JBL Northridge E150P Service Manual page 16

E150P
DETAILED TROUBLESHOOTING (CONT'D)
START
Resistance check
(no load)
between V+ V-,
V+ O/P,V- O/P
and O/P to GND
is > 10K
Power up with no
signal input
LED RED
Check Q4(E)
TO V-
= 0V D.C.
Use scope to check
switching
frequency U6(7)
100KHz
+/-10% , ~22Vp-p
CLASS D AMP OK
CAUTION : SPEAKER OUTPUT IS FLOATING AND IS NOT PROTECTED AGAINST A SHORT
TO GROUND. ALL TEST INSTRUMENTS CONNECTED TO THE OUTPUT MUST
BE FLOATING. ATTACH THE SCOPE PROBE TIP TO S - and REFERENCE
LEAD TO S+.
(A 10mV signal may need from the input to trigger the Switch turn on)
no
Replace
OK
Q18,Q22
yes
Discharge C37,
no
Check fuse
OK
transformer, L4,
rectifier, C6 and C8
yes
no
Check
OK MUTE(+8V) and
Q24,Q25,Q26
yes
no
OK
yes
END
FLOW CHART
Check +/-15V-MOD
check O/P U7(6)
L2,L3,C71,C72,
15
+/-15V voltage at
U 6(8),U6(4)
FB1,FB2,C45,
no
C50,C60,C63,
OK
yes
I/P:10mv/50HZ
Check +15V/SW
Q4(E) TO V-
15V
no
OK
MUTE
yes
Check
U7(1) = -33V
no
OK
Q20,Q21,R87,
yes
Use scope to
and GND
90Vp-p square
wave shown
no
OK
yes
Check
C73,C74
Check
R81,R82
Check
(-10.7V),
And
Q24,Q25,Q26
Check
U7,Q16,Q17,
D26,D35,C64