JBL EON15 Configuration guide

Introduction and General Information
11
This manual has been prepared to assist technicians with the repair and maintenance of
the JBL EON line of portable performance systems.The procedures described in this man-
ual require advanced technical experience and equipment to perform.
WARNING
There are no user-serviceable parts inside these products.Opening these
products or attempting to service may expose the user to electrical shock.
Refer servicing to qualified personnel.
Substitutions
Although many of the electronic components used in these products may be available from
electronic suppliers, some components are JBL replacements only. A product repaired with-
out JBL specified components may not meet the factory specifications.The product war-
ranty may be voided by a repair using unapproved JBL components.
Test Equipment
1) Audio Precision System One, or
Distortion Analyzer
Function Generator
2) 20MHz Oscilloscope
3) Desoldering Equipment
4) Digital Multimeter
5) High Power Load Bank
6) Variac
The complexity of the product under repair requires professional audio service equipment.
Do not attempt to repair this product without this equipment.
Factory Repair
In the U.S. and Canada: In the event that an EON product must be returned to the factory
for service, contact JBL Professional Service at [phone] for return instructions. Do
not return any merchandise without prior authorization.
Outside the U.S.: Contact the JBL Professional Distributor in your area for service
information.

Transducer Repair
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Repair Kits
Part Number Description
C8REON15 LF Cone Replacement Kit, EON15
C2REON15P LF Cone Replacement Kit, EON15P, EON15P-1/230
31385-03 Dust Dome, EON15, EON15P, EON15P-1/230 EON15PAK
D8R2418 HF Diaphragm Replacement Kit, EON15,
EON Power15, EON15P-1/230 (2418H) (315436-001X)
C2REONSUB LF Cone Replacement Kit, EON PowerSub
C8REON10-G2 LF Cone Replacement Kit, EON10
C4REON10P LF Cone Replacement Kit, Power10
No repair kit is available for the 2412H Compression Driver. Entire driver should
be replaced (P/N 125-10000-00X).
No Repair Kit is available for the M115-8 woofer. Entire driver should be replaced (124-
67001-00X)
NOTE: To recone the EON woofers, it is not necessary to disassemble
the enclosure.The woofer can be reconed from the front.
Tools and Supplies
The following items will be required to properly recone the speaker:
Screwdriver
Long-Nose Pliers
Masking Tape
MEK
Utility Knife
Teflon or Orange Stick
Gap Gauges – 0.089" (15" models only - JBL P/N 90075-.089)
0.080" (10" models only - JBL P/N 90075-.080)
An audio function generator is also required for testing purposes.
The entire recone process uses 3M 1300L adhesive. A tube is included with the recone kit.
Additional adhesive may be ordered from JBL, either by the tube (P/N 71715), or by the
quart (P/N 63376).
Cone Replacement Procedure

13
Recone Procedure
1) Remove grille and inspect speaker carefully before disassembly. Look for and record
the following:
A) Model Number, Serial Number, Date Code, Customer, and Complaint
B) Obvious damage or defects
C) Rubbing / Buzzing
D) Damaged dust dome
E) Damaged cone
F) Glue bond, compliance to frame
2) Remove dust dome. Look for and record the following:
A) Voice coil rubbing in the gap
B) Evidence of cone collapse near the voice coil joint
C) Chips in the gap
3) Remove the cone assembly. Look for and record the following:
A) Coil condition: Overheated, rubbing, chip gouges, voice coil date code
B) Coil to cone and spider bond.
C) Bent or broken frame
D) Loose magnet assembly
E) Foreign material in the gap
F) Check gap concentricity with appropriate gap gauge. Be sure to check
both upper and lower gaps
4) Remove and discard the grille standoffs.
5) Cover magnet gap with tape. Scrape and sand compliance land and spider land until
clean and flat.
6) Clean all dust and dirt from speaker. Clean compliance land and spider land with MEK
or acetone.
7) Remove tape from gap and clean magnet gap with masking tape and with MEK and
a rag.
8) Unpack recone kit and inspect for damage.
9) Verify that the voice coil impedance is correct for the model under repair. 8 ohm voice
coils have a blue mark near the leads, and are used in the passive models ONLY.
10) Place Mylar tube inside the voice coil.
11) Test-fit the cone assembly to the speaker frame. Make sure the tinsel leads are
aligned with the proper terminals, and the scallops in the compliance are aligned with the
bosses on the compliance land. It may be helpful to mark the uppermost scallop. Remove
the cone assembly.
12) Apply a 3/16" (4.75mm) bead of glue to the frame at the spider land. Apply another
bead of glue to the inner edge of the compliance land.
13) Install the cone assembly, maintaining proper alignment of the leads and scallops.
14) Press the surround into the glue with Teflon or orange stick.
15) Allow at least 30 minutes for adhesive to set.
16) Press the surround into the glue again.
17) For best results, allow 24 hours to dry.
18) Remove Mylar tube from voice coil.
19) Using pliers, connect 2 tinsel leads to the terminals.

