Bose 1800 Manual de servicio - Página 10
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1. Bias Adjustment Setup and Procedure
1.1 Locate the -85V negative terminal
found on the capacitor (C4). See Figure 1
for the location of C4.
Note: The 1801 and very early 1800's had
two lugs on the caps. One with two or three
wires and one single wire. The later pro-
duction 1800 had three lugs on the capaci-
tor. Either way the lug with the two or three
wires is the lug to disconnect from the
capacitor. All other lugs remain.
1.2 Remove the lug with two or three wires
connected to it.
1.3 Connect a 0-200mA meter between
the disconnected lug and the - terminal on
the capacitor C4.
1.4 Disconnect the PCB that is not being
tested by unplugging the multiple pin
connector.
1.5 Turn the amplifier on with no input
signal applied and adjust the bias pot (R13)
for 90mA with the board cold.
Note: The PCB must be removed from
the chassis for the bias to be adjusted.
2. Frequency Response Procedure
2.1 Apply a 1Vrms, 1kHz signal to the
input.
2.2 Reference a dB meter to the output.
2.3 Check the response from 20Hz to
20kHz. The response should not exceed ±1
dB. Refer to the response specification on
page 2.
3. DC Offset Procedure
3.1 With no signal applied measure the DC
offset at the output. It should measure
250mV or less.
TEST PROCEDURES
9
4. Power Output Procedure
4.1 Connect an 8 ohm, 250 Watt load to
the output.
4.2 Apply a 1.75Vrms, 1kHz signal to the
input.
4.3 Turn the gain controls up to the point
where the clipping LED's just begin to
light up and check the output for 250
watts.
4.4 Repeat the steps above for a 4 ohm
load. The output measurement should be
400 watts.
5. Harmonic Distortion Procedure
5.1 With the unit connected as in proce-
dure 3, turn the gains up to just before
clipping and check the distortion at the
frequencies of 20Hz, 5kHz, and 10kHz.
5.2 The distortion limits are ≤.15% from
20Hz to 5kHz and ≤.5% from 5kHz to
10kHz.
6. Thermal Cutoff Procedure
6.1 Apply a signal to the unit with the
outputs loaded ( 8 or 4 ohms ). Short one
channel at a time until the unit goes into
thermal cutoff. The thermal indicator should
turn on and the output of the unit should be
off.
6.2 Disconnect the short from the output.
Wait until the unit comes out of thermal
cutoff. You can speed this process by
cooling the PCB with a fan.
6.3 Once the unit is cooled apply a signal
to the channel you had shorted to check to
see if its operational.
6.4 Apply a signal to the other channel and
short the output. Wait for the thermal
indicator to come on then remove the short
and cool the PCB.