Leica MR-4 suddenly malfunctions

[Greenhilltony]

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I purchased a Leica MR-4 last week and an adaptor to convert the voltage of an LR44 to the desired 1.35V of the Mercury PX625. They worked pretty well together at the beginning, the meter gave readings consistent with the M10-P and other meters I owned. Since last week, I sent my M4 to CLA so the MR-4 has not been touched for a while. Yesterday when I took it out again, it failed to work suddenly! The current status is summarized into the following points:

1. With the adaptor, after pushing the battery check slider, the needle stay perfectly on top of the silver dot.
2. Release the battery check slider, take a reading——the needle drops to the very bottom! Both for the black dot and red dot mode.
3. I found this last noon, and when I returned home at night, the MR-4 gave correct metering results again indoor. I thought it recovered. But when I woke up this morning and till now, it gets numb again, dropping to the bottom constantly.
4. When I cover the front window with my finger and push the reading slider, the needle does not go back to the zero position. Actually, the needle even does not respond to the coverage of the front window?!
5. It suddenly got normal once but then failed again.
6. When the battery is removed, pushing the reading slider let the needle sit to the zero position.

I wonder if it is repairable. I love the design that it could couple to the shutter speed dial of my M4 and M3. Although I’m totally capable of shooting without meter in a lot of situations, sometimes I want to reassure myself in complicated low-light, outdoor night street conditions. And aesthetically the MR-4 on top of the Ms is more attractive than the other external cold shoe meters.

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[Matlock]

2 hours ago, Greenhilltony said:

I purchased a Leica MR-4 last week and an adaptor to convert the voltage of an LR44 to the desired 1.35V of the Mercury PX625. They worked pretty well together at the beginning, the meter gave readings consistent with the M10-P and other meters I owned. Since last week, I sent my M4 to CLA so the MR-4 has not been touched for a while. Yesterday when I took it out again, it failed to work suddenly! The current status is summarized into the following points:

1. With the adaptor, after pushing the battery check slider, the needle stay perfectly on top of the silver dot.
2. Release the battery check slider, take a reading——the needle drops to the very bottom! Both for the black dot and red dot mode.
3. I found this last noon, and when I returned home at night, the MR-4 gave correct metering results again indoor. I thought it recovered. But when I woke up this morning and till now, it gets numb again, dropping to the bottom constantly.
4. When I cover the front window with my finger and push the reading slider, the needle does not go back to the zero position. Actually, the needle even does not respond to the coverage of the front window?!
5. It suddenly got normal once but then failed again.
6. When the battery is removed, pushing the reading slider let the needle sit to the zero position.

I wonder if it is repairable. I love the design that it could couple to the shutter speed dial of my M4 and M3. Although I’m totally capable of shooting without meter in a lot of situations, sometimes I want to reassure myself in complicated low-light, outdoor night street conditions. And aesthetically the MR-4 on top of the Ms is more attractive than the other external cold shoe meters.

The LR44 battery is an alkaline cell and is not really suitable for photo use, try an SR44 silver cell and that may resolve your problem.

[Greenhilltony]

45 minutes ago, Matlock said:

The LR44 battery is an alkaline cell and is not really suitable for photo use, try an SR44 silver cell and that may resolve your problem.

 

3 hours ago, Greenhilltony said:

an adaptor to convert the voltage of an LR44 to the desired 1.35V of the Mercury PX625.

 

I realized I made a mistake here! The adaptor came with a Zinc-air battery, not LR44 as I thought. It has 4 holes for air-inlet on the cathode side. Is that this kind of battery dies quickly? So that the meter could not be driven properly?

Edited August 31, 2023 by Greenhilltony

[nitroplait]

17 minutes ago, Greenhilltony said:

Are you suggesting the SR44 maintains the voltage output better than the LR44? I will look for one in the grocery stores.

Can't say if it solves the problem you experience, but you should never use alkaline (LR) in the voltage converters. The MR-9 from Kanto Camera states specifically that you must use silver-oxide (SR). If it is one of those converters -or similar, I think the correct battery is SR43 , but if a LR44 fits you should be OK with a SR44 (SR43 and 44 are both 1.55V).

SR44 can be difficult to find in regular grocery stores. Camera stores or electronics stores are more likely to stock them - I buy them online.