14
20) Carefully position dust dome on cone.
21) Apply a heavy bead of glue around the dome.
22) Allow 30 minutes for adhesive to set, then apply another bead of glue around
the dome.
23) Install the new grille standoffs into the frame.The long standoffs are for the top holes.
24) Install the grille, using the 4 original screws.
25) Test speaker (See Test Specifications).
26 Inspect and clean the speaker. Return to service.
For EON15, EON Power15 and EON15P-1/230
NOTE:YOU MUST REMOVETHE BAFFLE FROMTHE CABINET. USE CAUTION TO
AVOID DAMAGETO THE BAFFLE GASKET AS IT CAN BE REUSED.
Tools Required
1) .040" Pin Gauge
2) #10 Torx Driver
3) Phillips Screwdriver
4) Prying Tool
5) Gap Cleaning Tape
6) High Frequency Test Station
7) Air Gun and Safety Glasses
Procedure
1) Record Model number, Serial number, Date code and compliant for
warranty information.
2) Lay the enclosure face down on a soft clean surface to avoid damage to the grille.The
woofer, or bottom of the product should be towards the front of the service table.
3) Using a Phillips head screwdriver remove the 2 screws holding the handle and remove
the handle. Remove the 16 screws holding the baffle to the rear enclosure.
4) Remove the rear enclosure from the front baffle using a pry tool. Begin by prying at the
bottom of the enclosure directly beneath the center mounting screw holes.
5) Tilt the enclosure away from the baffle so it rests on it's top. Disconnect the transformer
wires from the A.C. input board as you are tilting if these wires are long enough.
6) Pull the lead wires off the compression driver terminals.
Rediaphragm Instructions 2418H

15
7) Remove the rear cover on the compression driver by removing the three(3) TORX head
screws using a #10 TORX driver. Do not discard the cover/screws.
8) Remove the diaphragm assembly from the magnet structure or cover.
9) Identify defect and record Q.A. code per JBL Professional Service Program manual.
10) Check the gap with a .040" gap gauge. Using compressed air and masking or “tuck”
tape, clean the gap thoroughly per JBL Professional rediaphragming procedures.
11) Lay the new diaphragm assembly into the magnetic gap and align the three screw
holes in the top plate with the three openings in the diaphragm assembly. ANY ORIENTA-
TION OF THE THREE HOLES IS ACCEPTABLE.
12) Be sure the diaphragm seats completely against the top plate within the guide pins.
13) Reinstall the rear cover over the diaphragm.Torgue these screws to 14 inch pounds.
14) Test the compression driver for rubs or buzzes using a 2 volt sine wave from 300Hz to
800Hz. If no buzzes are detected, then test at 2V from 1,500 Hz to 20 kHz for full range
operation and audio clarity. It will be necessary to lift the baffle to expose the horn so
listening tests can be performed accurately.
15) Reconnect the high frequency lead wires to the appropriate terminal on the compres-
sion driver.The terminals are polarized so they will fit only one way. Reconnect the trans-
former wires if they were disconnected in step 5 above.
16) Reinstall the rear enclosure on the front baffle (torque to 21 inch pounds) taking care to
ensure that the baffle gasket is not damaged. If the gasket is damaged, replace with PN#
3321167-001 (382-00036-00 for EON 10 and 10P). Reinstall the handle.
17) Perform a complete system test before returning the product to the customer.
A) Initial Setup
Connect board under test to a +/– 15V power supply at the designated connector pins.
Connect Port-one generator (or a function generator) output A to XLR input connector.
Turn generator A off. Place S201 in “Mic” position.
1) Power up board and verify that “Mic” LED, D202, lights.
Signal Input Assembly Trouble-shooting
EON Power15 and EON15P-1/230

