ALLEN & HEATH GL2 User manual

L2SM2 ALLEN&HEATH
3
CONTENTS
GL2 INTERNAL LAYOUT ......................................................41
GL2 PANEL WIRING D246/1...............................................42
GL2-S FRONT PANEL ..........................................................43
GL2-S REAR PANEL .............................................................44
GL2-S INTERNAL LAYOUT...................................................45
GL2-S PANEL WIRING D327/2 ...........................................46
INPUT PCB LAYOUT FW045D/3 ........................................47
INPUT PCB CIRCUIT D222/1..............................................48
STEREO PCB LAYOUT FW046D/2 ....................................49
STEREO PCB CIRCUIT D223/1..........................................50
GL2 BLOCK DIAGRAM .........................................................51
GL2 GROUP PCB LAYOUT FW047D/2 ..............................52
GL2 GROUP PCB CIRCUIT D224/1....................................53
GL2 MODE SWITCH BLOCK DIAGRAMS............................54
GL2 MASTER PCB LAYOUT FW048D/3 ............................55
GL2 MASTER PCB CIRCUIT D225/1 sheet 1 .....................56
GL2 MASTER PCB CIRCUIT D225/1 sheet 2 .....................57
GL2-S BLOCK DIAGRAM ......................................................58
GL2-S RETURN PCB LAYOUT .............................................59
GL2-S RETURN PCB CIRCUIT C2322/1 sheet 1 ..................60
GL2-S RETURN PCB CIRCUIT C2322/1 sheet 2 ..................61
GL2-S LR PCB LAYOUT .......................................................62
GL2-S LR PCB CIRCUIT C2323/1 sheet 1 ............................63
GL2-S LR PCB CIRCUIT C2323/1 sheet 2 ............................64
POWER UNIT PCB LAYOUT FW049/3 ..............................65
POWER UNIT CIRCUIT D226/3..........................................66
POWER UNIT WIRING D247A/1 ........................................67
POWER UNIT WIRING D247/1...........................................68
SYS-LINK PCB LAYOUT FW050/1 .....................................69
SYS-LINK PCB CIRCUIT D242/1 ........................................70
RIAA PCB LAYOUT & CIRCUIT MBD111/1 ........................71
WARRANTY STATEMENT ...................................................2
INTRODUCTION ...................................................................3
TECHNICAL DESCRIPTION .................................................4
SPECIFICATION & CONNECTIONS ....................................5
REAR PANEL CONNECTIONS ............................................6
INSTALLING THE CONSOLE ...............................................7
EARTHING THE AUDIO SYSTEM ........................................7
INTERCONNECTIONS .........................................................8
ADJUSTING THE LEVELS....................................................8
OPTIONS...............................................................................8
IDENTIFYING THE FAULT....................................................9
SERVICEPROCEDURES.....................................................9
PRECAUTIONS .....................................................................9
TROUBLESHOOTING CHART .............................................10
REMOVING THE BASE.........................................................11
REPLACINGA CHANNEL ASSEMBLY ................................11
REMOVING THE POWER UNIT...........................................12
INPUT CIRCUIT BOARD OPTIONS .....................................13
STEREO CIRCUIT BOARD OPTIONS .................................14
GL2 GROUP CIRCUIT BOARD OPTIONS ...........................15
GL2 MASTER CIRCUIT BOARD OPTIONS .........................16
GL2-S RETURN CIRCUIT BOARD OPTIONS......................17
GL2-S LR CIRCUIT BOARD OPTIONS ................................18
SYS-LINK EXPANDER OPTION FITTING ............................19-26
SYS-LINK OPTION APPLICATION .......................................27-28
RIAA INPUT OPTION FITTING.............................................29-32
FITTING NON-STANDARD FADERS ...................................33-34
DESK STAND FITTING .........................................................35
ORDERING SPARE PARTS .................................................36-38
GL2 FRONT PANEL ..............................................................39
GL2 REAR PANEL.................................................................40
INTRODUCTION
The information presented in this manual is intended for competent technical personnel to carry out service and product
support for the GL2 and GL2-S consoles. We assume that the reader is familiar with the related electronic theory and audio
terminology,andisabletocarryoutbasicservicing, fault-finding and repair of audio equipment ofthistype.Servicepersonnel
should also be familiar with audio system and mains earthing and power requirements, and the associated handling
precautions.
