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c. Eyelet 4
d. Eyelet 5
e. Eyelet 6
f. Eyelet 7
7. Repeat the process for the right channel PC board, the one closer to the front of
the preamp. As you remove each wire, place a clearly marked masking tape label
on the wire with the number of the eyelet from which the wire was removed.
Don't put too much stress on the selector switch as you remove these wires.
a. Eyelet 1
b. Eyelet 2
c. Eyelet 4
d. Eyelet 5
e. Eyelet 6
f. Eyelet 7
8. You may want to use the Toothpick Trick (see page 20) to clear the solder from
these eyelets. Doing so will make reassembly much easier.
9. Remove the two 6-32 nuts, lock washers, and screws that hold the U-shaped
brackets that retain the circuit boards on the bottom of the chassis.
10. Slowly rotate the bottom of the circuit boards toward the back of the preamp until
the boards are approximately horizontal. Many solid wires remain on the circuit
board, but with care it can be slowly rotated to the horizontal position.
11. You're now looking down on the component side of the left channel circuit board.
Modifying the Left Channel Circuit board
Now it's time for a judgment call. You probably have enough access to the left channel
PCB that you can remove Q4, the metal transistor with the clip-on heat-sink, with no
further disassembly. You can even replace Q4 with the supplied TO-92 transistor and
heat sink with no further disassembly. If however, you are uncomfortable with this, the
following directions may help.
1. Remove the 4 screws that hold the left channel circuit board into the U-shaped
bracket. This should give you enough freedom of motion with the circuit board
that changing Q4 can be fairly easy.
2. To Remove Q4:
a. Slip off the clip-on heat-sink.
b. Desolder each of the three leads in turn.
c. Remove the transistor
3. Preparing for the new Q4 (Figure 1, left channel):
a. Taking each of the three leads in turn, heat the pads on the PCB into which
Q4 was installed. Run a toothpick into the accompanying eyelet from the
component side of the board. This will clear the hole, allowing the new
Q4's leads to be installed. For more information, see page 20.
b. Smear a film of thermal compound onto the T0-92 transistor and insert a
heat sink over its body. Be careful to keep heat sink compound off the
leads.
c. Insert the leads of the MPSW45A transistor into the space for Q4,
matching emitter, base, and collector to the indicated places. Note that the
Page 6 of 20
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