16
B) Power Supply Test
Verify that +15V and –15V supplies are at the correct levels.
1) If the LED doesn’t light: Check for shorts from +15V to ground, –15V to ground, and
+15V to –15V. Check for opens on +15V and –15V lines.Verify that D204 - D207 are
not shorted.
C) “Mic” LED Test
Verify that “Mic” LED, D202, Lights.
1) If the voltage across D202 is greater than 3V, replace open LED, D202.
Line Amp level for 1V P/P at XLR input connector. Adjust volume control, P201, fully
clockwise.
D) Gain Test
1) Place S201 in “Line” mode (switch out), Turn on generator A, set frequency to 400Hz
and adjust.
2) Verify that voltage at output, pin 1 of J204 = 800mV P/P (+/– 100mV)
3) Verify presence of 400mV P/P (+/– 50mV) at pin 1 of U202.
4) Remove oscillator connection to XLR input.Verify resistance from pin 2 of J202 to pin 2
of U202 = Pin 3 of J202 to pin 3 of U202 = 24.75K. If not, check for shorted sections of
S201.Verify resistance from pin 2 to pin 1 of U202 = pin 3 of U202 to ground = 10K. If not
check for opens and shorts around U202.
5) Rotate Volume control counter clockwise while monitoring pin 1 of P204.Voltage should
gradually decrease to zero. If the level is intermittent or control does not attenuate, replace
defective P201.
E) Line Amp Frequency ResponseTest
Advance volume fully clockwise and adjust for 800mV P/P at pin 1 of J204. Change Fre-
quency to 20kHz and verify a level of 750mV (+/– 100mV). Change frequency to 20Hz and
verify a level of 750mV (+/– 100mV).
F) Line Amp Common Mode Rejection Test
Set generator output drive to unbalanced. Adjust frequency to 400Hz. Bring volume
control fully clockwise and adjust oscillator output to obtain 10V P/P at pin 1 of J204. Lift
pin on R227 that is closest to J201 and solder it to pin on R226 that is closest to J201.
Reapply power to board and verify that the voltage present at pin 1 on J204 is less that
250mV P/P. Readjust frequency to 20kHz and verify that the voltage present at pin 1 on
J204 is less that 250mV P/P.

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G) Mic Amp Test
Push Mic/Line switch, S201, in. Adjust volume control, P201, fully clockwise. Adjust for
20V P/P at pin 1 of J204.The input level to the board should be 5.6mV (+/– 300uV).
Adjust oscillator for 5.6mV and verify that voltage at pin 1 of U202 is equal to 150mV P/P
(+/– 20mV).
H) Mic Amp Frequency ResponseTest
Adjust for 20V P/P at 400Hz at pin 1 of P204. Adjust frequency to 20kHz and verify 20V
P/P (+/– 1V) at pin 1 of J204. Adjust frequency to 20Hz and verify 14V P/P (+/– 2V) at Pin
1 of J204.
I) Signal Indicator Test
Set oscillator frequency to 400Hz, S201 to “Mic” position (In). Adjust oscillator level for
300mV P/P on pin 1 of U202.Verify that signal LED, D201 is on.Turn off oscillator and
verify that signal indicator turns off.
J) Peak Indicator Test
Set oscillator frequency to 400Hz, S201 to “Mic” position (In), and Volume control, P201 fully
clockwise. Adjust oscillator level for 20V P/P on pin 1 of P204.Verify that Peak LED,
D203, as well as signal LED, D201 are on.Turn volume control down and verify that Peak
indicator turns off.
A) Initial Setup
The easiest way to drive the EON Power15 Main Board is to connect it to a known good
EON Power15 Input Board. Interconnect both boards using a 7-pin cable assembly. Place
the input board in “Line” mode (S201 out). Advance volume control on input board, P201,
fully clockwise. Attach power transformer to J1. If at all uncertain about bias adjustment
being correct, adjust bias control, VR1, fully counter clockwise. Connect the low frequency
output to a 4 ohm load and the high frequency output to a 8 ohm load. Connect Porta-One
generator output A to input board’s XLR connector. Generator output A should be turned off.
B) Main Test Loop
Monitor +15V supply while slowly advancing Variac, that is powering primary of power
transformer. Watch the input watt meter, the input volt meter, and the voltmeter on the
+15V supply.Verify the following:
Amp Assembly Trouble-shooting
EON Power15 and EON15P-1/230

