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Yorkville Sound • http://www.yorkville.com
is 10 volts across R235 or R236 which is enough to turn on Q210, Q208, and Q207 pro-
viding 7 DC volts to the fan. Further heating the temperature sensors results in a larger
DC voltage across the fan. To lower the dissipation of Q207, D215, D216, ZD205, ZD206
and R226 turn off Q207 and Q208 when the full wave rectified voltage present of the col-
lector of Q207 reaches approximately 45V by robbing current from the base of Q208.
The maximum fan voltage is 20.5 VDC. ZD207 and R228, R229 and R230 provide a cur-
rent limiting function. Figure #4 shows the current through these resistors when there is
12VDC across the fan.
Thermal Shutdown Circuit
The emitter of Q210 in the fan circuit is the measuring point for the shutdown voltage.
As the temperature sensing devices (AS35) that control the fan circuit heat up the volt-
age on the emitter of Q210 rises until at 85 degrees Celsius on the M1126 heatsinks.
The voltage on the emitter of Q210 reaches 18 (85 degrees C) VDC and the amplifier
must be shutdown to protect the output power transistors. ZD202 and D207 become
forward biased and Q203 turns on turning the relay off and muting the audio signal.
After the amplifier cools down the voltage will decrease until Q37 turns off turning the
relay back on enabling the amplifier.
I I d d e e n n t t i i f f y y i i n n g g D D e e f f e e c c t t i i v v e e B B o o a a r r d d s s i i n n t t h h e e A A P P 4 4 0 0 2 2 0 0
STEP 1: VISUAL INSPECTION OF FRONT PANEL AND FAN
• Check to see whether the green power LED is lit. If not, the amplifier has a
power supply (M1127 board), transformer, A.C. switch or line cord problem.
• If the red protect LED stays on or samples off and on, this usually indicates a
problem with the voltage amplifier or current amplifier sections on one or both of
the M1126 boards. Check for misaligned pin connections or see if the ribbon
cables have been cut or pinched through their insulation.
• If the fan is running at full speed at power up this usually indicates a problem
with the fan circuitry on the M1127 board, but it can also be caused by M1126 cir-
cuit problems. A damaged AS35 temperature sensor located under the M1126
heatsinks can cause erratic fan behavior.
• No output on either or both channels could be caused by intermittent push
switches on the input board.
STEP 2: VISUAL INSPECTION OF INTERNAL CHASSIS AND INITIAL TESTING
After removing the lid, look for any signs of smoke, charring or burnt components.
Before powering up replace the burnt components, and check the associated circuitry
for damaged parts. Disconnect one M1127 board and test one board at a time to
reduce the possibility of further damage. Use a variac to slowly increase the 120 VAC
up from 0 volts while monitoring the quiescent current with a meter and the speaker
output with an oscilloscope. Watch the speaker output for large DC offsets, or oscilla-
tion. Watch the meter for large collector currents flowing. Remember under quiescent
conditions, there should only be 3 to 5 millivolts across test points 8 and 9 on the out-
put stage of the amplifier.
550 Granite Court, Pickering, Ontartio CANADA L1W-3Y8
4625 Witmer Industrial Estate, Niagara Falls, New York USA 14305
5
SERVICE MANUAL
Yorkville Sound • http://www.yorkville.com
SPECIFICATIONS
Frequency Response:
+/- 1dB, 20 Hz to 20 KHz
Hum and Noise:
-103 dB below max output RMS voltage, unweighted
THD (1 khz, 4–Ohms):
<0.01%
THD(20Hz – 20kHz, 4–Ohms):
<0.1%
High Pass Filter:
40Hz, 12 dB/octave
Slew Rate:
Power amp section: 25 V/uS, 50 V/uS in bridged mode
Damping Factor:
> 600, 20 Hz - 400 Hz, into 8 ohms.
Crosstalk:
-75 dB below full output at 1khz, -60 dB below full output
(20 Hz - 20 KHz).
Input Impedance:
20 KOhms balanced, 10 KOhms unbalanced
Input Sensitivity:
1.4 VRMS sine wave.
(AP4020: 36 dB, AP4040: 39 dB gain).
Rejection:
CMRR@60Hz: minimum 48dB, typical 56dB
Controls:
Rotary GAIN controls, MONO/STEREO/BRIDGE, FILTER,
and LIMITER switches.
Displays:
2x CLIP, 2x ACTIVITY, PROTECT, POWER ON. (LEDS)
Input Connectors:
2 x XLR, 2 x 1/4" phone (TRS)
Output Connectors:
2 x Binding Post, 3 x Speakon™ SP-4
Turn On/Off transients:
< 15 milliwatt / seconds, 0.5 Wpk. (1s on delay)
Power Consumption:
Typ 1130, Max 1800 Watts
Transformer:
Toroidal
Protection:
Fully protected: DC, LOAD and THERMAL
Cooling:
Aluminum Heatsinks with DC servo–controlled fan (in front, out rear)
Size:
44 cm x 48 cm x 9 cm
17.5 in x 19 in x 3.5 in
2 Rack Spaces
Weight:
43.5 pounds. 19.8 Kilograms
550 Granite Court, Pickering, Ontartio CANADA L1W-3Y8
4625 Witmer Industrial Estate, Niagara Falls, New York USA 14305
SERVICE MANUAL
(DWH)
(DWH) (front panel to binding posts)
5
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