For further information on the operation and application of the GL2 or GL2-S please refer to the GL2 USER GUIDE
publication AP0177 or the GL2-S USER GUIDE publication AP2326 supplied with each console.
Whilstwebelievetheinformationinthismanualtobereliablewedonotassumeresponsibilityforinaccuracies.Wealsoreserve
the right to make changes in the interest of further product development.
SERVICE AND TECHNICAL SUPPORT
Under normal operating conditions the GL2 and GL2-S do not require user maintenance or internal calibration. Any service
work required should be carried out by qualified technical personnel only.
We are able to offer further product support through our worldwide distribution network. To help us provide the most efficient
service please would you quote the console serial number in any communication regarding this product.
SAFETY WARNING !
Mains electricity is dangerous and can kill. Mains voltage is present within the console power unit.
Do not remove the rear cover or internal power unit with mains connected. Check your mains
wiring and earthing before switching on. Refer service work to qualified service personnel only.
Publication:AP0179
Issue2
copyright © 1995 ALLEN & HEATH. All rights reserved

L2SM2
ALLEN&HEATH 4
TECHNICAL DESCRIPTION
The ALLEN & HEATH GL2 andGL2-Soffers the flexible solution to the many requirements of the live sound and
recording environment; whether for conference sound ... in a club ... theatre .. or church ... for touring ... contract
hire ... as well as stereo and multitrack recording. Both versions offer 6 Aux sends switchable in combinations of
pre or post fader, a powerful 4-band 2-sweep equaliser, dedicated stereo channels, and comprehensive monitoring
facilities combine in a compact all metal rack mount chassis to allow total and reliable control of the mixed sound
whatever the application. The GL2 offers 4 sub groups each with 100mm faders, inserts and balanced outputs. It
has a unique switching arrangement which configures the console for Front-of-House or On-stage Monitor
operation, or a combination of both. The GL2-S offers 3 individual stereo outputs each with level control, 6 full
feature stereo inputs and 6 mono inputs.
CONSTRUCTION
All metal chassis for 19" rack mount in 11U space. Comprises a 16swg steel front panel housing individual channel
circuit assemblies interconnected by means of a plug-on IDC harness and single soldered copper wire earth busbar.
The connectors are rear (base) mounted for easy access and space saving in rack or plinth mounted applications.
Access to the internal assemblies is by removal of the 18swg folded steel base. The channel assemblies may be
removed for servicing. The internal power supply unit is a separate module which may be removed for servicing
without theneed toremovethe consolebase. Although the GL2and GL2-Sisdesigned forrackor plinthmounting,
thebaseisangledatthe front and includes tworubber feetto allowthe consoletoadjustfortable-topoperationusing
a suitable rear support. This provides a slope of 14 degrees which allows the rear connectors to clear the mounting
surface whilst minimising the surface area used and providing a hidden or tamperproof connector system.
THE CIRCUIT COMPONENTS
GL2 and GL2-S consoles are manufactured using high performance industry standard linear op-amp, logic gate
and discrete semiconductor circuit designs. The same high quality components as found in top range consoles are
used. In particular the switches, potentiometers and 100mm faders have proven to be durable and problem free.
When operated correctly the normal performance of the console introduces no noticeable audio signal degradation.
