Yashica Electro GTN -- Intermittent Shutter

[ColSebastianMoran]

Yashica Electro GTN, the shutter is intermittent. That is, sometimes it gives the correct shutter timing, sometimes it reverts to 1/500th.

Like the icon of head hitting brick wall, it will work a couple of times, then start reverting to 1/500th. Russ Sisco has just had a look at this and done a nice cleanup of the camera, but we don't know what to do next.

Whether it's it's good (right shutter timing) or bad (1/500th only), the battery check lights up, and the yellow "Turn to wider aperture" light goes on. So, it's not just an interruption of battery power.

Can anyone suggest what component would be failing to produce this result? I have a parts camera ready.

 

[farlymac]

I would think it has to be in the electronic part of the camera, if everything else that's mechanical checks out. Components will sometimes become intermittant before they fail completely.

PF

 

[SallyShears]

Yes, sounds like it's electronic.

 

[dogbunny]

I got this from the Yashica Guy's website:

"Erratic Exposure Test: A primary cause of erratic exposure occurs when the lube in the shutter dries and gums up the works. One simple test for this is to attach a strobe flash to the camera, and fire several shots to see if the flash goes off each time. You do not need film in the camera to wind the shutter. Set the shutter at AUTO and proceed. In the "G" series of cameras, the flash will not fire until the shutter blades reach their extreme outer travel limit. A shutter with bad lube will only sometimes if ever fire the flash, so you have now pinpointed the most likely cause of the problem."

Have you given this a try? I have a similar problem with my GTN. Battery and all the lights seem to work fine, but sometimes in reverts to the no battery shutter speed. I was going to play around with mine tonight. Such a shame because the camera is in new condition cosmetically.

 

[dogbunny]

One more thing I noticed. . . With my particular GTN , when I put it in Bulb setting it doesn't stay open when I depress the shutter. Odd, cuz the meter seems to work just fine and everything on it is clean as a whistle. Oh well.

 

[ColSebastianMoran]

Dogbunny, glad to hear that I'm not alone.

On my intermittent GTN... In it's bad mode, the camera will trigger a flash, every time, no problem. I expect it will do so in good mode as well.

In it's bad mode, on B, all the lights work fine, but the shutter does not stay open. That's consistent, I think. In this camera, the electric circuitry keeps the shutter open. Since the lights work, a lot of the connections and circuitry must be OK, but in bad mode the solenoid (electromagnet) is not holding the shutter open.

Circuit diagram is on pg 59-64 of the Yashica Electro Repair Manual. And, that manual is at:

http://www.scribd.com/doc/16600004/Yashica-Electro-Repair-Manual

 

[ColSebastianMoran]

Looking for help to figure out this circuit diagram... What failure would result in the behaviors I see out of my GTN camera?

The behaviors are:
- All three lights work as expected (Batt test, over, under. The lights react properly to changes in f/stop and lighting. Under light comes on at about the right light level)
- On Auto, shutter runs at 1/500th, doesn't stay open for as long as it should
- On Bulb, shutter runs at 1/500th, doesn't stay open as it should
- On Flash, shutter also runs (I think) at 1/500th.

Camera has just had a good CLA. The POD is good.

Here's the circuit diagram:

And, here's a link to a full-page PDF of this diagram, with a good text explanation of the exposure cycle.

http://2under.net/private/Yashica-Electro-Repair-Manual-pg64.pdf

Finally, here is the text explanation of the exposure cycle:

When the shutter-release switch reaches the bottom of its stroke, it connects the timing capacitor C1 to the circuit. Also, the shutter releases and the blades move to the open position.
Transistor TR1 remains turned off while the timing capacitor charges to the required voltage. Consequently, transistor TR4 conducts current through the electromagnet. The electromagnet holds its armature to keep the blades in the open position. The time it takes for the timing capacitor to charge depends on the resistance of the CdS cell. When the timing capacitor reaches a sufficient charge, the voltage on its positive plate turns on translator TR1 -- This trigger voltage depends on the diaphragm setting which determines the resistance in the emitter circuit of TR1. TR1 turns on TR2, and TR2 turns on TR3. Now, TR3 robe transistor TR4 of the base current it needs to conduct. TR4 shuts off, depriving the electromagnet of current.
As the blades close, the blade-operating ring closes the capacitor-shoring switch S3. S3 opens as the blades open and closes as the blades close. So the time that S3 opens determines when the timing capacitor can start accepting a charge. The eccentric adjustment an S3 is your high-speed adjustment point.

 

[ColSebastianMoran]

Here's what I've figured out from reading the diagram:

1. If the Capacitor Shorting Switch S3 never closes, then the capacitor is always charged and the circuit never holds the blades open. Everything would look fine in the "red" and "yellow" positions of the shutter release switch. Check voltage across the cap.

2. If the electromagnet is dead or the circuit to it is open, then it never holds the blades open. Check continuity from T4 thru Electromagnet and on to the + side of battery.

3. If TR4 is working well enough to light the yellow ("under") lamp, but not to provide the current for the electromagnet. How to check?

