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SERVICE MANUAL

FOR

SUBWOOFER B2-50

Audio Pro AB

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Summary of Contents for B2-50

Page 1: ...SERVICE MANUAL FOR SUBWOOFER B2 50 Audio Pro AB ...

Page 2: ... 2 TROUBLE SHOOTING TIPS 2 1 B2 50 Does Not Work 2 2 Fuses F501 F502 Blow 2 3 Automatic ON OFF Faulty 2 4 B2 50 Goes On and Off Repeatedly with no signal in 3 ADJUSTMENTS 3 1 Bias Adjustment in Power Amplifier 3 2 Negative Output Resistance Rs in Ace Bass Amplifier 4 SPARE PARTS 5 ENCLOSURES 5 1 Circuit Diagram 2 125010 5 2 Component Layout 3 125004 ...

Page 3: ...upplies 40 V to the Power Amplifier and also stabilized 15 V via voItage regulators V101 V103 It is very important that the 15 V tracks the 15 V accurately when power is switched on or off Mistracking can cause transients or oscillations in the electronic circuits To maintain tracking of the 15 V and 15 V when power is disconnected the 40 V must decay faster than the 40 V For this reason the Power...

Page 4: ...V and OFF level 5 V The input pin 5 senses the voltage from Z201 3 2 1 after rectification in D209 and capacitor C206 Transistor V201 drives relay K101 and a red LED indicating ON When toggle switch 5201 is in position AUTO relay K101 is de energized about 5 minutes after the audio signal on left channel input disappears The time delay is determined by C206 and R210 During testing R210 may be shun...

Page 5: ...IN plug J303 pins 1 and 4 or alternatively on speaker plugs J301 J304 are summed by resistors R318 R319 into a first active low pass filter with kneepoint 138Hz and 8dB gain at 100Hz when channels are in parallel The signal from the first low pass filter is passed via a volume control R322 to a second amplifier stage Z301 10 9 8 with 17dB gain 1 4 Filter The signal from Z301 pin 8 test point C pas...

Page 6: ...s the signals in test points E and J The Power Amplifier is of inverting type and also acts as a summing amplifier adding signals F and J Part of the driver current signal is fed back positively through the Power Amplifier which gives the Power Amplifier a negative output resistance Rs The amount of positive feedback and thereby the value of Rs can be adjusted by trimpot Rrs The parallel circuit L...

Page 7: ...signal is rounded off by the diode network so clipping will be soft The differential input stage V503 V506 is supplied via a current generator V504 Transistors V501 V502 V505 form a current mirror so the output stages from V507 V509 are symmetrically driven The output stage is of triple darlington type with transistors V512 V517 AC gain is 1 V508 senses the temperature of the output transistors an...

Page 8: ...hat DC voltages are OK 40 V 40 2 V 40 V 40 2 V 15 V 15 2 V 15 V 15 2 V 2 1 4 To localize the fault connect a signal generator to DIN plug J303 pins 1 and 4 in parallel Set generator to 5mV 100Hz sine wave Turn sensitivity R322 and crossover frequency subwoofer R402 to max clock wise position You should now measure as follows Test Point AC Volts A approx 5mV B approx 13mV C approx 95mV D approx 90m...

Page 9: ...7 V peak to peak Oscilloscope Signal at test point I should be about 20 V DC 2 3 3 Shunt R210 by 100k ohm to shorten off delay Check that ON is actuated when signal from generator exceeds 5mV at 500Hz 2 4 B2 50 Oscillates Between ON and OFF with no audio signal on input 2 4 1 Check DC offset at test point G Should be between 10mV and 100mV If DC offset is outside these limits fault can be in C414 ...

Page 10: ... readjusted Measure the voltage between emitters on V516 V517 no signal on input terminals of B2 50 Adjust trimpot Rqc R525 till voltage reads 22mV This corresponds to a bias current of 50mA Make final adjustment after B2 50 has been ON for a few minutes so the bias current has reached steady state value NOTE When replacing power transistors temperature sensor on V508 heatsink compound and isolati...

Page 11: ...tmeter at amplifier output reads 16dBU 123mV 3 2 4 Reconnect the speaker cable to the circuit board so drivers are connected to amplifier output and adjust trimpot Rrs till voltmeter reads OdBU 775mV NOTE 1 Voicecoils of drivers must be at room tempera ture when Rrs is set NOTE 2 Voltages in 3 2 3 and 3 2 4 are correct Negative output impedance of Ace Bass amplifier makes output voltage larger whe...

Page 12: ...2 6 Check for correct setting of Rrs as follows Push the cone of forward facing driver inwards and release it suddenly Compare the movement of the cone with the curve below and fine adjust Rrs if required ...

Page 13: ... parts for B2 50 can be obtained from the factories or from Distributors and Service Centers per separate listing When ordering spare parts please refer to serial number of B2 50 and component number per diagram 2 125 010 ...

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