ConMed sabre 180, Service Manual

Page: 69 / 72

5-3
5.2.2 Shield
As viewed from the front of the unit with the Top
Cover open, the Shield is mounted with two nuts
along the top edge, one on the left and one on
the bottom. The four Shield mounting nuts may
be removed using a 9/16'' or 14mm nutdriver.
Avoid dropping the nuts into the Base Assembly.
After the nuts are removed, the Shield may be
pulled free from its mounting studs and forward.
A notch on the left side will clear the left hand
Top Cover stud, permitting the Shield to be
removed fully, left side first.
Reinstallation is by the reverse process. Avoid
crushing harness wires with the bottom edge of
the Shield. Install and tighten all four nuts before
returning the unit to service. After the Shield is
secured, check switch A3S1 for correct position
before closing the Top Cover.
5.2.3 A4 Power PWB
The A4 Power PWB, the heatsink and its compo-
nents and the heatsink support brackets are
removed from the unit as a single assembly. Avoid
stressing the PWB/heatsink joint during handling
to prevent breaking bonding wires in heatsink-
mounted components.
To remove the A4 PWB:
1. Disconnect the four connectors to the output
panel, the two ribbon/DIP harnesses on the right
side, the three brown 0.1" harness connectors
central to the PWB, and the two white nylon
power connectors along the rear. These connec-
tors are keyed and labeled to ensure proper recon-
nection, so they need not be marked.
2. Remove the three nylon nuts along the front
edge of the A4 PWB.
3. Remove the two mounting screws at the right
rear corner and on the rear extension between J1
and C4. Do NOT remove the screw which
secures the heatsink angle bracket on the rear cen-
ter edge.
4. Working from the side of the unit, remove
the four screws securing the front and rear of the
heatsink to the Base Assembly.
5. Lay the disconnected harnesses aside. Lift the
A4/heatsink assembly vertically out of the unit.
While the A4 PWB is out of the unit, take advan-
tage of the opportunity to remove any debris
which may have accumulated in the base pan.
Replacement of heatsink-mounted components
requires special care. After the old device is
removed, clear the solder pads fully. Inspect the
heatsink insulators for damage or holes and
replace if necessary. Use only Conmed-specifica-
tion replacement insulator pads to ensure ade-
quate heat transfer and dielectric strength. Form
the leads of the replacement component accurate-
ly such that no stress is transferred to the package
when it's tab is tightened down. Do not solder
the leads until the tab and insulator are securely
mounted to the heatsink. Tighten screws for Q8,
9 and 10 to 3 in-lb; these devices require com-
pression washers to accommodate thermal expan-
sion. The clips for the other three heatsink devices
should be tightened to 8 in-lb.
Reinstalling the A4 Power PWB is the reverse
process. Ensure that all harnesses are clear before
inserting the assembly. After it is set in place,
install all fasteners loosely. Tighten the four
heatsink screws first, then the two rear PWB
mounting screws, and the three front edge nylon
nuts last. If the A4/heatsink assembly is being
installed temporarily, install and tighten the two
metal PWB screws to ensure ground integrity.
After the assembly is mechanically secure, install
all nine harness connectors. All connectors are
keyed to prevent reversal, but take care when
installing the .156'' nylon connectors to avoid get-
ting one pin off to the side.
5.2.4 A3 Controller PWB
The A3 Controller PWB may be removed after
opening the Top Cover and removing the Shield.
Disconnect the two ribbon/DIP harnesses along
the bottom edge, the two discrete harnesses at the
right edge, the harnesses connecting TO-220
devices A8VR1 and A8Q2, the 4-pin dc power
harness and finally the A2 ribbon harness along
the top edge of A3. Then remove the six mount-
ing screws.