Pentax MG shutter fix
Wherein I try to get a parts-only MG to work again.
Why put all this effort into the humble MG? Because I would rather my first attempt be on an MG then a ME Super, which is next on the fix list...
As you can see in the above picture the uppermost shutter blade was out of place, and evidently the shutter didn't work.
I was never able to find a service manual for the MG so used the ME and ME Super manuals from Mark Robert's site (http://www.robertstech.com/pentax.htm). The ME manual is closer to the MG, but the ME Super manual has a very handy parts list and the exploded drawings are much clearer.
I actually ended up taking 2 MGs apart and am still in the process of putting one back together again (we will see if I am forced to rename it "Humpty-Dumpty MG".) While taking apart the second MG I realized I didn't have to disassemble everything that the manual tells you to, or sometimes I did it in a different order. For instance it is not necessary to remove the bottom plate in the beginning, and then only to unsolder 1 wire and, at the very end to loosen or remove the battery compartment when the shutter us ready to come out. The mechanism on the bottom of the winding lever shaft can be left untouched. I left the leatherette on until the point, after unsoldering the wires from the circuit board, when I was ready to remove the mirror box.
Throughout the disassembly process I came across gooey foam from the light seals that are in various locations, if yours aren't decayed so much the better, if they are, make sure you have a light seal kit available for the reassembly process.
1 First to come off is the top cover. Set the speed dial to auto and the ASA dial to 200 (or anything that you will remember.) On the right side is the winder lever, everything is right hand thread here (that is opposite to what we are used to - even knowing this I regularly go in the wrong direction and wonder why it doesn't work). There is no way to grip the cover screw , I have been able to use an eraser or other rubber object to unscrew it by using a fair amount of downward pressure, when that doesn't work I drill a couple of little holes and use my spanner wrench on it. Much better than vise grips... and the cover screw then looks like it came from an MX. Then remove the nut, spanner wrench is very useful for this, the winder lever and the spring washer underneath
2 Next the rewinding knob, open the back and place a screwdriver in the fork that turns the film spool, then turn the rewind knob counter counter-clockwise, normal thread. It's a good idea to leave the shaft in place so that you can open the back, otherwise if the back gets closed you can't open it till the top cover is off.
You will need circlip pliers or similar to remove the clip, then the exposure compensation dial, the spring washer and the ASA dial.
3 The top cover will now come off after removing the three screws that hold it on. Watch out for the little plastic "cover frame" (the trim piece between the top cover and the mirror box) on the front and the "shutter button core" which can fall out of the shutter release button.
4 Get out the soldering iron and unsolder only the wires necessary to remove the circuit board. I took several pictures from different angles, to help in reassembly. Some wires can be left in place if they bypass the circuit board. I suggest unsoldering only those that you are sure have to come off, it's easier to reheat the soldering iron later then to find you have unsoldered a connection that could have been left alone. At least on of the flash contacts and the little circuit board to the left of the prism can be left wired to the circuit board.
5 Remove the flash contacts, the afore mentioned little circuit board to the left of the main one, the viewfinder and anything else that would prevent the circuit board, prism and mirror housing from coming out as a unit.