Those are the only failures I can see which would have all the lights working properly and still not have the electromagnet hold the shutter open. I think that proper working of the lights means that all four transistors are working properly. Right?

Any other insights to this circuit or into what usually fails to cause this behavior?

 

[ColSebastianMoran]

Bumping this thread.

Anyone out there who can read this circuit diagram? What failures would produce the results observed: the shutter goes to the default 1/500th while all three lights continue to function as expected.

 

[tomisimpern]

hi there,
I'm sure I read that the metering and shutter-release are 2 different circuits. Since 1/500 is the default speed used when battery fails on the GTN, could this not be a break in the shutter circuit. Metering circuit is intact obviously.
Sorry if that sounds a bit simplistic, but I'm not electrically-minded to work out if it could be a capacitor or other IC part.
Tony

 

[jrbrubaker]

I'm having the exact same problem with my GSN. Everything appears to be working, lights come on when expected, etc. But for no apparent reason it will default to what sounds like 1/500th unexpectedly for a couple frames, then work again. It's most frustrating, especially since I can't get it to consistently recreate the problem.

I wonder a bit about the cold effecting things, since this seems to have happened a bit more in chilly weather, but that might just be my imagination.

Anyone else?

 

[ColSebastianMoran]

Mine was intermittent as well. Would run OK for a bit, then fall back to the default of 1/500th. Someone on another site suggested that this could happen if the slide switches are not making good contacts, but on mine Russ has done the POD and cleaned up the slide switches. If you haven't had the camera apart for POD and adjusting the slide switches, that might help. Meanwhile, I would love to find enough circuit savvy to know what failures in the circuit diagram would lead to this behavior.

 

[ColSebastianMoran]

hi there,
I'm sure I read that the metering and shutter-release are 2 different circuits. Since 1/500 is the default speed used when battery fails on the GTN, could this not be a break in the shutter circuit. Metering circuit is intact obviously.

Tony, thanks for the comment, and sorry I didn't acknowledge it earlier.

Yes, for example, a break in the wire to the electromagnet would leave everything else working and the shutter falls back to 1/500th (it's mechanical speed if not held open by the magnet). Russ has had my camera apart, so I doubt it's a broken wire in my case.

 

[b1bmsgt]

On Richards camera, I checked all the wires and solder connections and didn't find anything questionable, unfortunately.

Russ

 

[monopix]

Here's what I've figured out from reading the diagram:

<snip>

Those are the only failures I can see which would have all the lights working properly and still not have the electromagnet hold the shutter open. I think that proper working of the lights means that all four transistors are working properly. Right?

Any other insights to this circuit or into what usually fails to cause this behavior?

You basically understand what's happening.

The one thing to be aware of is that the switch position is different when the check lights are illuminated than when the shutter is fired so, if one switch position is open circuit this can cause the meter to work but not the shutter control. I would definitely suspect switches as a starting point.

 

[ColSebastianMoran]

Thanks, monopix.

 

[farlymac]

Could be that the circuit board is out of alignment just enough to break the shutter circuit every once in a while, instead of all the time. There is an adjustment screw on the bottom to take care of that, and I think it is mentioned in another post in this part of the forum. Or maybe on another forum, but if not here, I'll post the info for all when I come across it again.

PF

 

[farlymac]

Hi merehzezi,
If it's 2mm thick then it may be that you need to adjust the shutter rod (as I call it) which can control when the shutter is tripped. I had similar on my Electro 35CC and it took a bit of micro-adjustment to get it tripping in the correct (to me) place.

This is what I found here. I think the instructions were on another forum, so I'll look there for the info.

PF

 

[farlymac]

I found it. In the Repair Forum.

Update: I just did a POD on a 2nd electro, had the same problem (lag/miss). I think this is probably related to the new pad being slightly too thick. There's a related thread on flickr about this. Here's how I solved it, on one of the electros (haven't tested other one yet):

1. Remove bottom cover
2. On the left side, there are 2 brass adjustment screws, one larger and one smaller. The smaller one is to the left of the larger one and further in. Turn this counterclockwise. I believe this adjusts the shutter button stroke somehow and compensates for a slightly thicker pad.

**Update** This has solved the above problem on both cameras. Note, if you turn the rod too far in the opposite direction, it can also cause problems.

Try that, and see if it clears things up.

PF

 

[ColSebastianMoran]

Farlymac, thanks, I've got the idea.

By the way, reading over this whole thread, I'm worried that I may have left an incomplete impression of the work Russ did on this camera. Russ was terrific. When I sent it, he immediately got back to me that there was an electrical problem that he probably could not solve. I had the opportunity to drop the whole thing right there with no charge. I told him to go ahead with his complete work-up of the camera, including POD, clean-up, lights, and adjustments. He did exactly what I asked of him.

It's me that has the pig-headed determination that this can be fixed. Or maybe I just enjoy the chase. If I find an answer, I'll post it. I think there are quite a few Electros with shutters that fall-back to the default 1/500th.

I suppose I could just load up Tri-X and shoot everything at 1/500th using Sunny-16.

Thanks, all for the help. I think I'll let this lie till I have time to dig in further.