JBL Northridge E250P Service Manual page 16

E250P
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
OK
yes
Power up with no
signal input
LED RED
OK
yes
Check Q4(E)
TO V-
= 0V D.C.
OK
yes
Use scope to check
switching
frequency U6(7)
100KHz
+/-10% , ~24Vp-p
OK
yes
CLASS D AMP OK
END
FLOW CHART
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
Q18,Q22
Discharge C37,
no
Check fuse
transformer, L4,
rectifier, C6 and C8
no
Check
MUTE(+8V) and
Q24,Q25,Q26
no
Check +/-15V-MOD
+/-15V voltage at
U 6(8),U6(4)
no
OK
yes
I/P:10mv/50HZ
Check +15V/SW
Q4(E) TO V-
15V
no
OK
yes
Check
U7(1) = -58.3V
no
OK
yes
Use scope to
check O/P U7(6)
and GND
143Vp-p square
wave shown
no
OK
yes
Check
L2,L3,C71,C72,
C73,C74
15
Check
FB1,FB2,C45,
C50,C60,C63,
R81,R82
Check
MUTE (-12.9V),
And
Q24,Q25,Q26
Check
U7,Q16,Q17,
Q20,Q21,R87,
D26,D35,C64