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FIGURE 7.
SR107 TOP VIEW, COVER REMOVED
ing the leads from the push-on board terminals S and R,
and removing the four Phillips head screws securing the
board. The rear edge of the board (side nearest the back
panel) can then be raised, tilting the board toward the
front panel until it is in an upright position.
The foil side of board A2 may be made accessible in a
similar manner by disconnecting the lead from the push-
on board terminal A and removing a total of six Phillips
head screws securing the board.
Replacement board assemblies are supplied with a
number of the interconnecting wires already cut to length
and soldered to board terminals. If either of the two
boards in the SR107 are to be replaced, the new board
assembly should be examined first to determine which
leads are already soldered in place. Those leads which
are duplicated on the new board assembly should be un-
soldered at the point of origin and removed from the
chassis along with the board. Note the lead colors and
points of connection before unsoldering to avoid con-
fusion when installing the new board. Refer to the Circuit
Diagram, Figure 11 for lead identification.
Transistor, Diode and LED Removal
All transistors and diode rectifiers used in the SR107
are mechanically supported by their leads. When replac-
ing these devices, proper lead configurations must be
followed. Minimum soldering heat (preferably with a low-
wattage soldering iron) should be used to avoid damage
to the device. Transistor lead codes are included in the
Notes to Circuit Diagram (Figure 8).
To replace light-emitting diode (LED) D6, mounted on
the front panel, use a long-nose pliers to remove the
mounting ring from the rear of the LED. Press against
the front-panel projection of the LED lens to force it out
the back through the mounting clip. Disconnect the gray
and orange leads from push-on terminals G and E,
respectively, on printed circuit board A1 and remove the
defective assembly.
To install the new assembly, insert the LED in the
mounting collar in the front panel. Slide the mounting
ring over the leads and push it firmly onto the mounting
collar, securing the LED in the panel.
The Shure replacement LED is supplied with gray and
orange leads attached. Thread the leads through the
grommet in the shield separating the power supply from
the signal circuit components. Connect the gray lead to
terminal G and the orange lead to terminal E on board
A l .
Active Component Checking
Defective transistors and diode rectifiers may be lo-
cated by use of a standard ohmmeter such as a Simpson
260. Polarity of the ohmmeter must be verified before
these checks are made.
With a known diode orientation, measure the diode
resistance in the forward and reverse directions. The
lowest meter reading will establish the "minus" probe
while the other probe will be "plus." Some ohmmeters
are not polarized in this manner with relation to "volts
plus probe" and "volts minus probe." With the ohm-
meter "plus" probe on the anode end of a diode and the
"minus" probe on the cathode end, the ohmmeter should
read approximately 2000 ohms or less. With the meter
probes reversed, a reading of about 10,000 ohms or more
should be obtained. If either of these conditions is not
met, the diode should be replaced.
To check transistors, the ohmmeter should be set to
the 100- or 1,000-ohm scale. Transistors and diodes must
be removed from the circuit before testing. If all condi-
tions in the following table are met, the transistor may
be considered free of any major defect; if any of the
following conditions are not met, the transistor should be
replaced. See Notes to Circuit Diagram (Figure 8) for
transistor lead codes.
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