18
Excessive power not pulled. Slowly advance input power (Don’t allow +15 supply to go
higher than 16V). If power pulled is greater that 20W, before reaching 120VAC in, refer
to “Excessive Line Power Test”.
As you ramp out the input voltage, verify that +15V supply stays in regulation. If supply is
non-existent or excessive refer to “+/– 15V Supply Test”.Verify –15V supply is proper, if
not, refer to above test.
Check –V1 (–39V) and +V1 (39V). If non-existent refer to “+/– 39V Supply Test”.
Check –V2 (–77V) and +V2 (39V). If low refer to “+/– 77V Supply Test”.
Verify that “Mute” test point is close to –15V. Remove power to unit and verify mute line
immediately (200mS) goes high (+15). Re-power board and verify mute line initially goes
high and then goes low about 2 seconds later. If any of the above is not true refer to “Ampli-
fier Muting Test”.
C) Confirmation of Low Frequency Chain:
Measure across emitters of Q1 and Q13, for 4mVDC +/– 300uV (20mA). If required adjust
bias pot, VR1. Measure at low frequency amp output (+LF test point) and confirm less than
+/– 50mV of offset.Turn on Generator A and adjust frequency to 400Hz. Adjust Oscillator
amplitude to obtain 60V P/P at amp output.The waveform should be a nice clean sine
wave, with perhaps, a small hint of clipping.The amp will begin to clip at around 62V P/P.
If the amp prematurely clips, verify input to the amp is not clipped.The amp input can be
measured at the junction of R22 and C18.With 60V P/P at the amp output there should be
around 1.9V p/P at the input to the amp. If one or more of the above tests fails. proceed to
“Low Frequency Power Amp Test”.
Adjust oscillator for 1.9V p/P at pin 1 of U2.Verify voltage at input to the filter, pin 1 of J3,
is about 3.5V P/P. If not, proceed to “Low Frequency Filter Test”.
D) Confirmation of High Frequency Chain:
Turn off Generator A. Adjust “High Frequency Level” control, VR201, on signal board, fully
clockwise. Measure at high frequency amp output (+HF test point) and confirm less than
+/– 50mV of offset.Turn on Generator A and adjust frequency to 3kHz. Adjust Oscillator
amplitude to obtain 60V P/P at amp output.The waveform should be a nice clean sine
wave, with perhaps, a small hint of clipping.The amp will begin to clip at around 63V P/P.
Adjust “High Frequency Level” fully counter clockwise and verify that output level reduces
to around 35V P/P (5dB). Re-adjust “High Frequency Level” fully clockwise. If the amp
prematurely clips, verify input to amp is not clipped.The amp input can be measured at the
junction of R50, R51 and R39.With 60V P/P at the amp output there should be around
2.8V P/P at the input to the amp. If one or more of the above tests fails proceed to “High
Frequency Power Amp Test”.
Adjust oscillator for 3.2V P/P at pin 7 of U2.Verify voltage at the input to the filter, pin 1 of
J3, is about 4V P/P. If not, proceed to “High Frequency Filter Test”.

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E) Excessive Line PowerTest
Verify correct polarity and the following parts are not shorted:
C1, C2 (main filters) and D1 D8 (low frequency power amp), D2-D5, C3, C5, C7, C10 (+/–
77V doublers). No section of BR1 (main bridge) should be shorted.Verify that the +15V
and –15V supplies are not shorted. Return to “Main Test Loop” when fault fixed.
Measure across Q1 and Q13 emitters using DC Voltmeter. Slowly ramp up input voltage
never allowing more than 40W to be pulled from Variac.The voltage across the emitters
should be less than 5mV. If excessive refer to “Low Power Amp Test”.
Measure at +HF test point using DC Voltmeter. Slowly ramp up input voltage never allow-
ing more than 40W to be pulled from Variac.The voltage at the output pin, pin 3 of U1,
should be less than +/– 50mV. Monitor the temperature of U1, with your finger.The tem-
perature should warm slightly but not excessively. The Temperature should not rise more
than 10 degrees C after a few minutes of “idle” operation. If any of the above not true refer
to “High Frequency Power Amp Test”.
F) Supply Test
+/– 15V SupplyTest
Slowly ramp up Variac, never allowing the supplies to exceed +/– 16V. Measure +15V
and –15V supplies. Both should be the correct value +/– .5V.
If a supply is very close to ground potential (Less than +/– 100mV check for:
1. shorts on the +/–15V supplies; references Z3 or Z4;
2. open or incorrect reference bias sources R52 and R65;
3. open series pass devices Q18 and Q19;
4. +/– 39V supplies absent, proceed to “+/– 39V Supply Test”.
If supply is out of specification (deviation of more than .5V but not close to ground poten-
tial) check for:
1. incorrect values of Z3, Z4, R52 or R65
2. proper polarity on C32 and C40
3. excessive current being pulled (Do U2-U4 run hot?...etc.)
4. verify that Q18 or Q19 are noted shorted from base to emitter
If supply is high verify that:
1. Z3 and Z4 are of correct value and are not open
2. R52 and R65 are the correct value
3. Q18 is a 2SD1763A and that Q19 is a 2SB1186A
4. Q18 and Q19 are not shorted Base to Collector, or collector to emitter
+/– 39V SupplyTest
Look for open traces between main bridge, BR1, and main filter Capacitors, C1, C2. Look
for open traces between BR1 and power input connector, J1.Verify that BR1 is not open.
Return to “Main Test Loop” after fault found.

