Spotmatic SP meter not working

Frosty66 · 04-13-2017, 01:20 PM

I have fixed the aparently common shutter/meter switch problem on this SP, so now for the meter problem itself. The batters compartment, wiring under the bottom place going to the meter switch and the switch contacts all seem intact but still the meter is not working.

The meter never moves and is always sitting the showing slightly negative.

What are the possibilities left ? I guess I need to pull the top cover off but if all the lower wiring and switch is intact as this one is, is it usually a bad sign that it's unrepairable without a donor body for parts ?

stevebrot · 04-13-2017, 03:44 PM - **1 Like**

Originally posted by Frosty66

What are the possibilities left ?

Bad capacitor? Corroded wire cores? Broken solder joint? Battery upside down? (positive pole should be on side facing the top of the camera) Bad meter cell?

Steve

Frosty66 · 04-13-2017, 04:11 PM

Yeah I guess I should get the meter out and make sure the wires are as solid as they look. Is the capacitor and cell something that is replaceable from any new standard parts or only from a donor body ?

stevebrot · 04-13-2017, 05:05 PM - **1 Like**

Originally posted by Frosty66

Yeah I guess I should get the meter out and make sure the wires are as solid as they look. Is the capacitor and cell something that is replaceable from any new standard parts or only from a donor body ?

Do you have the service manual?

Pentax Manuals

Note that there are both the Asahi manual and the National Camera manual for the Spotmatic on that page and both are useful (SP and SPII have identical meters).

Steve

officiousbystander · 04-13-2017, 05:42 PM - **1 Like**

I've had two old camera meters die within the space of a month. The quickest fix was an iPhone meter app which is quite good (MyLIghtMeter). I've also invested in a second hand Sekonic. Neither is as convenient as seeing a meter in the viewfinder but probably more consistent.

Frosty66 · 04-15-2017, 07:13 AM

Yes it may come to that for me too if I can't get it working. I have a couple of Weston Master III's which I have no idea how to use but I understand the values used on it are not the same as with latter day cameras?

I have the top off as well now and the wiring looks OK as well as the battery comparement and switch on the front so no obvious problems. I am going to get the multimeter out and just be sure I have no OK looking but dry solder joints. Just worried if I ever do find the cause I won't be able to get the parts anyway.

Nuno Almeida · 04-15-2017, 10:13 AM - **1 Like**

Indeed multimeter out, and go point by point starting at the sensor, no voltage there, back a bit, and so on till you find the culprit, good luck

Frosty66 · 04-15-2017, 02:52 PM

I found one wire broken off from it's soldering point on the PCB with the little potentiometer but still resting in place so it looked OK but wasn't, however resoldering that did not get it working by itself. I had previously repaired a proken wire that linked the two sensors, whilst trying to work out what was what from the circuit diagram I realised that this wire shoud also be linked to the -DC which apears to be the chassis (strange they use black for + and red for -), the wires were formed into a loop as if it would be screwed down somewhere but I can't see anywhere it would reach that looked like it had been previously used to hold down the wire to the chassis. The only one it really reached was one holding the viewfinder and CdS cells so I connected it there. Now the meter works !!!! I really thoughht that was a gonner ! Now how accurate the meter is I don't know but after it's back together I will try it out.

It is strange though as I can't see how the meter could ever have worked like that, I am wondering if I had two problems, the original wiring problem and another problem introduced by someone previously dismantling it ?

Topsy · 04-15-2017, 03:37 PM

I hope my meter problen will be fixed similarly, though mine seems quite a bit more complicated..

My meter rests in the right spot in the viewfinder when the battery is connected the proper way round, however only at 1/1000 and 1/500.. It's not in 'test' mode though and won't react to lighting changes.. For the top plate off too and didn't see anything yet. Haven't got a multimeter available at the moment. I finally need to buy one!

Frosty66 · 04-15-2017, 03:52 PM

Yeah that sounds a bit more involved, sounds like something iffy with the speed selector which according to the circuit diagram is a potentiometer. Good luck !

Xmas · 04-16-2017, 01:18 PM - **1 Like**

Originally posted by Frosty66

Yeah that sounds a bit more involved, sounds like something iffy with the speed selector which according to the circuit diagram is a potentiometer. Good luck !

Manuals

Frosty66 · 04-18-2017, 08:41 AM

All seems to be working, shutter and meter, had to open her up again after discovering the meter was intemittant and found another problem but so far so good. Apart from then I noticed the cocked indicator loose, not sure if I did something or if it was always like that but the long screw seems to be broken at the base so my options are drilling out the base and finding a new long screw, that that get smore involved as I'f probably have to retap the thread and then enlarge the upper shaft, second option is fitting some sort of sleeve over the top and bottom to hold it in place, third option is to just dispense with it which won't matter much but I think I will see if I can find something for option 2 first since it is fairly non invasive.

04-13-2017, 01:20 PM	#1
Frosty66 Senior Member Join Date: Dec 2016 Location: London, UK Posts: 181	Spotmatic SP meter not working I have fixed the aparently common shutter/meter switch problem on this SP, so now for the meter problem itself. The batters compartment, wiring under the bottom place going to the meter switch and the switch contacts all seem intact but still the meter is not working. The meter never moves and is always sitting the showing slightly negative. What are the possibilities left ? I guess I need to pull the top cover off but if all the lower wiring and switch is intact as this one is, is it usually a bad sign that it's unrepairable without a donor body for parts ?

