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landstrykere · 03-18-2018, 10:49 AM

I have got a Spotmatic for parts because the advance lever was stuck. I have fixed that, also have cleansed and lubricated a bit the mechanism, cleansed focus screen, mirror, viewfinder. So i have an extra functional Spotmatic

.
I try now to fix the base plate. The inside of the battery cover was covered in green corrosion. Was this from old mercury oxide batteries? I have just scratched away most of the corrosion with a blade but the covr is stuck. Some former owner tried hard to unscrew it. By the color it looks like coated (or plated?) brass and the whole base plate may be the same metal.
Some chemical would be needed to unlock this. Just don't know what to use: an acidic or a basic one?

(pictures taken with the Super Takumar 1:4/100mm at f16 in M mode, iso 200 with a K-5)

**darylk** · 03-18-2018, 11:02 AM

I would try WD40 before anything else. It's specifically made for this type of problem.

Xmas · 03-18-2018, 11:11 AM

Or vinegar drip on end of darning needle.

Not a Number · 03-18-2018, 11:20 AM

According to Wikipedia the electrolyte used in mercury cells is Sodium or Potassium hydroxide which are basic/alkaline.

maw · 03-18-2018, 04:50 PM

Originally posted by landstrykere

I try now to fix the base plate. The inside of the battery cover was covered in green corrosion.

I solved often with an acid base, you can try
which is a suitable product that melts the rods, otherwise also the hydrogen peroxide, or even Lemon or Vinegar pour it several times around the thread until it penetrates deeply,
then use a larger screwdriver, try to repeat the operation several times in the case.

**pentaxus** · 03-18-2018, 05:37 PM

I would use a penetrating oil like Liquid Wrench. Using an acid like Lime Away can also work. Also use a lot of patience. It may take a week or so.

Not a Number · 03-18-2018, 06:57 PM

Penetrating oils usually have a acid component. That's what makes them penetrating.

ctrout · 03-19-2018, 05:34 AM

I would get a new base plate. Want one? I have an extra, I think.

landstrykere · 03-19-2018, 11:03 AM

thanks all!

yesterday it was soaked in WD40-like. Now I have rinsed and try to unscrew but it's damn stuck. So after a good cleaning to wash away wd40 remains, it's now soaking in strong vinegar. I'll see tomorrow...

---------- Post added 03-19-18 at 11:09 AM ----------

Originally posted by pentaxus

Also use a lot of patience. It may take a week or so.

I seems so... I was looking on Ebay, and few Spotmatic are sold with the same issue: stuck battery cover... I think it's due to the use of alkaline batteries, that leak and the corrosive compound glues the thread.

---------- Post added 03-19-18 at 11:11 AM ----------

Originally posted by ctrout

I would get a new base plate. Want one? I have an extra, I think.

thank you! much appreciated. Just for curiosity, to know the do-ability of this, I'll wait some days

titrisol · 03-20-2018, 04:55 AM

Vinegar is the way to go, you do not need much acidity or it will corrode the aluminum
do not soak all plate, but drip slowly into the threads

landstrykere · 03-20-2018, 07:58 AM

Originally posted by titrisol

Vinegar is the way to go, you do not need much acidity or it will corrode the aluminum
do not soak all plate, but drip slowly into the threads

you are right. After one day in 7% white vinegar, with some force but not too much applied with a big flat screwdriver end in the damaged cap slot, and it has loosened up. Yes I was wondering how much acidity could also affect the rest of the plate, as at first I wanted to use a 35% vinegar then finally opted for this lower, regular dilution. The plate seems to not be affected (what is seen on it was already there, maybe caused by some former tape glue and/or tinkerings around the battery cap). I let it soak a bit more in order to dissolve corrosion still in the thread. Then brushing of the thread and thorough wash.

Next step is to rebuild the battery cap with some metal epoxy putty and dremeling of a slot, then try the meter (silver-oxyde SR45/V394 battery from the nearest Clas Ohlson).

**TomB_tx** · 03-20-2018, 09:58 AM

As an alternative to trying to repair the cover, there is a battery adapter that replaces the cover:
H-B Adapter. Replacement for PX400, EPX400 or RM400 discontinued Mercury cells.

landstrykere · 03-20-2018, 10:13 PM

Originally posted by TomB_tx

As an alternative to trying to repair the cover, there is a battery adapter that replaces the cover:
H-B Adapter. Replacement for PX400, EPX400 or RM400 discontinued Mercury cells.

thanks. Interesting site. I may buy one of these adapters.
In the meanwhile I did repair the cap with a bit of metal epoxy. Not pretty but fully functional.

