clipj and pop the rotary pot shafts into position. The re-
maining shafts will fall into position. Before snapping the
board into its locked position on the standoffs, check that Use a small screwdriver with an insulated shaft to
the LEDs are aligned with their respective holes. Seat the make this adjustment; hazardous voltages pres- are
board into its locked position. Assemble the washers and ent in the circuitry near R601.
nuts to the phone jacks on the Input Connectors board.
Make sure that the insulating washer is behind the metal
Carefully adjust dc the balance control for 0 Vdc -C20 mV
washer on the HEADPHONES jack. Check that the POWER,
TEMP WARNING, and SHUTDOWN LEDs are in their proper at the output. NOTE: The normal adjustment range of R601
locations. Replace all knobs. is + 1V. If the dc offset exceeds this value, other problems
exist the in circuit.
Equalizer Board (A4): This board is located at the center
of the foil side of the Output Controls board (A9). Removal DC BIAS CURRENT ADJUSTMENT
requires releasing the nylon standoff locking lugs holding Each Power Amplifier (A6) contains dc a bias current
the board in place and pulling the board straight Dis- out. adjustment control (R617, orange) to set the dc idling
connect the wiring harness connectors from J401 and J402. current through output transistors Q612-Q615. This adjust-
Regulated Power Supply Board (AS): Remove this board ment minimizes crossover distortion without drawing ex-
cessive idling power. The bias current should be checked
by disconnecting connectors J7, J8, and J9, and removing whenever any Power Amplifier circuit components are re-
six screws along the edges of the board.
placed. The adjustment should be made after the dc output
Power Amplifier Boards (A6): The two Power Amplifier balance adjustment. Both dc bias current controls are
boards (Model 700) are identical except for mounting accessible from the left-hand side of the console.
brackets. Remove either board by first loosening PC the The dc bias current adjustment is made with all volume
board-fan assembly. This is accomplished by removing controls down and no speaker load. Remove the Power
four screws securing the boards to the bottom panel. Amplifier board shield and connect dc a voltmeter with a
Select the power amplifier be to removed (channel B floating ground across resistor R632 (0.3 ohms, 7W). See
amplifier is toward the front of the console and channel A Figures 28-31.
is toward the back).
Remove the electromagnetic shield (steel) and electro-
static shield (foil) disconnecting by the grounding and lug
disengaging the shields from the nylon standoffs. Discon- Use a small screwdriver with an insulated shaft to
make this adjustment; hazardous voltages are pres-
nect connectors J13 and J14 (for channel J10 B; and J11 ent in the circuitry near R617.
for channel Remove A). three screws from the of edge the
Power Supply board and, using a small Phillips screw-
driver, two screws from the fan.
Starting with the dc bias current control at full counter-
Output Connectors Board (A7): Remove all PATCH clockwise, adjust it for 6 f 2 mV across R632. The same
BLOCKTM jack retaining nuts washers, and remove board voltage should be present across resistors R633, R638 and
connectors J5 and J6 and unsolder three leads (yellow, R639.
green and black) to the MIC OUTPUT jack (PI). The board
lifts straight out of the rear of the cover. DB PEAK INDICATORSIFEEDBACK FINDERTM
Output Controls Board (A9): Remove the knobs from the CALIBRATION
The following calibration procedures should be per-
right side of the front panel. Remove the four screws with
lockwashers and insulating washers, and disengage the formed when parts in the DB PEAK LED strings have been
replaced. The potentiometers on involved board A9 are the
five nylon standoffs securing board the to the front panel. A DB (R916), B DB (R919), FULL WAVE CAL A (R1044),
Remove connectors J3, J4, J22, J23, and J24 J25.
FULL WAVE CAL B (R1045), and FBF (R972). The balance
LED Board (All): This board (two boards in the Model 700) and dB peak calibrations that are follow given for output
can be removed after the Output Controls board (A9) is channel B; the identical steps for channel A use poten-
removed. The LED board is located directly below the tiometers R916 and R1044. All procedures can be per-
equalizer sliders, and can be removed by lifting upward. formed with the cover open the and Output Controls board
DC OUTPUT BALANCE ADJUSTMENT in place (see Figure 1). Note that the first two procedures
apply to the Model 706 and to channel B of the Model 700.
In order to eliminate dc offset at the output, dc balance a
control (R601, blue) has been provided for each Power Full Wave Balance
Amplifier (A6). This control accessible is from the left- 1. Set the console controls to typical settings (orange
hand side of the console. The dc balance should be index marks), the INPUT ATTENuators to 0, and the
checked and adjusted as necessary whenever any Power MASTER controls to 5.
Amplifier circuit components are replaced. dc The output 2. Feed a 1 kHz, 150 mV signal from a low-distortion
balance adjustment should be made before making the dc sine-wave signal generator to a channel input HI IMP
bias current adjustment. jack. With an audio voltmeter connected (without a
The dc balance adjustment is made with all volume con- speaker load) to a SPEAKER B OUTPUT jack, adjust
trols down and no speaker load. Connect a dc voltmeter the B MASTER or signal generator level control for a
(preferably with a 0.1 Vdc full-scale range) across a 10V output.
SPEAKER OUTPUTS jack (J16-J17 for channel A, J18-J19 3. Connect an oscilloscope across test point TP B (right
for channel B). center of A9) and ground (see Figures 18 and 20). |
ACEC
