There are a few hidden screws that are hard to find. Once you get all the screws out, it will come. Just remember that if it's not coming out easily, STOP. There are more screws. Also, the top panel nees to come out too (4-screws). The screws should be the blue tinted ones. Some screws are deeply recessed and will be hard to replace without either a magnetic tipped screwdriver, or using some tape to driver method to retain screw to driver tip during replacement.
I believe there is a free copy someplace but if you want to buy the complete higest quality manual, which includes full disassembly instructions, you can get it from my website:
http://www.analogalley.com/osccart/product_info.php/manufacturers_id/37/products_id/173
I have the M-71 version of the service manual as well, but it's for all practical purposes, the same.