THE POWER SUPPLY AND CONSOLE EARTHING
The GL2 and GL2-S uses a universal low noise regulated linear DC supply system for all amplifier, logic and
indicator subsystems. The internal power unit operates from single phase 50/60Hz AC mains input to provide the
three regulated DC outputs required for console operation: +16V (0.5A), -16V (0.5A), +48V (0.05A). The +/-
16V supplies are filtered into separate feeds for the audio and logic/indicator circuits on the individual circuit
assemblies. A high quality low radiation toroidal transformer is wired to suit the local mains supply voltage: 100,
110, 120, 220, or 240 V.AC. The power unit rear panel green LED indicator monitors the pre regulator +/-16V.DC
voltage while the console front panel DC ON indicator monitors post regulators. It is normal for the rear of the
console to run slightly warm as the regulator ICs are insulated and bolted to the power unit chassis which acts as
a heatsink. The console DC input wiring harness is soldered direct to the power unit circuit assembly. There is
enough harness loop to allow removal of the power unit from the console for inspection and servicing. A ground
(earth) lift switch is provided on the rear of the power unit to isolate the console audio 0V from mains earth to avoid
earth loops in situations where multiple earth paths are present, for example in 19" racks where the console is in
contact with earthed rack metalwork. The GL2 and GL2-S chassis metalwork is always connected to the mains
power lead earth connection to ensure operator protection from mains shock. DO NOT REMOVE THE
CONSOLE POWER LEAD MAINS EARTH ! The console audio performance is optimised by using an internal
distributedearthing systemthat separates audioand logic earths. Acopper wire busbaris solderedacross the circuit
assemblies to provide a solid low impedance earth path for the connector 0V returns.
AUDIO INPUTS AND OUTPUTS
The channel mic and line inputs, and main group, L-R and Mono outputs are electronically balanced (differential).
The SSM2142 differential output driver is used to balance the outputs. To use these with unbalanced equipment
the -ve signal should be linked to 0V in the cable or input connector. All console outputs are low impedance and
thus capable of driving several high impedance inputs simultaneously. All inputs and outputs except the group
inserts are in phase.
THE PFL/AFL SYSTEM
The console PFL (AFL) switches send pre-(post)-fade signal to the pfl (AFL) mix busses. This is switched within
the Phones/Monitor circuit by 4053 CMOS gates biased from a +/-7.5V DC supply generated locally from +/-16V.
These gates are switched from the selected monitor source when the PFL or AFL DC buss is switched to 0V. Note
that on GL2 only PFL overrides any selected AFL source.

L2SM2 ALLEN&HEATH
5
FREQUENCY RESPONSE: 20Hz to 20kHz +0/-1dB
DISTORTION:. THD 0.01% Line in to mixoutat1kHz
CROSSTALK: .outputmutebetterthan98dBat1kHz
channelmutebetterthan88dBat1kHz
fadershutoffbetter than 88dBat1kHz
NOISE: ............ 22Hzto22kHz
MICEIN -127.5 dB into 150 ohms
LINEpre-ampat 0dB -88dBu
MIX noise -85 dB ref 0VU
INTERNAL OPERATING LEVEL: -2 dBu
INTERNALHEADROOM: ............ +23dB
MAX OUTPUTS: .......................... balanced +27dBu 600ohms maxload
unbalanced+21dBu 2kohmsmaxload
Allconsoleinputsandoutputsarein-phaseexceptfortheGROUPINSERTSonGL2
METERS: ..................................... Peakrespondingbargraph
0VU=+4dBuat XLR outputs
PEAK LEDs:................................. Turn on5dBbefore clipping
SIG LEDs: (GL2 only) .................. dynamicrespondingTurnonat-20dBu
SPECIFICATION
0 dBu = 0.775 Volts RMS
0 dBV = 1 Volt RMS
POWER REQUIREMENTS: ........ 50/60Hz40Wmax
Mainsvoltagesetforlocalrequirements.
PHANTOM POWER: ................... +48V DC50mA
ChannelXLRinputsindividuallyswitched
DIMENSIONS:
Width............... 19.0" standard 19" rack.......... (483mm)
Height .............. 19.2" 11U rack space............. (488mm)
Depth............... 3.5" ........................................... (90mm)
WEIGHTS:
Unpacked ........ 21lbs ................... (10.5kg)
Packed ............ 28lbs ................... (13kg)
CONSTRUCTION:
Allmetalchassis.
