JBL PowerBass PB12 Service Manual page 30

PB12
PB12 Testing Procedure (Cont.) (Revision 2 Only)
- Voltage measurements
U2(1) U2(14)
306.9mV 461mV
2. High Level Input Sensitivity
-Set up
-Voltage measurements 15.3V at speaker output
3. Low-Pass
-Set up Set Generator at 200 mV@100Hz
Signal to
Measure voltage at S+ speaker output
-Voltage measurement
X'OVER FREQ. Setting
CW
CCW
4. LFE
-Set up Set Generator at 200mV@200Hz
Signal to
Measure voltage at S+ speaker output
LFE switch Setting
Normal
LFE
See flow chart next page for diagnostics.
OP AMP
U2(8) U3(7) U3(1)
460mV 658mV 628mV
Turn level, X'OVER FREQ POT Fully CW and LFE switch off
Set Generator at 1.3V@50Hz
Signal to High level input
Line
level input
Output
14.03V
4.8V
Line
level input
Output
6V
18.32V
U3(14) U3(8) U5(7)
598mV 2.326V 2.02V
30
SPEAKER
U5(1) O/P
3.57V 23.33V