Remove 3 screws at the back (below the output sockets) and 3 at the front (on the front edge – not on the front panel near the switches).
Note that those at the back are short self-tappers. Those at the front are short metal-threads.
Now on the front panel of the machine, remove 2 screws at the far left. These are long self-tappers.
Remove the rearmost 2 of the three screws on the right. These too are long self-tappers.
Now you should be able to lift up the TR-808 main panel and see the rear side of the main board and the smaller board on the right, which is called (for some obscure reason) the voicing board.
Note the power supply in the middle of the bottom part of the case.
The fuse on the left is mains. It, the nearby connectors and the mains connector block present a serious shock danger when the machine is open. If I have a TR-808 open for testing or repair, I always place some masking tape over these live items – basically over the terminal block and over the left side of the power supply. I take the tape off before reassembling the machine, because it is not likely to stay put.
Remove the six knobs.
Remove the nut and lock washer from the mode switch.
Remove 11 screws in total from the front panel: 3 at the rear, 3 at the front and 5 in the middle. (One is normally hidden by the tempo knob.)
Now you can pull the two circuit boards out as a unit.
Beware of the little felt things disappearing. They are the staple food of the vacuum cleaners which are often observed foraging in a newly opened TR-808.
The board with the 16 tact switches can easily be removed and unplugged. The switches are ALPS type SKHCAB – similar to those in the TB-303 but without a stem. The LED, black actuator and coloured button are generally regarded as a unit, and the LED wires must be de-soldered before you can remove this unit to get at the switch.
Usually, simply desolder the two LED pads and the four switch pads and remove the whole kaboodle as one. Then separate the switch from the rest of the unit.
The LEDs are easy to replace with a standard miniature LED, but the black and coloured plastic actuator/button units are not ALPS and as far as I know can only be obtained as spare parts from Roland.
There is also a metal plate below the main board to shield it from capacitively coupled noise from the power supply.
Thanks to Robin Whittle.