Standard19"rackmountin11Uspace.
Singlefrontpanelwithindividualremovablecircuitassemblies.
Removablebaseforserviceaccess.
Removableinternalpowersupplyunit.
OUTPUTS:
L-R OUT ........................XLR............................ pin 2hot,3coldbalanced .......... 50ohms...........+4 dBu +27dBumax
ST1/2 (GL2-Sonly)..........1/4" JACK .................. tiphot, ringgnd unbalanced ...... 75ohms...........variable +21dBumax
MONO OUT (GL2 only) .. XLR............................ pin 2 hot, 3 cold balanced .......... 50ohms...........+4dBu +27dBumax
GROUP OUT (GL2 only) XLR............................ pin 2 hot, 3 cold balanced .......... 50ohms...........+4dBu +27dBumax
DIRECT OUT .................1/4" JACK .................. tiphot, ringgnd unbalanced ...... 75ohms...........-2dBu .+21dBumax
AUX OUT .......................1/4" JACK .................. tiphot, ringgnd unbalanced ...... 75ohms...........variable +21dBumax
2-TRACK SEND ............RCA PHONO....................................... unbalanced ...... 1kohm.............-10dBV
INSERT SEND...............1/4" JACK .................. tip send, ringretunbalanced ...... 75ohms...........-2dBu .+21dBumax
MONITOR OUT (GL2 only) 1/4" jack ................. tip left,ring rightunbalanced ...... 100ohms.........variable +21dBumax
MONITOR OUT (GL2-S only) RCA PHONO................................ unbalanced ...... 700ohms.........variable +15dBumax
PHONES OUT ...............1/4"jack ..................... tipleft,ringrightforstereoheadphones8to400ohms
INPUTS:
MIC IN ............................ XLR............................ pin 2 hot, 3 cold balanced .......... 2kohms ...........variable-60to-10dBu
LINE IN ..........................XLR............................ pin 2 hot, 3 cold balanced .......... 10kohms ......... variable-40to+10dBu
or 1/4" JACK .................. tiphot,ringcoldbalanced .......... 10kohms ......... variable-40to+10dBu
STEREO IN A ................1/4" JACK .................. tip hot,ringcold unbalanced ...... 20kohms ......... variable-20to+22dBu
STEREO IN B ................RCA PHONO....................................... unbalanced ...... 20kohms .........variable-20to+22dBu
RETURN IN ...................1/4" JACK .................. tiphot, ring gnd unbalanced ...... >10kohms ........variable-10dBVmin
2-TRACK RETURN .......RCA PHONO....................................... unbalanced ...... >6kohms .........-10 dBV
INSERT RETURN..........1/4" JACK .................. tip send,ring retunbalanced ...... >6kohms ......... -2dBu
CONNECTIONS

L2SM2
ALLEN&HEATH 6
GL2-S CONNECTOR PANEL
GL2 CONNECTOR PANEL

L2SM2 ALLEN&HEATH
7
19" rack width Provide adequate space behind the rear of
the console power unit for ventilation.
The panel may feel warm around the
power unit. This is quite normal as the
chassis acts as a heatsink for the internal
power supply components.
11U space
The two M3 base securing bolts each side
align with mounting recesses in the rack
system.
Mounttheconsole using4xM6boltseach
side for maximum strength. These should
beprovidedby the supplier oftherackkit.
The GL2 and GL2-S has two support feet
fitted to the front of the base to set the
correct angle (14 degrees) for table top
operation with adequate clearance for the
connectors. Support the rear of the con-
sole to achieve this angle. Operation in
this way prevents interference with the
connectors and takes up the minimum of
table space.
The height does not include the control
knobs (add 20mm) or connector nuts (add
8mm).
The rack should allow a minimum side to
side clearance of 450mm.