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+/– 77V SupplyTest
The low frequency power amp might also be pulling excessive current. Check for correct
value of R4 and R6 (3.3K) and verify 1.5VDC across them when board is powered. Check
for correct value of R5, R9, R21 and R29 (243 ohms) and verify 900mVDC across them
when board is powered. Check for correct value of R18 (100 ohms) and verify 1.1VDC
across it when board is powered. If any of the above is not true proceed to “Low Fre-
quency Power Amp Test”.
G) Amplifier Muting Test
Power up board and measure voltage at junction of D12, R33 and C21.The voltage
should be –35VDC with about 10V of ripple. If voltage is positive check polarity of D12. If
ripple is excessive check values of R33, C21 and R34.
Measure base of Q17.Voltage should be –.6V. If voltage is more than –1V then
D13 is open or reversed biased.The collector of Q17 should be at around +9V.
Turn power off. Q17 base should quickly go to .6V. If less, check R48 value and for
shorted Q17 (base emitter). If greater than .6V check for open Q17 from base to emitter.
Power up board while monitoring collector of Q17. Voltage should ramp from zero to
around 9V in around 2 seconds. If collector remains close to zero check for:
1. collector to emitter short on Q17
2. incorrect value R49
3. shorted TS1 (Thermostat should be open when cold and will close at 80 degrees C)
4. reversed or shorted Z2.
If voltage ramps up higher than 10V check for open or incorrect value Z2, and for an open
Q16 from base to emitter.
Interrupt power while monitoring collector of Q17.The voltage should quickly fall close to
zero volts. If it doesn’t replace open (from collector to emitter) Q17.
Voltage from base to emitter on Q16 should be .6VDC, if less than that, check for proper
value of R36 and from base to emitter short on Q16.
With power applied the collector of Q16 should be close to –15V. After removing power
the collector should go high, if this is not the case check R35, R44, R47 and Q16.
With power applied the collector of Q16 will be at –15V.This will turn on Q15 and bring the
collector of Q15 close to ground.The voltage at the base of Q15 should be around –.6V. If
lower check value of R35 and verify Q15 and D14 are not shorted. After removing power,
base of Q15 should go to around .6V. If greater than .6V replace open D14.
When operating normal the collector of Q15 should be close to ground potential. If not
check R32. If R32 is correct replace open Q15.When power is removed the collector ofQ15
should approach –15V. If collector stays close to ground potential look for short sur

