2 FAULT FINDING
A4-14 does not work
2 Set auto ON/OFF in position on
2.1 Check that both the green & red LED are lit.
2.2
Check the power fuses & fuses F601, 602, 701, 702.
2.3
Measure supply voltages +33v ±2.5V, -33v ±2.5V,
+15v ±2V, -15v ±2V
2.4 To localise the fault, connect test instruments as
follows:
-Tone generator to J301 pins 3 & 5. Adjust till B
is 42mV. Sensitivity in Max position, bass &
treble pots in centre position. Compare to
voltage levels according to values in circuit
diagram.
2.5 If fuses F601, 602, 702 blow during
measurement per Section 1.4, you may
disconnect the woofers & replace midrange
driver & tweeter by 5-10Ω resistors. Test again
per Section 1.4 (signal levels in points , , , Ⓔ Ⓕ Ⓖ
& will of course be different). Ⓚ Ⓙ
2.6 Auto ON/OFF can also be tested with set-up per
1.4.
-Set auto ON/OFF in AUTO. The signal at 2201
pin 1 should be 7V
p-p
, & the signal Z201 pin 7
should be 15V
DC
.
Relay K101 Should close at 15mV/500Hz in
(R210 may be shunted by 100kΩ to reduce the
off delay)
3. ADJUSTMENTS
3.1 Bias Current In Power Amplifiers
After replacing any output transistor in any of the
power amplifiers, the bias current must be
readjusted. Setting of bias current should be done
while heatsinks are at room temperature, that is
immediately after A4-14 is turned on.
Set potentiometer R722 or R617 till DC voltage
between emitters of V710, V711 reads 10mV Or
voltage between V610, V611 reads of 20mV,which
corresponds to 23mA bias current.
NOTE: When output transistors are replaced, heat
sink compound must be applied to both sides of the
insulation washers & to the temperature
compensating transistors.
Check that insulation is adequate & that the power
transistors are mounted flat against the heatsink.
The heatsink must be screwed on to the PC card
before the transistors are soldered in.
3.2 Negative Output Resistance
After replacing a Woofer, or any of the current
sensing resistors R408-R412, the negative output
resistance must be re-adjusted.
The woofers must be properly mounted in the
cabinet, their voice coils must be connected, & the
bass adjustment potentiometer R311 must be in
centre position. Voice-coils must be cold (at room
temperature).
Apply an input signal of 60Hz ±1Hz & adjust signal
generator till test point ( reads 0dB (=0.775V). Ⓖ
Change frequency to 180Hz +3Hz without changing
the signal level of the signal generator, & set
potentiometer R410 till voltage at test point is Ⓖ
-5.5dB (5.5dB below 60Hz),
Go back & forth between 60Hz & 180Hz & readjust
if required until the difference is stable at 7.3dB.
4. SPARE PARTS
Spare parts can be obtained from Audio Pro
Sweden, or from Distributors & Service Centres.
When ordering spare parts, please refer to serial
number of speaker, & component number per
Circuit diagram 2-141504 resp. 5520991-01
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