JBL PowerBass PB12 Service Manual page 29

PB12
PB12 Testing Procedure (Cont.) (Revision 2 Only)
A. Power Amp Section
Resistance
Check
2. Power Up LED RED
With a 5mV signal to Low level input, LED should change to GREEN
-Voltage measurements (DVM)
LED
RED
GREEN
3. D.C. Operation
-Voltage measurements (DVM) on CLASS D POWER AMP
Between V+
And This
GND
Point
Get this
71.7V
Reading
4. Check Switching Frequency
•
Oscilloscope - USE THE PROBE TIP TO U6(7) TO GND
•
Reading 100kHz +/-10%,24Vp-p
B. Pre Amp Section
Line Level Input Sensitivity
-Set up
Resistance from S+ (SPK O/P) to GND should be >1M Ω (NO LOAD)
Resistance from V+ (C6 P+) to V- (C8 P-) gradually Fully CHARGED should read >10k Ω
Resistance from V+ (C6 P+) to S+ (SPK O/P) should read >1MΩ
Resistance from V- (C8 P-) to S+ (SPK O/P) should read >1M Ω
OP AMP
P-U4(1)
0Vrms
7.13Vrms
Q10(C)
Q4(E) Q1(C)
V- GND
0V -71.7V
Turn level, X'OVER FREQ POT Fully CW and LFE switch off
Generator Set at 200mV@50Hz
Signal to Line level input
P-U4(7)
11.84VDC
-12.93VDC
U7(1) U7(2)
GND GND GND
0V -71.7V -71.5V
29
U7(4) U7(6) U7(7)
GND GND GND
-71.2V 0V 0V
U7(8)
GND
4.65V