21
rounding Q15 emitter to collector.
With the collector of Q16 low, D15 will be forward biased and pin 8 of U1 will be at around
3V. If voltage at pin 8 of U1 is lower than the 3V, U1 is defective.Verify:
1. correct value of R44
2. D15 is not shorted and oriented correctly
H) Low Frequency Power Amp Test
1. Amp pulls excessive power when board is connected.
Verify correct values of Q1 (2SC3281), Q13 (2SA1302), Q2 (2SD1763A), and Q12
(2SB1186A). Check that D6 and D7 are not shorted and for proper polarity. Look for pos-
ible shorts in the areas where these parts are. All the above parts form the “Current
Amplifier” (Providing current gain). Everything from Q6, Q8 and before, form the “Voltage
Amplifier” (Providing voltage gain).
If output voltage is centered (Close to ground potential), look for shorts to ground on output
leg (+LF test point).
If output voltage is centered (+LF test point), and output leg is not shorted, there could be a
problem with the bias reference. Jumper across C12. Power Unit. If excessive current is
not pulled, bring AC supply to full (120VAC). Measure across R9 and R21.The voltage
across these parts should not be any greater than 2.5VDC. Measure resistance of R9 and
R21, the correct value is 243 ohms. If R9 or R21 value incorrect, or if the voltage across
these parts is excessive proceed to “Voltage Amp Test”. If R9 and R21 testing doesn’t
uncover a problem, and shorting C12 does bring the power consumption to normal, proceed
to “Bias Reference Test”. Remove jumper across C12.
If the output voltage is offset (+LF test point) from ground there could be a problem in the
voltage amp. Jumper across C12 and then bring this point to ground. If the output voltage
centers itself, remove jumper and proceed to “Voltage Amp Test”. If the voltage does not
center, then the problem is in the current amplifier. Check for shorts on all elements (base
to emitter, base to collector, collector to emitter) of Q1, Q13, Q2, and Q12.
2. No output from the amp when driven.
Verify signal at base of Q10. If there is no signal refer to “Low Frequency Filter Test”.
Verify that junction of R32 and Q15 collector is close to ground potential. If not close to
ground potential refer to “Amplifier Muting Test”. If all of the above is OK refer to “Voltage
Amp Test”.
3. Does amp oscillate? Does amp roll off too soon at high frequencies?
Check all components that effect high frequency stability and response: C4, R2 (output
loading), C8, C15 (current amp stabilizers), C14, R15, and C11.

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4. Crossover distortion in output
Refer to Figure A above and note the character of crossover distortion.This is caused by
both halves of the output stage (Q1, Q2 on positive side, and Q13, Q12 on the negative
side) being turned off right around crossover (crossover from positive drive to negative
drive).This actually takes a small chunk (sometimes only visible in distortion waveform)
out of the center of the output waveform.This also causes some harmonic distortion (Note
the curved portions of the “Distortion Waveform”). Remove input signal to amp and mea-
sure DC voltage across emitters of Q1 and Q13. Bias adjustment, VR1, should allow
adjustment from zero volts to well over 10mV. If not proceed to “Bias Reference Test”.

23
5. Excessive Second harmonic distortion in output
Refer to Figure B above and note the character of second harmonic distortion.This is
caused by an imbalance in amplifying capability in either the current amplifier or the voltage
amplifier. Note that the “Distortion Waveform” could also be inverted in relation to above
depending on the polarity of the imbalance. Place a probe on the output of the amp and
adjust for around 40V P/P if the condition of the board allows this much voltage.Visually
note the characteristics of the waveform and then probe on both sides of C12. C12 is
across the input to the current amp. If the waveform visibly appears almost identical (Same
P/P voltage, same waveform shape) then the problem lies in the voltage amp. Proceed to
“Voltage Amp Test”. If there is much difference between the output waveform and the
waveforms measured at C12 there is probably a problem in the current amp.
6. Bias Reference Test
The purpose of the bias reference circuit is to provide bias to the driver and output transis-
tors to just barely turn them on. Q6 is a positive current source and Q8 a negative current
source.The voltage between the collectors of Q6 and Q8 is regulated by the bias reference.

24
A voltage of around .6V is required across the base emitter junction of a transistor to begin
to turn it on. Since a total of 4 junctions are in the current amp (Q2, Q1, Q13, and Q12) the
bias reference needs to have around 2.4V (4 drops) across it to turn on all four transistors
in the current amplifier.
The range of adjustment is very small (Between 1.7V and 2.8V when VR1 adjustment from
stop to stop).The reason the adjustment range is small, is because very little change in
voltage across the reference produces radical bias current changes in the output stage
(Due to the logarithmic relationship between base emitter voltage to collector current).Too
great a range results in a control that is very hard to adjust.
As a transistor heats up it requires less and less base emitter voltage to obtain the same
collector current. If the bias reference voltage remains constant, and the output and driver
transistors begin to heat up, the current amp will draw more and more current, eventually
destroying itself.This is why the reference transistor, Q5 is mounted to the heatsink: As
the outputs (Q1, Q13) and drivers (Q2, Q12) heat up so does Q5.This action regulates the
output bias current and keeps it constant with temperature.
a. Excessive power pulled from AC line.
This is due to excessive voltage across reference.The range (measure across C12)
should be 1.7V to 2.8V. If not check R13, VR1, R14, and Q5.
b. Crossover distortion in output waveform.
This is due to inadequate voltage across reference.The range (measure across C12)
should be 1.7V to 2.8V. If not check R13, VR1, R14, and Q5.
After amplifier heats up, bias current, and power pulled from AC line, increases.
This is due to the fact that the bias circuit not tracking the current amplifier with temperature.
Make sure that all of the transistors, Q1, Q2, Q5, Q12, and Q13, make good thermal con-
tact with the heatsink (Hardware is tight, adequate thermal grease is on devices, insulators,
and heatsink). If all of this is OK replace Q5.
I) Voltage Amp Test
Turn Generator A off. Lift one side of R12. Connect base of Q10 to base of Q11. Power
up amplifier.Verify that the voltage at collector of Q15 is around zero volts. If not, refer to
“Amplifier Muting Test”.
1. Front End and Current Source
Verify 1.2V across anode of D10 to cathode of D11. If incorrect check D10, D11, R32, R31
and Q14.Verify voltage across R31 (600mV).Verify resistance of R31 (620 ohms).
The voltage at the collector of Q14 should be –6V. If the voltage is subsequently lower look
for short from collector to emitter of Q14.

