Loosen cover screws. They are captive, so when they turn free, they are done.
Slide the case forward about two inches then lift up.
Opening Locked Unit
Place cover on base with about 1" between the rear of the case and the rear of the top cover. The top cover should now slide easily into the case guide at the bottom rear of the case. If your cover is not mating, check this fit.
The floppy may be a bit misaligned, preventing it from easily fitting into the front bezels. This is uncommon, check on whether the floppy is fully seated on the drive shelf.
Weight Transfer Point
This is a closeup on a weight transfer point. Notice the little rubber bumper on top? The four towers on the drive shelf transfer the weight of any monitor directly to the base. No flexing of the planar. Thing of the issues that the 55SX had with monitors on top of the case, pressing down on the drive riser and flexing the planar.
Removing/Installing the Planar
Remove out all adapter cards, pull out the floppy drive, hard drive, and the drive riser card.
On Model 50 remove the hard drive controller card and the exhaust fan assembly.
Locate the drive structure removal tool under the battery/speaker assembly and use it to pull up all of the white plastic snaps (get the one under the speaker assembly too!). Pull the drive structure straight up. If it doesn't come up, check the white snaps again.
On Model 70 you also want to make sure that the case thumbscrew closer to the MCA slots isn't protruding too far in, blocking the drive subassembly from being pulled up:
Unscrew and pull out the PSU.
Remove the screws holding the planar in. There should be only three of them - one in the front of the 16 bit video slot, one to the front left of the video port, and one near the PSU card edge connector.
Remove the three screws at the back of the system unit that hold in the planar EMC shield in place (right above the I/O ports):
Planar Positioning Pin
To show the thoroughness of the design, there is a small 1/8 inch centering pin coming up from the base of the chassis:
This pin precisely mates with a small hole in the planar board (by the big inductor LN2). Its purpose is to ensure correct alignment of the board with the back of the system chassis:
Warning: Especially all you 85/95 veterans, read carefully! Lift the planar straight up, don't angle it! The planar is positioned exactly with a pin at the rear of the case. You may need to put your fingers in the port opening in back and pull up the EMC bezel exerts force on the positioning pin.
When reinstalling a planar, you will know when it isn't fully seated- the screws from the back will be too low to thread into the mounting points.
Think of the engineering. Everything is positioned in relation to the rear of the case (planar and PSU). The planar is positioned pretty close, once down on that pin, the holes through the planar are darned close to dead on aligned with the threaded inserts in the base.
The PSU slides in from one direction, and when it seats on the planar edge connector, it is aligned with the two holes in the back of the case. There is a little wiggle room, but the PSU more or less drops right in.
Love it. Precision where it matters.