Not only does the silver oxide have a better depletion curve, it is also less likely to leak.

Edited August 31, 2023 by nitroplait

[Greenhilltony]

4 minutes ago, nitroplait said:

Can't say if it solves the problem you experience, but you should never use alkaline (LR) in the voltage converters. The MR-9 from Kanto Camera states specifically that you must use silver-oxide (SR). If it is one of those converters -or similar, I think the correct battery is SR43 , but if a LR44 fits you should be OK with a SR44 (SR43 and 44 are both 1.55V).

SR44 can be difficult to find in regular grocery stores. Camera stores or electronics stores are more likely to stock them - I buy them online.

Not only does the silver oxide have a better depletion curve, it is also less likely to leak.

I asked the dealer about the adaptor and found myself wrong in understanding the role of the adaptor. It just provides a container for the 1.4V zinc-air A675 battery, but do not convert the voltages. I can put an SR44 into it, but it comes back to the problem of using 1.55V for an un-modified MR-4.

[Greenhilltony]

The seller of the MR-4 sent it with a modern PX625 in it. It is 1.55V and thus the battery check puts the needle above the silver dot for 3 stops. If I cover the front window of the meter and take a reading, the needle goes to the zero position—better than the case I meet now with the adapted 1.4 V zinc-air battery. If the zinc-air battery drains so quickly, it means I have to prepare a batch of them in my bag?? Or ask someone knows it to modify the circuit to work under 1.5 V?

[Matlock]

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4 minutes ago, Greenhilltony said:

The seller of the MR-4 sent it with a modern PX625 in it. It is 1.55V and thus the battery check puts the needle above the silver dot for 3 stops. If I cover the front window of the meter and take a reading, the needle goes to the zero position—better than the case I meet now with the adapted 1.4 V zinc-air battery. If the zinc-air battery drains so quickly, it means I have to prepare a batch of them in my bag?? Or ask someone knows it to modify the circuit to work under 1.5 V?

A Wein Cell MRB625 zinc-air battery should last up to a year so no need to prepare more than one (it only takes 30minutes to come up to use).

[nitroplait]

1 hour ago, Greenhilltony said:

I asked the dealer about the adaptor and found myself wrong in understanding the role of the adaptor. It just provides a container for the 1.4V zinc-air A675 battery, but do not convert the voltages. I can put an SR44 into it, but it comes back to the problem of using 1.55V for an un-modified MR-4.

I use the dumb PX625 adaptors as well (see pic below). The Zinc-Air (1.4V) hearing aid batteries you buy cheaply at the drugstore or online are functionally as good as the very expensive Wein cells.

Regular Zinc-Air has a life of 4-8 months in my experience, Wein around a year - certainly not worth the premium. (all depending on usage, but normally the cell depletes from lack of use before the opposite)

The regular Zinc-Air cells I use (typically labeled 1.4V or 1.45V) actually measure 1.33-1.37V fairly constantly and works perfectly in my Leicameter MR, my Nikon FTn, my Nikon F photomics, my Pentax Spotmeter (which I no longer own), they also drop into my Ricoh 500G without adapter. I have also tested it with success on a friends Gossen Lunasix 3 and other devices that I fail to remember just now.

One thing to be mindfull about is that these types of batteries sweat a little and should not be left in the devices. In dumb brass adaptors the sweat causes a little corrosion on the inner brass surface with time and will need to be sanded on occasions to maintain contact.
For that reason I prefer the slightly cleaner but more expensive converter solution of the Kanto MR-9+SR43:

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Edited August 31, 2023 by nitroplait

[Greenhilltony]

19 minutes ago, nitroplait said:

I use the dumb PX625 adaptors as well (see pic below). The Zinc-Air (1.4V) hearing aid batteries you buy cheaply at the drugstore or online are functionally as good as the very expensive Wein cells.

Regular Zinc-Air has a life of 4-8 months in my experience, Wein around a year - certainly not worth the premium. (all depending on usage, but normally the cell depletes from lack of use before the opposite)

The regular Zinc-Air cells I use (typically labeled 1.4V or 1.45V) actually measure 1.33-1.37V fairly constantly and works perfectly in my Leicameter MR, my Nikon FTn, my Nikon F photomics, my Pentax Spotmeter (which I no longer own), they also drop into my Ricoh 500G without adapter. I have also tested it with success on a friends Gossen Lunasix 3 and other devices that I fail to remember just now.

