TM 11-6625-2735-14-1
Vertical Preamp Board Removal.
Remove the board as
follows:
1. 475 DM 43 and DM 40 only—Disconnect three
ribbon-cables from the DM 43 or DM 40 Main circuit board.
Remove the screws from the rear of the Main circuit board
chassis and separate the board and chassis assembly from
the instrument chassis.
2. Remove both vertical POSITION control shafts.
This requires a 0.050-inch Allen wrench to loosen the front
setscrew in each coupling.
3. Remove the TRIG VIEW, 100 OR 20 MHz BW control
shaft. Loosen the coupling setscrew with a 0.050-inch
Allen wrench.
4. Remove the INVERT control extension shaft. Insert
a scribe or small screwdriver between the end of the white
plastic switch-shaft and the inside end of the black plastic
extension-shaft and pry gently.
5. Disconnect eight coaxial cables from the front and
back sides of the board and confirm color coding of each
cable with its jack number in the following list. Record any
exceptions to this procedure for reference when
reassembling.
a. Cable to J380 is white with black and brown stripes.
b. Cable to J385 is white with black and red stripes.
c. Cable to J399 is white with a yellow stripe.
d. Cable to J430 is white with a violet stripe.
e. Cable to J405 is white with a blue stripe.
f. Cable to J410 is white with a green stripe.
g. Cable to J400 (back of board) is white with a brown
stripe.
h. Cable to J349 (bottom, back of board, rear of
INVERT switch) is white with a red stripe.
6. Disconnect the delay-line connection on the Ver-
tical Preamp board. This requires the use of a soldering
iron (a 40 to 60-Watt iron works best) to unsolder the
delay-line ground connection.
7. Unsolder the capacitor lead at the Vertical Preamp
board (bottom, back of board, between the rear of the
INVERT switch and J349) using a 15-Watt soldering iron.
8. At the Vertical Preamp board unsolder one end of a
wire braid that connects between the bottom of the
Vertical Preamp and the Main Interface board under the
high-voltage shield.
9. Disconnect three ribbon-cables from the Vertical
Mode-Gain Switch board and confirm the number of wires
in each cable with its plug number in the following list.
Note locations of cables to facilitate correct reinstallation.
a. Disconnect a six-wire cable from P329.
b. Disconnect a seven-wire cable from P160.
c. Disconnect a ten-wire cable from P260.
10. At a feed-through terminal near U120 and U220,
unsolder two 30-ohm resistors that connect each
attenuator to the Vertical Preamp board. Loosen
attenuator screws for clearance if necessary.
11. Remove the Vertical Preamp board mounting-
hardware at eight locations described in the following list.
A small Phillips screwdriver is required.
a. Remove the screw, cabinet-ground spring, and
hexagonal post at center of the board.
b. Remove two screws that mount the board to two
long posts on the main chassis near top and bottom center
of the Vertical Preamp board.
c. Remove three screws that mount the board to the
rear preamp bracket (at left edge of board).
d. Remove two screws at the right edge of the board
(one screw mounts each attenuator chassis to the board).
12. Remove the Vertical Preamp circuit-board, using
care to prevent damage to any of the components as the
board is removed.
To install the Vertical Preamp circuit-board, reverse the
removal procedure.
4-24
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