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To avoid the possibility of personal injury, remove the power supply from operation before opening the
cabinet. Turn off ac power and disconnect the line cord, load, and remote sense leads before attempting
any repair or replacement.
When replacing any heatsink-mounted components except thermostat, smear a thin coating of heatsink
compound between the component and heatsink. If a mica insulator is used, smear a thin coating of
heatsink compound on both sides of the mica insulator.
Do not use any heatsink compound containing silicone, which can migrate and foul electrical contacts
elsewhere in the system. An organic zinc oxide cream, such as American Oil and Supply Company
Heatsink Compound #100, is recommended.
Most of thc attaching hardware in this unit is metric. The only non-metric (sometimes called English or
inch) fittings are listed below. Be careful when both types of screws are removed not to get them
mixed up.
a. Lock-link/shelf-mounting blocks (4 on rear panel, one at each corner).
b.
Rear-panel fuse holder.
c.
Rear-panel ground binding post.
d.
Strap-handle screws (2).
e.
Screws that secure side chassis to front-frame casting (8, 4 on each side).
f.
Screws that secure front-panel to front-frame casting (4, 2 on top and 2 on bottom).
Top Outside Cover Removal. Remove three screws, the rear handle screw (Phillips, 10x32) and two top-rear corner
screws (Pozidriv, M4x.7) using a Size 1, Pozidriv screwdriver. A Phillips head screwdriver does not fully seat into
Pozidriv screws and risks stripping the heads. Do not remove the front handle screw, as the retaining nut will fall into the
unit. Remove the top cover by sliding it to the rear and lifting at the front.
Bottom Cover Removal. Remove only for repair of main board. Remove two bottom-rear corner screws. (Pozidriv,
M4x.7) and remove the bottom cover by sliding it to the rear. You do not need to remove the unit's feet.
Inside Top Cover Removal. The unit includes an inside cover which secures the vertical board assemblies. Remove the
inside cover for repair but not for calibration. Remove the six mounting screws (Pozidriv, M4x.7) – three on each side and
five board fastening screws (Pozidriv, M4x.7) all on top. Remove the inside cover by lifting at the front edge.
When installing the inside cover, insert it first at the right side. While holding it tilted up at the left, reach through the
cutouts in the cover and fit the top tabs of the A2 control board into the mating slots in the cover. With the top cover in
place reach through the cutout above the A4 power mesh board, align the board-fastening screw holes, and replace the rear-
most screw to secure the A4 board. Press the inside cover down firmly while tightening screws that secure cover to chassis.
Complete the installation by replacing the remaining ten screws. Be careful when replacing printed-circuit assemblies and
covers not to bend any boards or components.
A2 Control Board Removal
After removing the inside cover, remove the A2 board by lifting first at the front edge and than pulling it up and out of the
unit. Two connectors hold the A2 board at its bottom edge.
When installing the A2 board, insert it first at the rear of the unit. While holding it tilted up at the front, fit the A2TB1
terminal strip into the mating cutout in the rear panel. Then lower the A2 board's bottom connectors into the mating
connectors on the main board. Press the A2 board into the connectors.
