I removed the boards enough to see both sides. Here's what I did:

- remove 4 screws and the bottom cover

- remove 5 mode buttons by prying the retention clips on either side of each button. I've seen replacement buttons so I know how the clips work. Pry one side off the white ramp, then use a flat screwdriver as a crow bar to pull towards the main board the white plastic on the other side while pushing against the black button. The button will be tight in the case as you pull it out while the tabs are deformed over the ramps. Lots of words, makes sense when it's in front of you.

- pull off the pin holding the temp control thumbwheel in place. It has a hex top but it's a friction fit pin.

- pry the two hooks holding the lower end of the thumbwheel frame to the main case.

- pull out the thumbwheel keeping track of the ball bearing (for friction?)

- it takes some wiggling to get the main board out because the part of the main board where the thumbweel rheostat attaches is wedged under some useless part of the case and because the connector pins are a tight fit in their holes in the case. Steady pressure does it.

- the main board will only come out so far because of 3 ribbon cables (fan speed, illumination and daughter board)

- I couldn't find an elegant way to remove the daughter board so I turned 2 small flathead screwdrivers between the case and the back edge of the daugter board to free the tab on the back edge of the daughter board from the slot in the case.

- the daughter board is also held by tabs in the illumination prism at the front of the case. More wiggling and steady pressure releases it.

I haven't figured out how to remove the fan speed sub-board nor the illumination board. There should be enough access to inspect and resolder all the components at this point given the slack in the ribbon cables.

Now, if only I knew what to look for in terms of burned components and bad solder joints

And my apologies if I use PCB terms in the wrong context.

Sixto
95 S420
87 300SDL