I have the mirror box lever problem in a spotmatic
Ok, the problem may well be the mirror charge latch. This is very commonly the cause of failure to wind or fire. The catch will be out of sync with the charging lever etc and so the mirror springs will not stay tensioned.
If it is, the cammera will be stuck with the shutter charged (Cocked) but will not fire because the mirror has not been properly primed. (The shutter is actually fired by the mirror. The shutter button actually releases the mirror.)
The locking arm keeps the main mirror spring tensioned until the closing shutter blind has fully closed. The blind roller engages with a gear which releases the
Remove the bottom cover. There is a long lever shiny arm engaging a crank-pin on winder gear extending to a point just below camera-right of the lens mount. It pivots on a large screw, and there is a largish wire spring which extends to engage a small hole in the end of a lever near the arm end, that dissapears into the camera.
The lever with the hole in it is the mirror charging arm, the long shiny lever pushes this towards the front of the camera to tension the mirror springs, when the film advance is operated.
Next to this is a shorter arm which extends over a gear at one end and is free at the other. This is the latch. The gear wheel engages a small pinion which is in fact the end of the blind roller for the closing curtain/blind. A peg on this gear strikes the other end of the latch to move it out the way and release the mirror tension after the shutter has finished, and this in trun resets the mirror, and releases the winder.
When the mirror is charged the mirror charging arm is held in the tensioned position by the 'free' end of the latch. If the shutter is ready to fire the charging arm should be pressing against the free end. If it isn't the camera will not fire.
To fix this it is easier if the shutter is fired. To do this first remove the large screw holding the long arm. Not forgetting the spring! There is a washer which must be removed too. Do not lose this it is important. This gets it out of the way. now push the charging arm towards camera front as far as it will go. You won't get it all the way, as the latch will be in the way, just as far as you can. If it isn't in the way, then this is not your problem!
Holding it in this position, press the shutter release. This should fire the shutter. If it does not fire then you may also have to remove the latch to allow you to push the arm forwards a little more. (In fact if you can hold the arm in the primed position you could replace the catch in the primed position. This is awkward though!)
When the shutter has fired the latch should move to the 'reset' position, allowing the charging arm to be pushed past it's end. If this is OK, you need to push the lever back to the reset postion. The mirror will remain in the up postion until you do this.
Now you can replace the long arm, again not forgetting the spring. The screw that holds that on has a shoulder, that the spring loops around, and the washer has a flat spot in the hole which means it has to be fitted in the right position. The end of the spring should poke through the mirror arm hole. The easiest way to reassemble this is to put the arm in, then fit the washer. Now place the spring loosely in position, and then put the screw in place loosley. This allows you to manuver the end of the sprion into the hole, You can then carefully tighten the screww. The washer has a tendency to become dislodged so you might have to try this a couple of times. (A blob of grease here can help keep the washer in place.)
If that's all OK then you should be able to wind and fire. If everything seems fine, check the screws are firm (Don't overtighten any!) and replace the bottom cover.
This is a very common fault, and is often caused by jarring the camera just at the wrong monent, but it can develop in an old camera (and they all are!) just due to wear. The latch has in fact changed in shape several times in the lifteime of this mechanism (and it was still in use in K1000's in 1997!) and is the mst common single cause of jams in these cameras.
A little lubrication can help. A spot of lighter fluid can be used to remove old oil and grease from the winder gear, the cocking arm pivot, anf the latch pivot. A tiny amount of grease can be applied to the slow moving pivots and contact points only. A tiny drop of watch oil can be used on the latch pivot. and the opeating peg, but no oil must get into the axle or teeth of the gear itself. This can cause uneven and erratic running of the curtain.