We are unable to send out diagrams from here in the UK. It may be worth trying Mamiya America (mamiya.com) , but be careful when taking the unit apart.... there are loads of ballbearings that fall out if you are not very careful.

By Severi Salminen on Tuesday, November 11, 2003 - 12:08 pm:

I have a small problem with Mamiya RB 67 Pro-S Extension tube No. 1. I'll explain the whole thing in detail to avoid not being understood. Please follow closely:

1. Cock the extension tube No.1 (45mm) for Mamiya RB 67 Pro-S

2. Place it on the table so that the cocking spikes are facing the table and you'll see the side where one attaches the lens to. That is a shiny metal finish as opposed to black finish on the other side.

3. You should see total of 5 screws on the bayonet rim. (On the other side there are total of 13 screws and I'm talking about the side with 5 screws).

4. Between 2 of these 5 screws (the 2 screws that are slightly closer to each other than the rest of the screws) you can see the mechanism that prevents one from removing the lens if the tube is not cocked. The mechanism consists of small rectangular "plate" or "spike" (about 3mm x 5mm) that moves slightly when one cocks or uncocks the tube.

5. When the tube is cocked this "thing" should be retracted from the bayonet rim: you should see it positioned slightly inside the rim. And if you now uncock the tube you can see this thing protrude outside to bayonet rim preventing a lens to be removed (if there was one attached...).

In my case, the thing is _allways_ protruded to bayonet rim basically preventing me from removing a lens from the tube even when the tube is cocked. And the reason is that the screw that secures this mechanism is probably a bit loose - or I think that is the reason. You can't tighten the screw without opening the rim screws first, but you can actually see the tip of this particular screw on the bayonet rim between those same 2 screws.

What I need is the exploded view of the extension tube so that I could open the bayonet rim and tighten this screw. Or a verbal explanation what will happen if I remove those 5 screws I mentioned - and how to safely do that. I live in Finland, Helsinki and I know a few repair shops here, but I'd rather fix this myself as prices are _very_ steep for this kind of work. And I'm curious

I hope you follow this explanation. I wish I had a digital camera ;)