03-18-2018, 10:49 AM	#1
landstrykere New Member Join Date: Nov 2017 Location: Nittedal Posts: 24	Spotmatic: acidic or basic chemical cleaning of base plate ? I have got a Spotmatic for parts because the advance lever was stuck. I have fixed that, also have cleansed and lubricated a bit the mechanism, cleansed focus screen, mirror, viewfinder. So i have an extra functional Spotmatic . I try now to fix the base plate. The inside of the battery cover was covered in green corrosion. Was this from old mercury oxide batteries? I have just scratched away most of the corrosion with a blade but the covr is stuck. Some former owner tried hard to unscrew it. By the color it looks like coated (or plated?) brass and the whole base plate may be the same metal. Some chemical would be needed to unlock this. Just don't know what to use: an acidic or a basic one? (pictures taken with the Super Takumar 1:4/100mm at f16 in M mode, iso 200 with a K-5)

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03-18-2018, 11:02 AM	#2
darylk Site Supporter Join Date: Sep 2010 Location: Blue Hill, Nebraska Photos: Gallery Posts: 494	I would try WD40 before anything else. It's specifically made for this type of problem.

03-18-2018, 11:11 AM	#3
Xmas Veteran Member Join Date: Mar 2015 Posts: 617	Or vinegar drip on end of darning needle.

03-18-2018, 11:20 AM	#4
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	According to Wikipedia the electrolyte used in mercury cells is Sodium or Potassium hydroxide which are basic/alkaline.

03-18-2018, 04:50 PM	#5
maw Pentaxian Join Date: Feb 2014 Location: Sassari (Italy) Posts: 1,118	Originally posted by landstrykere I try now to fix the base plate. The inside of the battery cover was covered in green corrosion. I solved often with an acid base, you can try which is a suitable product that melts the rods, otherwise also the hydrogen peroxide, or even Lemon or Vinegar pour it several times around the thread until it penetrates deeply, then use a larger screwdriver, try to repeat the operation several times in the case.

03-18-2018, 05:37 PM	#6
pentaxus Site Supporter Join Date: Jun 2010 Location: Central Coast, CA Posts: 1,320	I would use a penetrating oil like Liquid Wrench. Using an acid like Lime Away can also work. Also use a lot of patience. It may take a week or so.

03-18-2018, 06:57 PM	#7
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	Penetrating oils usually have a acid component. That's what makes them penetrating.

03-19-2018, 05:34 AM	#8
ctrout Veteran Member Join Date: Aug 2016 Photos: Gallery Posts: 444	I would get a new base plate. Want one? I have an extra, I think.

03-19-2018, 11:03 AM	#9
landstrykere New Member Join Date: Nov 2017 Location: Nittedal Posts: 24 Original Poster	thanks all! yesterday it was soaked in WD40-like. Now I have rinsed and try to unscrew but it's damn stuck. So after a good cleaning to wash away wd40 remains, it's now soaking in strong vinegar. I'll see tomorrow... ---------- Post added 03-19-18 at 11:09 AM ---------- Originally posted by pentaxus Also use a lot of patience. It may take a week or so. I seems so... I was looking on Ebay, and few Spotmatic are sold with the same issue: stuck battery cover... I think it's due to the use of alkaline batteries, that leak and the corrosive compound glues the thread. ---------- Post added 03-19-18 at 11:11 AM ---------- Originally posted by ctrout I would get a new base plate. Want one? I have an extra, I think. thank you! much appreciated. Just for curiosity, to know the do-ability of this, I'll wait some days

03-20-2018, 04:55 AM	#10
titrisol Pentaxian Join Date: Dec 2007 Location: In the most populated state... state of denial Photos: Gallery \| Albums Posts: 1,854	Vinegar is the way to go, you do not need much acidity or it will corrode the aluminum do not soak all plate, but drip slowly into the threads

03-20-2018, 07:58 AM	#11
landstrykere New Member Join Date: Nov 2017 Location: Nittedal Posts: 24 Original Poster	Originally posted by titrisol Vinegar is the way to go, you do not need much acidity or it will corrode the aluminum do not soak all plate, but drip slowly into the threads you are right. After one day in 7% white vinegar, with some force but not too much applied with a big flat screwdriver end in the damaged cap slot, and it has loosened up. Yes I was wondering how much acidity could also affect the rest of the plate, as at first I wanted to use a 35% vinegar then finally opted for this lower, regular dilution. The plate seems to not be affected (what is seen on it was already there, maybe caused by some former tape glue and/or tinkerings around the battery cap). I let it soak a bit more in order to dissolve corrosion still in the thread. Then brushing of the thread and thorough wash. Next step is to rebuild the battery cap with some metal epoxy putty and dremeling of a slot, then try the meter (silver-oxyde SR45/V394 battery from the nearest Clas Ohlson).

03-20-2018, 09:58 AM	#12
TomB_tx Loyal Site Supporter Join Date: Jun 2011 Location: Texas Photos: Gallery Posts: 1,446	As an alternative to trying to repair the cover, there is a battery adapter that replaces the cover: H-B Adapter. Replacement for PX400, EPX400 or RM400 discontinued Mercury cells.

03-20-2018, 10:13 PM	#13
landstrykere New Member Join Date: Nov 2017 Location: Nittedal Posts: 24 Original Poster	Originally posted by TomB_tx As an alternative to trying to repair the cover, there is a battery adapter that replaces the cover: H-B Adapter. Replacement for PX400, EPX400 or RM400 discontinued Mercury cells. thanks. Interesting site. I may buy one of these adapters. In the meanwhile I did repair the cap with a bit of metal epoxy. Not pretty but fully functional.

Spotmatic: acidic or basic chemical cleaning of base plate ?

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