JBL HT PS300 SUB-WOOFER - TROUBLESHOOTING - SCHEMATIC DIAGRAM
JBL HT PS300 _ THX Powered Subwoofer_120V &
230V Versions IRF530_TIP141_TIP146_MJE350_TL071CP
Amplifier Power
RMS........200Watts
Drivers..................Dual
12" with polymer -laminated cones
Inputs ...................THX and
normal line level, high level
Outputs..................High
Level Unfiltered Crossover Frequency........50-120Hz Normal and (continuously
adjustable) High Level Inputs
Frequency Response........25Hz -
crossover point (Determined by crossover setting)
Height...................21¾”
Width...................21"
Depth...................21"
Weight..................67lbs
TROUBLE SHOOTING BEFORE OPENING
Check connections, control settings, driver and other
possible external problems. If there is Output, determine if all controls and
Inputs function properly. Rotate Pots over full range while applying lateral
and vertical oscillating forces to locate possible intermittent function. High
Level Inputs should be tested individually both differentially (signal from
"-" to "+" with normal output) and in common mode (signal
from low level ground to both "+" and "-" shorted together,
giving virtually no output). While passing a signal, corner drop the enclosure
a few inches to expose possible intermittent problems. Check woofer for rubbing
of voice coil or tears in cone or surround. Check cabinet for loose extraneous
articles which may have been pushed into rear port. If LED(s) are flashing at
about 0.5Hz, then one or more of the internal fuses are blown.
Replacing power transistors: Clip all 3 leads near body of
transistor. Remove screw and discard device (keep hardware and insulator). Holding each lead in turn with needle nose
pliers, gently heat and remove cut lead from hole in edge or PCB. Clean insulator and seating area on back of
panel. Coat both sides of insulator with silicon (white) thermal compound
(unless silicone rubber pads are provided), position it centered on back of
device with holes aligned. Insert leads into PCB then place pair over hole in
panel; ensure hole in insulator is aligned. Insert screw from far side, pass
shoulder bushing over screw and carefully seat shoulder in hole in tab, add
flat washer, lock washer and nut (finger tight). Center insulator tighten screw
first then solder all three leads in respective slots with full fillet, being
careful not to bridge pads. Use ohmmeter to verify there is no short from tab
of transistor to panel, or between pads.
Tests
Connect negative lead of DVM to either negative output
terminal near the center of the main PCB. Use an insulated probe for the
positive lead to probe various test points. Take care not to short the probe to
adjacent points on the circuit board. Alternately, unplug both output wires to
woofer and connect to these points: darker colored output wire (blue or black)
is negative. Position a switched “power bar” with the switch in a convenient
location near the edge of the bench well away form the unit so that it can be
reached safely to turn AC power ON and OFF to unit without risk of accidental
contact with exposed areas of assembly.
With "bar" switch OFF, plug amplifier cord into
this controlled "power bar".
Observing appropriate safety procedures, turn
"bar" ON.
With DVM probe, test following voltages:
+V +50VDC±10%
-V -50VDC±10%
A+ +15VDC±10%
A- -15VDC±10%
If any of these is incorrect, switch OFF and investigate
power supply.
If DC is OK, check:
Speaker "OUT" tab > 0VDC ±0.03V
collector tab of Q6 >25VDC (+V+2)
collector tab of Q5 >-25VDC (-V +2)
Troubleshoot power amplifier if not correct.
T urn AC OFF. After 60 seconds connect oscilloscope ground
probe to either negative output terminal near the center of the main PCB.
Connect the positive scope probe to the OUT terminal on the smaller driver
board. Set the oscilloscope controls to
20V/div. (DC) and 50msec/div. No load is needed.
Turn AC ON. Set oscillator for about 42Hz sine wave and
raise output level. Observe output of amplifier rise with oscillator level
until sine begins to compress without distortion symmetrically, at about 3
volts inside +V/-V levels.
If there is no output, carefully probe each IC amplifier
output in signal flow sequence starting from the input, with scope at about
0.5V/div., until the location of signal loss is located.
TURN AC OFF. Wait 60 seconds. Repeat
Flip "Phase" switch and confirm no loss of main
output. With about 10V output, sweep oscillator frequency to verify filter and
EQ functions.
Raise "crossover" to "100Hz" and confirm
change in LPF corner. Operation of "Phase Reversal switch" should be
readily apparent in this mode.
TURN AC OFF. Wait 60 seconds.
In turn, repeat) for Left and Right high level inputs, both
differentially (normal) and common mode (null output). Return to) then move
connections to "output 2", then repeat.
If output transistors or other major components of power
amplifier are replaced, re-test the unit without load using the following
procedure (DO NOT just reapply full AC source). There should be no signal input
for this test.
If a dual tracking, current-limited DC supply is available
(preferable method), attach it to +V, -V and common (WITH AC CORD UNPLUGGED!).
Set current limit to about 1A and slowly raise output voltage to±40V, monitoring
output with DC scope (10V/div). Initially,
output should stay at about zero volts, then deviate a small amount (<10
volts) due to offsets and imbalances, and quickly return to zero. In normal
start up with fast rising voltages, this doesn't occur.
After the fault has been corrected, re-test unit with load
resistor. Attach an 8 ohm 100 watt resistor to speaker wire pair (for channel under
test); re-apply oscillator to Input. Turn unit ON and turn signal source up.
Amplifier should deliver about 60W RMS at 8Ω(about 110W at 4Ω) from a stiff
source of rated voltage at frequencies within its band pass. Turn input down
and disconnect load. There should be no instability or ringing on any of the
output waveforms, unloaded and loaded. If some is observed, check compensation
and gain-setting components, by-pass caps and damping networks (especially
those involving C15, C17 and C12).
Tack a 100 ohm 1/4W resistor in the R185 location. Turn unit
ON; apply input signal. Measure the DC
voltage on pin 8 of IC U11 with the amplifier operating. The voltage should be
approx. -15 Volts, and the oscillator frequency on pin 1 about 93 Hz. Carefully
short pins6&7andobserve the output shuts down within 2 seconds. Remove
short and amplifier output should return. Turn OFF and remove R185 resistor to
restore full 350 second delay.
After repair, inspect for possible safety hazards, including
loose hardware, missing lock washers, correct fuses and lead dress of primary
wires (these must be held in position with cable ties so that they cannot touch
secondary components). With ohmmeter, check that panel is connected to signal
ground. Re-attach speaker wires (if removed) to satellite PCB’s, RED or YELLOW
wires on OUT terminals; BLACK or BLUE connected to ground terminals on main
PCB.
SCHEMATIC DIAGRAM
CLICK ON THE SCHEMATICS TO ZOOM IN