INSTALLING THE CONSOLE
TheGL2 andGL2-S fitsinto an 11Uspacein a standard19" rack system. Alternativelytheconsole may beadapted
for flightcase, plinth or table top operation. Ensure adequate access for installing the connectors on the rear.
Avoid using the console close to strong sources of electromagnetic radiation (e.g. video monitors, high power
electric cabling); this may cause degradation of the audio quality due to induced voltages in connecting leads and
chassis.
EARTHING THE AUDIO SYSTEM
It is well known that many audio installation problems are due to inadequate or incorrect earthing. To ensure the
high level of performance for which the GL2 and GL2-S are designed please note the following:
The console chassis is connected to mains earth via the power cord. FOR SAFETY REASONS NEVER
REMOVE THE EARTH WIRE FROM THE MAINS PLUG. The console audio 0V is connected to mains earth
within the console power unit by the ground lift switch. To prevent mains born and external interference pick-up
on the audio signal it is important that this audio 0V is connected to a good noise-free mains earth, either through
the audio cable screens or by linking to a local earth. Multiple earth paths cause earth (ground) loops which may
result in audible hum and interference. These may be avoided by making sure that there is only one path to earth
from each piece of equipment, disconnecting audio cable screens at one end if necessary.
Selectingthe ground liftswitch on therear of theconsoledisconnects theconsoleaudio 0V fromthe chassis (mains)
earth. This avoids ground loops in situations where the chassis metalwork is in physical contact with another path
to earth, (often the case in 19" rack installations), or if audio 0V connects to mains earth elsewhere in the system.
Ground lift switch located on
rearoftheconsolepowerunit.
Presstodisconnectaudio0V
frommainsearth.
PRECAUTION !
TO AVOID DAMAGE TO THE INTERNAL ASSEMBLIES DO NOT
FIT SCREWS THROUGH THE HOLES IN THE SIDES OF THE
CONSOLE. SECURE TO EXTERNAL BRACKETS OR FITTINGS
THROUGH THE TOP PANEL RACK MOUNTING HOLES.

L2SM2
ALLEN&HEATH 8
INTERCONNECTIONS
Incorrectly or badly made interconnecting cables will cause performance and reliability problems, often difficult
to locate. It is important that the cables are carefully chosen and made. In particular, check the soldering and
insulation of the connectors.
Where possible use balanced connections for the channel INPUTs and GROUP, L-R and MONO outputs to
minimise noise pick-up. Avoid running audio cables near to mains or lighting cables or thyristor dimmer units,
powersuppliesetc.Thesemaycauseaudiblehumand buzz. The use of low impedancesources significantly reduces
interference pick-up. Check the cables for correct wiring to avoid problems with phase reversal and unreliable
connection. The GL2 and GL2-S follow the convention for XLR pin 2 and jack tip = signal hot (+).
Always use balanced cables when connecting to phantom powered microphones.
MAKE SURE THAT THE +48V SWITCHES ARE OFF (FLUSH WITH PANEL) WHEN THE CHANNEL
INPUT XLRS ARE CONNECTED TO NON-PHANTOM POWERED OR LINE SOURCES.
If ground loops cause problems connect the cable screen at one end only as described below. Balanced outputs may
be connected to unbalanced inputs and vice versa by linking the signal cold (-) to 0V ground as follows:
tBalanced output to Balanced input - Connect cable screen at destination only.
tBalanced output to Unbalanced input - Connect screen at source only. Link the -ve output to 0v at the output
connector. On the GL2 and GL2-S the unbalanced 1/4" jack inputs automatically provide this link.
tUnbalanced output to Balanced input - Connect cable screen at destination only. Link the -ve input to 0V
at the input connector. On the GL2 and GL2-S the unbalanced outputs automatically provide this link.
ADJUSTING THE LEVELS
Incorrect matching of the signal levels between equipment in the audio system is recognised as one of the most
common performance related problems reported to service agents. The usual symptoms are excessive background
noise, signal breakthrough or distortion.