25
The voltage at both bases of Q10 and Q11 should be very close to ground potential and
the emitters should be at –6V.The voltage drop across R23 and R26 should be around
50mV. Both drops should match within +/– 20%. If all above is not correct check Q10,
Q11, R23, and R26.
The voltage drop across R4 and R6 should be 1.5V for both devices +/– 20%. If voltages
not matched, or if they are higher or lower, verify values of R4 and R6 (3.3K), R5 and R9
(243 ohm), and check for open or shorted elements in Q10, Q11, Q4, or Q7.
2. Upper Class A Drive
Verify that voltage across R9 equals 870mV +/– 20%. If incorrect, check Q7 for open or
shorted elements.
Check the voltage at the base of Q6.This should be half way between the positive supply
voltage and the output node.V(base Q6) = (39 +V (output))/2. If the output is offset –10V
the voltage at the base of Q6 will equal (39 –10)/2 = 14.5V. If incorrect, check values of R8
and R10 (33K). If R8 and R10 are correct, replace Q6.
3. Level Shifter
Verify that voltage across R5 equals 870mV +/– 20%. If incorrect, check Q4 for open or
shorted elements.
Verify that the voltage at the emitter of Q3 is .6V. If incorrect, check Q3 and Q4 for shorts
and opens.
Verify that the voltage across R29 and R5 are the same (+/– 10%). If not check values of
R5, and R29 (243 ohms).Verify that D9 isn’t open, shorted or reversed. If the above
checked OK, verify value of R21 (243 ohms), and check Q9.
4. Lower Class A Drive
Verify that voltage across R21 equals 870V +/– 20%. If incorrect, check Q9 for open or
shorted elements.
Check the voltage at the base of Q8.This should be half way between the negative supply
voltage and the output node.V(base Q8) = (–39 +V(output))/2. If the output is offset 10V
the voltage at the base of Q6 will equal (–39 +10)/2 = –14.5V. If incorrect, check values of
R20 and R25 (33K). If R20 and R25 are correct, replace Q8.
Remove jumper across bases of Q10 and Q11. Re-solder lifted end of R12 back into
board.Turn Generator A on and Power up board.Verify that the output is centered and
undistorted.Turn down oscillator and re-connect 4 ohm load. Bring up oscillator level and
verify that the output is centered and undistorted.

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J) Low Frequency Filter Test
Lift one side of C18.Turn on Generator output A, adjust frequency for 1kHz, and adjust
oscillator level to obtain 4V P/P at the input to the filter, pin 1 of J3. Move probe to junction
of R63, R64, and C37.
Refer to Figure 1 above. Note the straight line from 20Hz to 20kHz at 4 volts.This repre-
sents the 4V P/P input signal that was just set up on pin 1 of J3.The curve below this line
represents the transfer function of the first filter section (R63, R64, and C37) when this
section is operating properly.
Sweep the oscillator frequency and note if the readings are reasonably close to the values
indicated in the plot above. (+/– 15%). For example, with a filter that operates normally, the
output will be 2.3V P/P at 20Hz, 2V P/P at 500Hz, 850mV P/P at 2kHz, 300mV P/P at 6kHz
and 90mV P/P at 20kHz.
The first section is a low-pass filter with the half power point at 800Hz. If the response is
incorrect check the values of R63, R64 and C37. If these values are OK, check the values
of C35 - C37, R59, and R60.
After obtaining proper response proceed to following section.

