common fault on the LX. After 19 years (in 2000) my LX got the same problem. The repair guy knew what it was when I described it over the phone; it was a switch (or something) that need to be replaced. The symptom is that the camera does not work in automatic; manual works.

08-22-2010, 10:30 AM	#24
Stachu Inactive Account Join Date: May 2010 Posts: 1	I have similar problem with my LX. Camera works on Auto, but mirror stucks on times longer than X. Lightmeter seems to work but not propertly and is always on and meter only with shutter cocked.

09-24-2010, 03:03 AM	#26
systemA Veteran Member Join Date: Nov 2008 Location: New York, NY Posts: 385	Same problem here Mirror stuck after shutter release in AUTO modes and shutter speeds below Xsync. Originally, I had no idea what these symptoms indicated, but was fairly sure it wasn't stick mirror syndrome. What's more unfortunate is that I traded my baby k10d for this LX and don't have funds for a CLA. Tough luck!

09-29-2010, 11:37 AM	#27
AndrewG NY Veteran Member Join Date: Dec 2006 Location: Chappaqua, NY Photos: Gallery Posts: 688	I think you're already past this question but my LX will drop the mirror in auto, but I expect the exposure time to be somewhat inaccurate as the meter would have been calibrated for the reflectivity of film rather than that of the pressure plate. It is my understanding that Pentax may still be capable of servicing LX but I would expect it to be pricey...not sure about availability of specific parts but it would be worth asking as a working LX is pretty valuable. You can also look out for a donor LX, perhaps one with mechanical problems. I would also consider e-mailing Eric. Even if you don't end up sending it to him it is likely that based on what the other repair guy told you provide some good advice. I would expect that the camera still works well in manual mode?