Cosina CSL fast shutter speeds problem

[Stuart Walker]

I have a Cosina CSL, (similar to CSM, and maybe others) which has a horizontal cloth shutter controlled by an electromagnet. With a bit of bending and and adjusting of the magnet and the operating arm, (accessed from the bottom of the camera) I can get all the slow speeds up to 1/60 to work alright, but the speeds above that either don't work at all, that is the blinds travel across together with no gap, or all the higher speeds seem to be about 1/60, checked by viewing the computer monitor through the shutter a la Rick Oleson. Other cameras I have give results similar to those on Rick's site, so there is a problem with this particular camera. I've had the top cover off but I can't see anything obvious. Is the problem in the electronics, or elsewhere, any ideas? (It's quite a neat little M42 camera, which it would be nice to get working properly, or would it be quicker to just
buy another one?)

[John Parry]

Hi Walkersj - What's your name? Put it in your profile - we can't go on calling you that.

What that camera needs is a little bit of lead in the bottom right hand corner. Best way to get it in there is a Colt 45!

Reards - John

[Stuart Walker]

Shooting it sounds a bit drastic! Anyway I was wondering if we have any electronics experts, to help with these later cameras? I can manage the mechanical ones, but it's difficult to figure out electronics without circuit diagrams. I did e-mail Cosina on the hope they might dig out a bit of technical info. They did have the courtesy to reply but not much help;

Dear Mr. Walker,

Thank you for using our camera.
Sorry but we can not supply spare parts directly consumers.
Please contact where you bought the camera, and ask them to check and repair it.


Best regards.,
Goda

I can see some external capacitors which I hope might be where the problem is, otherwise if it's the main IC then there's probably not much hope. However the meter and slow speeds all work OK, so it's tantalisingly almost working!

Regards

Stuart

[Stuart Walker]

With a bit more fiddling around with adjusting the position of the electromagnet I can sort of get 1/125 and 1/250 speeds working. If you have the electromagnet pushed up hard against the release arm then all the fast speeds seem to be 1/60, if you have it barely touching the blinds don't open. Somewhere in between you can sort of get a few faster speeds, albeit they don't seem very consistent. It seems to be rather sensitive, the mechanical timers seem more consistent. Anyone know if this means their is some critical adjustment of the release arm and the electromagnet, or is there some electrical/electronic adjustment, or am I wasting my time? I don't really like to give up on something, especially when it's almost working.

[Stuart Walker]

Well I've come back to this camera and after reading about Fujica
cameras being fixed by changing the capacitors I thought I would give
it a go. It didn't make any difference! So I tried some new batteries and lo and behold one of the batteries was faulty and only produced about 0.2V but the shutter now almost works on the faster speeds. The battery voltage is so low the light meter doesn't even work, so what does this mean? Is there some sort of voltage regulator thats supposed to drop the voltage to the electromagnets?

[kiev4a]

I could tell you what to do to keep a Leica II shutter from capping but I would have to go along with Sir John on this one--.45 cal. ball ammo! We tend to be on the mechanical side here.

[John Parry]

Hey Stuart - welcome to the board.

I've a couple of Fujicas that have shown the same symptoms as yours - works a treat as you put the new batteries in, but you watch the lightmeter falling even as keep the light levels even.

How much time are you prepared to spend? You could probasly get a poor copy of a service manual off eBay for £15, you will need special tools, and serious faultfinding abilities.

Wayne's solution may be the best!

Regards - John.

[PeterW]

Stuart,

I know very little about electronic camera shutter control so this is very far removed from being 'expert' advice, but back when I was into hi-fi I played with transistorised and chipped audio amps for a time. Is it possible that the 'voltage regulator' is a bad contact or a 'dry' soldered join somewhere in the circuit?

I once 'cured' a non-working meter on a camera by cleaning the inside of the screw-down battery cap and checking the contact between the bottom plate where the cap screwed in and the body of the camera. Someone had used some felt light trapping inside the bottom plate because it was slightly distorted, and also made sure the screws didn't come loose by coating the threads in Loktite - both quite efficient insulators.

I've never even looked inside a Cosina CSL, but from what you say about everything else working, and fiddling with the electro magnet giving 'half a solution', it's possible that the electro-magnet, or the voltage to it, is the source of the problem. I've read that on some electronic shutter control systems these sometimes develop unreliable action because of bad contacts, or sometimes because of low voltage to them, and give faults that can be difficult to pin-point. Trouble is, you need to know what the voltage at the magnet should be before you know whether the problem is mechanical or electrical.

Alternatively, are there any pre-set variable trimming resistors anywhere in the circuit to it? In amps I found these often developed bad contact and were quite a prolific source of distortion, crackling and other ill effects.

It's always better to try to isolate a fault by testing rather than replace bits and pieces in hope. If you can find a factory repair manual they often give recommended voltage readings at various circuit points - sometimes relative to 'chassis earth' but just occasionally relative to another point on the circuit to check for voltage drops.

That's how I found what was the matter with shutter speed problems on my spare Canon T70 body. One of the speed selector button switches has a high internal resistance. Canon's UK service department were very helpful, and more or less 'talked me through' the check procedure. Curing it's another matter because the switch is sealed as one of a pair. Easy enough to fit a replacement pair, but Canon no longer stock any; not, it seems, even in Japan. It's a simple 'press to make, release to break' switch so if I can find yet another round tuit I'm toying with the idea of fitting a similar small switch from something like an auto remote central locking/alarm control. Nothing to lose, because the body's useless at the moment.

As Cosina can't - or won't - help, you could try asking on the various camera repair forums. There's a lot of ex-pro techies out there, and maybe someone's got a manual and could copy the relevant bits for you.

Hope you get some joy. You never know, you might even get to enjoy electronic trouble shooting (some people do) and become your own 'expert'! Personally I've never really cared much for trying to trace faults in electronic circuits, I prefer mechanical bits that I can see working without having to try to 'see' via a meter.

Not a definitive answer I'm afraid, and maybe even way off-beam, but maybe possibly a pointer or two.

Good luck!

PeterW

[Stuart Walker]

Thanks for replies. I must admit that I prefer the mechanical ones, and this Cosina probably isn't worth the trouble, but it's become a sort of challenge! It's tantalisingly close to working, but so much for electronics being more reliable than mechanisms. Anyway the strange thing is that the shutter works better with a low voltage. I had bought five new batteries, two for this camera and three for a Fujica thinking this would give a bit extra oomph but it was actually worse! However one of the five batteries was faulty only showing about 0.2V instead of 1.55V on the multimeter which the Fujica didn't like at all, but strangely the shutter on the Cosina seemed to work betterusing one good battery and one bad one, albeit not perfectly, and the voltage was so low that the light meter LEDs didn't even work. Strange. If anyone has access to a service manual and could let me have a copy then I would be grateful and I could check out the voltages. Of course it could be some irrepaceable component that has gone down. You can't make electronic bits with a hacksaw file.