27
Measure the response at pin 1 of U4. Note in figure 2 above that the input voltage has not
been changed. (Voltage at pin 1 of J3).The other curve represents the response at the
output of the second section of the filter.
The second section is a moderate Q (Q equals about 2) high-pass filter at 55Hz. Because
of the moderate Q the filter actually peaks (The 55Hz Peak).
Verify the peak frequency, 55Hz and the peak voltage 5.1V P/P. Also verify voltages at
20Hz, 100Hz, and 1kHz and 20kHz.
If the response is incorrect check values of C35 - C37, and R59, and R60.
After obtaining proper response proceed to following section.

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Measure the response at pin 1 of U3. Note in figure 3 above that the input voltage has not
been changed. (Voltage at pin 1 of J3).The other curve represents the response at the
output of the third section of the filter.
The third section is a low Q (Q equals about .7) high-pass filter at 33Hz.
Verify the peak frequency, 55Hz and the peak voltage 5.1V P/P. Also verify voltages at
20Hz, 30Hz, and 40Hz.
If the response is incorrect check values of C29, C30, C34, R56 and R57.
After obtaining proper response proceed to following section.

29
Measure the response at pin 1 of U2. Note in figure 4 above that the input voltage has not
been changed. (Voltage at pin 1 of J3).The other curve represents the response at the
output of the fourth and final section of the filter.The output is fed to the low frequency
power amp that essentially has a flat response from 20Hz to 20kHz.
The fourth section is a moderate Q (Q is a little more than 1) low-pass filter at 1.4Hz.
Verify voltages at 100Hz, 1kHz, 2kHz. and 4kHz.
If the response is incorrect check values of R53 - R55, C28 and C33.
Reattach lifted lead of C18.
Bias Set Procedure
The following steps are necessary to set the bias on the Power15 amplifier module, PCB
510-00007-XX rev (any).
1. Connect a 4 ohm load (250 watts) to the red and black leads of the amplifier.
2. While maintaining 120VAC, 60Hz, turn the unit on.
3. Set the signal generator to 85 to 200Hz, and to 0.2 Vrms approximately.

30
4. Using a distortion analyzer and an oscilloscope, turn the bias trim pot (VR1) CCW
until distortion spikes disappear, and the THD+N reading is below 0.1%.
5. Turn oscillator off, while keeping the amplifier on.
6. Verify the power is between 10 and 20 watts.
K) High Frequency Power Amp Test
Turn off Generator A.
1. Amp pulls excessive power when board is powered.
If the output of the amplifier, pin 3 of U1, is centered (around ground potential) check for
a short from ground to the output pin, pin 3 of U1. If no shorting problem is found replace
U1.
If the output pin, pin 3, is offset to one of the rails the power consumption should go to
normal idle level (less than 20W) if the 8 ohm load is removed. If it does not, check for
shorting from the output pin, pin 3, to either the +39V or –39V supplies. If not shorted
replace U1.
If the output is offset, and the power consumption goes down to normal with the load re-
moved, check the following:
Verify that the input to the amp, pin 10, is close to ground potential. If not close, check for
shorts surrounding pin 10. If no shorts are found replace U1.
Verify that pin 9 reflects the output offset polarity. The offset should be much greater than
+/– 1V. If not look for shorts surrounding pin 9 and verify values of R38, R40 and C25. If
no problem found replace U1.
2. No output from the amp when driven.
Verify input to the amp on pin 10. If no signal is present verify that there is a signal at pin 7
of U2. If signal is present a pin 7 of U2 verify values of C27, R51, R50 and R39. Look for
shorts at pin 10 of U1 and for shorts at pin 7 of P3. If nothing is found in above testing
replace U1.
The amp should be out of muting.Verify that pin 8 is equal to about –3V. If the muting pin
is substantially lower, replace U1. If the voltage goes higher than around –5V, and the turn
on delay is operating properly (junction of R44 D15 at around –15V), replace U1.
3. Is the gain of the amplifier low or high? (The gain should be equal to 21).The gain from
pin 10 to pin 3 should be around 21.
4. Does the amp oscillate? Verify correct values of R37, C24, C20, R28, C19, and C22. If
all this is OK replace U1.
5. Is output distorted? Verify input to amp, pin 10 is clean. If input is OK replace U1.