For best performance it is important that the console signal levels are adjusted for “normal operating level”. If too
high the signal peaks will be clipped resulting in a harsh distorted sound, and if too low the signal-to-noise ratio
is reduced resulting in excessive background noise (hiss and hum) and signal breakthrough.
For best results operate the console with the output meters averaging ‘0’ or just below and allowing the occasional
high level passage to rise into the red. This results in a nominal console output level of +4dBu with ample internal
headroom of +23dB to allow for the peaks. It is advisable to use an attenuator pad if you are connecting the outputs
toequipment which doesnothaveinput level controlsandoperates at amuchlower level. Simplyreducingthefader
settings (and hence meter levels) to compensate may result in excessive background noise and breakthrough due
tothereducedsignal-to-noiseratio.Thesameappliestotheconsolemonitoroutputusedtochecktheconsolesignals
through headphones or reference loudspeakers. The monitor amplifier should be matched to the console such that
normal control room listening levels are achieved with the monitor LEV control set around position '5' to '7'.
Operating at a lower position, say '2' or '3', degrades the output signal-to-noise ratio and may result in audible hum
and noise.
The console PFL (pre-fade listen) / AFL (after-fade listen) system lets you listen to and check the level of signals
at different points in the signal path without affecting the main outputs. Use the channel PFL switches to set up
theinput levels.Thisoverrides thephones/monitoroutputs withthepre-fader channelsignal(in mono)anddisplays
its level on the monitor meters. Adjust the channel GAIN controls for an average '0' reading on the meters. Use the
aux, group and L-R AFLswitches to check the post master fader mix levels. Adjust the channel faders for optimum
mixlevel. Thenormal operating settingof the fadersis at the'0' position,allowing 10dB ofboost to thetop of travel.
The red channel, group (GL2 only) and L-R (GL2 only) PEAK indicators give instant warning of potential signal
overload. These illuminate 5dB before clipping. Reduce channel gain or fader settings as appropriate. Each Group
fader on the GL2 has a meter ladder showing signal presence (dynamic indication starting at -20dB), 0dB level,
and peak (5dB below clipping).
OPTIONS
The GL2 and GL2-S presents a high degree of flexibility to satisfy most user applications without the need to
reconfigurethe internal assemblies. However,optionsareavailable to furtherextendthe capabilities oftheconsole.
These require access to and reconfiguration of the internal assemblies and should only be carried out by authorised
service agents or qualified technical personnel. These are detailed in the section: CIRCUIT BOARD OPTIONS.
TheSYS-LINK option is also available to link two or more consoles, or to link a GL2to a GL2-S or to a GL4 console
to extend the number of channels feeding the mix. This is detailed in the section: SYS-LINK EXPANDER
OPTION.

L2SM2 ALLEN&HEATH
9
WHEN A FAULT IS SUSPECTED ...
The console is the control centre of the typical audio installation, providing the link between microphones,
instruments and other sound sources, processing devices, amplifiers etc. through a "highway" of interconnecting
cables carrying audio signals, DC power and AC mains voltages. If a problem is reported it is often assumed that
theconsoleisatfault. Ourexperiencehasshownthat most reported problems are related tofaulty cables, equipment
matching and control setting, or faulty external equipment, and not to the console itself which is designed for
continuedfault-freeperformance with nousermaintainance. Itis usual only toreplacewornout electro-mechanical
parts such as faders during the life of the console.
When a problem is reported it is necessary to isolate the location of the fault within the system. Only when tests
have been made to eliminate faults in equipment connected to the console and in the interconnection cables, should
you attempt to repair or report the console as faulty. A TROUBLESHOOTING CHART is included in this manual
to assist you in identifying the more common fault conditions.
Notethatonlytechnicallycompetentpersonnelshouldattemptservice work on this console. Check also thevalidity
of the manufacturers or selling agents warranty. Always quote the console serial number when reporting a fault.