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04-13-2017, 03:44 PM - 1 Like	#2
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Frosty66 What are the possibilities left ? Bad capacitor? Corroded wire cores? Broken solder joint? Battery upside down? (positive pole should be on side facing the top of the camera) Bad meter cell? Steve

04-13-2017, 04:11 PM	#3
Frosty66 Senior Member Join Date: Dec 2016 Location: London, UK Posts: 181 Original Poster	Yeah I guess I should get the meter out and make sure the wires are as solid as they look. Is the capacitor and cell something that is replaceable from any new standard parts or only from a donor body ?

04-13-2017, 05:05 PM - 1 Like	#4
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Frosty66 Yeah I guess I should get the meter out and make sure the wires are as solid as they look. Is the capacitor and cell something that is replaceable from any new standard parts or only from a donor body ? Do you have the service manual? Pentax Manuals Note that there are both the Asahi manual and the National Camera manual for the Spotmatic on that page and both are useful (SP and SPII have identical meters). Steve

04-13-2017, 05:42 PM - 1 Like	#5
officiousbystander Pentaxian Join Date: Mar 2014 Location: Sydney Photos: Gallery Posts: 912	I've had two old camera meters die within the space of a month. The quickest fix was an iPhone meter app which is quite good (MyLIghtMeter). I've also invested in a second hand Sekonic. Neither is as convenient as seeing a meter in the viewfinder but probably more consistent.

04-15-2017, 07:13 AM	#6
Frosty66 Senior Member Join Date: Dec 2016 Location: London, UK Posts: 181 Original Poster	Yes it may come to that for me too if I can't get it working. I have a couple of Weston Master III's which I have no idea how to use but I understand the values used on it are not the same as with latter day cameras? I have the top off as well now and the wiring looks OK as well as the battery comparement and switch on the front so no obvious problems. I am going to get the multimeter out and just be sure I have no OK looking but dry solder joints. Just worried if I ever do find the cause I won't be able to get the parts anyway.

04-15-2017, 10:13 AM - 1 Like	#7
Nuno Almeida Senior Member Join Date: Sep 2014 Location: Aveiro Posts: 179	Indeed multimeter out, and go point by point starting at the sensor, no voltage there, back a bit, and so on till you find the culprit, good luck

04-15-2017, 02:52 PM	#8
Frosty66 Senior Member Join Date: Dec 2016 Location: London, UK Posts: 181 Original Poster	I found one wire broken off from it's soldering point on the PCB with the little potentiometer but still resting in place so it looked OK but wasn't, however resoldering that did not get it working by itself. I had previously repaired a proken wire that linked the two sensors, whilst trying to work out what was what from the circuit diagram I realised that this wire shoud also be linked to the -DC which apears to be the chassis (strange they use black for + and red for -), the wires were formed into a loop as if it would be screwed down somewhere but I can't see anywhere it would reach that looked like it had been previously used to hold down the wire to the chassis. The only one it really reached was one holding the viewfinder and CdS cells so I connected it there. Now the meter works !!!! I really thoughht that was a gonner ! Now how accurate the meter is I don't know but after it's back together I will try it out. It is strange though as I can't see how the meter could ever have worked like that, I am wondering if I had two problems, the original wiring problem and another problem introduced by someone previously dismantling it ?

04-15-2017, 03:37 PM	#9
Topsy Veteran Member Join Date: Feb 2014 Photos: Gallery \| Albums Posts: 625	I hope my meter problen will be fixed similarly, though mine seems quite a bit more complicated.. My meter rests in the right spot in the viewfinder when the battery is connected the proper way round, however only at 1/1000 and 1/500.. It's not in 'test' mode though and won't react to lighting changes.. For the top plate off too and didn't see anything yet. Haven't got a multimeter available at the moment. I finally need to buy one!

04-15-2017, 03:52 PM	#10
Frosty66 Senior Member Join Date: Dec 2016 Location: London, UK Posts: 181 Original Poster	Yeah that sounds a bit more involved, sounds like something iffy with the speed selector which according to the circuit diagram is a potentiometer. Good luck !

04-16-2017, 01:18 PM - 1 Like	#11
Xmas Veteran Member Join Date: Mar 2015 Posts: 617	Originally posted by Frosty66 Yeah that sounds a bit more involved, sounds like something iffy with the speed selector which according to the circuit diagram is a potentiometer. Good luck ! Manuals

04-18-2017, 08:41 AM	#12
Frosty66 Senior Member Join Date: Dec 2016 Location: London, UK Posts: 181 Original Poster	All seems to be working, shutter and meter, had to open her up again after discovering the meter was intemittant and found another problem but so far so good. Apart from then I noticed the cocked indicator loose, not sure if I did something or if it was always like that but the long screw seems to be broken at the base so my options are drilling out the base and finding a new long screw, that that get smore involved as I'f probably have to retap the thread and then enlarge the upper shaft, second option is fitting some sort of sleeve over the top and bottom to hold it in place, third option is to just dispense with it which won't matter much but I think I will see if I can find something for option 2 first since it is fairly non invasive.