b. General Access. For calibration and many servicing procedures, you need
only remove the top cover of this device. For greater accessibility, however, the front
panel should also be disengaged. When disassembling, snap open all cable clamps
before removing any wires.
(1) Top cover. The top cover is secured by six screws: three located along
the rear lip and three along the top edge. Remove these and lift off the top panel.
Insert and tighten each screw when reassembling.
(2) Front panel. Take the following steps only to disengage the front panel
from the model 306 case. Additional steps to "electrically" disconnect the front panel
are contained in the next paragraph below. Do not disengage the front panel to perform
calibrations. When ribbon cables P1 and P2 are disconnected, the on/off time circuits
cannot be adjusted.
(a) To disengage the front panel, disconnect ribbon cables P1 and P2
from their respective PCB jacks. Disconnect the vacuum tubing attached to the rear of
the vacuum gauge. The front panel is secured by seven screws located at each front
corner and three across the front-bottom edge (access from underneath). The front
panel can now be pulled away from the chassis and positioned flat (on its facing
surface). The front panel is still attached to the chassis by the wire harness service loop
and ribbon cable P3. All sub-assemblies may be serviced or removed with the front
panel in this position.
(b) To reassemble, carefully reposition the front panel in place and
secure it tightly with the seven screws. Connect the two pieces of vacuum tubing to the
rear of the vacuum gauge and connect P1 and P2 to their respective PCB jacks
(observe pin polarity). See the schematics in figures 2-1 and 2-2 and the printed circuit
board assembly in figure 2-4.
c. Sub-Assembly Access.
(1) Printed circuit board. The Printed circuit board (PCB) is located on the
left sub-side, sub-assembly. Disconnect ribbon cables P1, P2, and P3 from their respective
PCB jacks. Remove the four screws which secure the PCB to the sub-side panel. A green
wire connected to a ring terminal is secured to the sub-side panel by one of these four
screws. Its purpose is to maintain a ground connection with the front panel whenever
the front panel is disengaged for general access. To reassemble, position the PCB over
the four threaded female studs and secure with screws. Make sure the green wire is
secured beneath the lower left-hand screw. Connect P1, P2, and P3 to their respective
PC board jacks (observe pin polarity--see the schematics and PCB assembly figures).