TEST PROCEDURES
1. Bias Adjustment Setup and Procedure4. Power Output Procedure
1.1 Locate the -85V negative terminal4.1 Connect an 8 ohm, 250 Watt load to
found on the capacitor (C4). See Figure 1the output.
for the location of C4.
4.2 Apply a 1.75Vrms, 1kHz signal to the
Note: The 1801 and very early 1800's hadinput.
two lugs on the caps. One with two or three
wires and one single wire. The later pro-4.3 Turn the gain controls up to the point
duction 1800 had three lugs on the capaci-where the clipping LED's just begin to
tor. Either way the lug with the two or three light up and check the output for 250
wires is the lug to disconnect from thewatts.
capacitor. All other lugs remain.
4.4 Repeat the steps above for a 4 ohm
1.2 Remove the lug with two or three wiresload. The output measurement should be
connected to it.400 watts.
1.3 Connect a 0-200mA meter between5. Harmonic Distortion Procedure
the disconnected lug and the - terminal on
the capacitor C4.
5.1 With the unit connected as in proce-
dure 3, turn the gains up to just before
1.4 Disconnect the PCB that is not beingclipping and check the distortion at the
tested by unplugging the multiple pinfrequencies of 20Hz, 5kHz, and 10kHz.
connector.
5.2 The distortion limits are L.15% from
1.5 Turn the amplifier on with no input20Hz to 5kHz and L.5% from 5kHz to
signal applied and adjust the bias pot (R13)10kHz.
for 90mA with the board cold.
6. Thermal Cutoff Procedure
Note: The PCB must be removed from
the chassis for the bias to be adjusted.6.1 Apply a signal to the unit with the
outputs loaded ( 8 or 4 ohms ). Short one
2. Frequency Response Procedurechannel at a time until the unit goes into
thermal cutoff. The thermal indicator should
2.1 Apply a 1Vrms, 1kHz signal to theturn on and the output of the unit should be
input.off.
2.2 Reference a dB meter to the output.6.2 Disconnect the short from the output.
Wait until the unit comes out of thermal
2.3 Check the response from 20Hz tocutoff. You can speed this process by
20kHz. The response should not exceed ?1cooling the PCB with a fan.
dB. Refer to the response specification on
page 2.6.3 Once the unit is cooled apply a signal
to the channel you had shorted to check to
3. DC Offset Proceduresee if its operational.
3.1 With no signal applied measure the DC6.4 Apply a signal to the other channel and
offset at the output. It should measureshort the output. Wait for the thermal
250mV or less.indicator to come on then remove the short
and cool the PCB.
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ACEC