One thing to be mindfull about is that these types of batteries sweat a little and should not be left in the devices. In dumb brass adaptors the sweat causes a little corrosion on the inner brass surface with time and will need to be sanded on occasions to maintain contact.
For that reason I prefer the slightly cleaner but more expensive converter solution of the Kanto MR-9+SR43:

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Simply register for free here – We are always happy to welcome new members!

 

Just ordered the MR-9 adapter. Hope my meter does not have other issues!

[Matlock]

33 minutes ago, Greenhilltony said:

Just ordered the MR-9 adapter. Hope my meter does not have other issues!

Keep us posted. One thing I would suggest is to use SR43 rather than SR44, they are slightly shallower so fit better and the very slightly smaller capacity will not be a problem on the MR-4 meter.

[Greenhilltony]

Strange, my MR-4 revived this morning, and stay in working until now. I have no idea what’s happening, I will keep an eye on it and update anything new.

[Huss]

13 hours ago, Greenhilltony said:

Strange, my MR-4 revived this morning, and stay in working until now. I have no idea what’s happening, I will keep an eye on it and update anything new.

You may want to clean the contacts in your meter, and clean your adapter.  Sounds like contact issues.

[Greenhilltony]

Have it checked and repaired by one of our Leica Masters in Hong Kong. He re-soldered every pins, wiped the optical units, tuned the circuit to work with 1.5 V batteries, and it works again!

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[Helge]

Am 7.9.2023 um 15:08 schrieb Greenhilltony:

Have it checked and repaired by one of our Leica Masters in Hong Kong. He re-soldered every pins, wiped the optical units, tuned the circuit to work with 1.5 V batteries, and it works again!

 

I‘m always wondering, how these „tunings“ or „adjustments“ actually work.

Either a lightmeter is dependent on an exact supply voltage, so any usage of batteries with an unstable output (like 1.5 V alkalines) wouldn’t work at all, since the voltage changes somewhat between 1.6 V and 1.2 V over lifetime.

Or the lightmeter works basically independent of it’s supply voltage, so any adjustment of the actual meter circuit is absolutely unnecessary, maybe limited just to the undervoltage test output only.

Which of the two is now correct for the MR-4?

Edited September 9, 2023 by Helge

[TomB_tx]

The MR4 meter circuit - like most of the CdS meters in cameras designed for constant-voltage Mercury cells - is not well balanced against changing supply voltage, and readings will change with a 1.5V cell. However, if shooting wide-latitude color negative film it may be close enough. The Pentax Spotmatic cameras had a better balanced meter circuit, and work well with either 1.3 or 1.5 V cells

[pixie]

Amazing it works! Mine was toast 2 years after purchase. I easily stripped it down, but never reliable.

I serviced 2 selenium meters for a friend and rec'd 2 in exchange! Been working till now! One on M3 and other on M2!

Personally move on..

[Helge]

vor 18 Stunden schrieb TomB_tx:

The MR4 meter circuit - like most of the CdS meters in cameras designed for constant-voltage Mercury cells - is not well balanced against changing supply voltage, and readings will change with a 1.5V cell. However, if shooting wide-latitude color negative film it may be close enough. The Pentax Spotmatic cameras had a better balanced meter circuit, and work well with either 1.3 or 1.5 V cells

You may be right, but why should I risk a wrong exposure with the wrong voltage, if there are working alternatives.

[Anbaric]

4 hours ago, Helge said:

You may be right, but why should I risk a wrong exposure with the wrong voltage, if there are working alternatives.

If you have your meter adjusted, you probably want to use a silver oxide cell that has an almost constant output until it dies (like the mercury cell did, but at a different voltage). Alkalines are problematic for their tendency to leak, too.

https://www.rokkorfiles.com/mercury.htm

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Hallo,

Look here: Leica M

[Helge]

Full acknowledge 

I usually get zinc-air batteries or sometimes silveroxide combined with a Schottky diode, since those solutions do not require any change to the meter‘s adjustment (some meters do even not allow such a big step, some have no oe bad documentation).