IDENTIFYING THE FAULT
Fault diagnosis is often carried out remotely by telephone with the user who is often non-technical and needs to be
talked through a series of simple tests to identify the symptoms and locate the problem. These include substitution
of cables and equipment inputs and outputs. If the console is still suspected as faulty it is recommended that all its
audio cables are unplugged and a single known good sound source is patched across the channels to test for correct
operation by monitoring the output through headphones. This often eliminates problems with system earthing and
matching with external equipment.
Faults may be of a permanent or intermittent nature. If intermittent try to induce the symptom by flexing cables,
wiggling connectors, selective mechanical vibration or flexure, and thermal (hot, cold) cycling. Use substitution
of known good circuits to aid identification of the faulty circuit.
SERVICE ACCESS AND PROCEDURES
Access to the internal assemblies is by removal of the base. The power unit may be
removedforservicewithoutremovingthebasefirst. Individualcircuitassembliesmay
be lifted for service or removed for replacement. Procedures for base, power unit and
circuit assembly removal follow later in this manual.
Service work is best carried out with the console inverted on a clean work surface
suitably covered to protect the console cosmetics. Ensure adequate lighting. Remove
all debris such as solder, component legs and wire clippings from inside the console,
and check your work carefully before replacing the base. Test for correct operation.
Iftheconsoleistobesentbycarrierweadvisethatyoucheckthepackingforsuitability
first. Use the purpose designed ALLEN & HEATH packing if it is still intact. This
packing is illustrated here for reference.
PRECAUTIONS
lCheck the console for correct mains voltage connection before switching on.
lDisconnect the mains input before removing the base or power unit. Apply caution
when testing the console or power unit with base removed.
lHandle the console and its internal assemblies with care to avoid damage to the
components or cosmetics. Do not lift or balance the panel on the circuit assemblies
with the base removed.
lDo not plug or unplug the internal IDC connectors with power applied.
lCheck the connectors for correct alignment and seating.
lIf replacing or removing the power unit, check the console DC harness wiring for
correct connection to the power unit circuit board.
lCheck the copper wire earth busbar for correct solder connection to all the circuit
boards.
lUse a good small tip soldering iron for circuit board work to avoid track or pad
damage.

L2SM2
ALLEN&HEATH 10
EXCESSIVE NOISE (HISS), BREAKTHROUGH or
DISTORTION:
Incorrect level matching, for example connecting to
a sensitive amplifier.
The main outputs are professional 'high' level =
+4dBu. For connection to low level equipment an
attenuator pad after the output is recommended.
Optimum performance is achieved with the
faders and meters operated around the '0' mark.
Operating the output faders at low settings to
compensate for sensitive equipment degrades
signal to noise performance. The console PFL
system and PEAK indicators allow
comprehensive checking of the console levels.
Balanced output incorrectly wired - excessive hiss
but signal present.
For balanced operation check that both + and -
pins are connected.
For unbalanced operation check that the - pin is
linked to 0V in the plug.
EXCESSIVE NOISE (HUM):
Console 0V not connected to mains earth via a
suitable cable connection.
The console chassis metalwork is connected to
mains earth via the power unit to ensure operator
safety. A ground lift switch is provided to allow
optimum system earthing in a way that best
avoids audible earth (ground) loops. If the 0V to
mains earth path is not made within the console
or system then audible hum or buzz may result.
Earth (ground) loop formed due to multiple earth
paths.
External AC hum field induction.
Console or audio cable positioned too close to the
power supply unit or other AC mains equipment
and cables.
Internal AC hum field induction.
The power unit toroidal transformer should be
rotated to the position which minimises audible
hum on the main console outputs. A mu-metal
shield may be fitted to reduce this.
EXCESSIVE NOISE (BUZZ):
External computer interference or breakthrough.
Keep the console and audio cable harnesses away
from computer equipment and associated cables,
thyristor dimmer units and lighting equipment.
EXCESSIVE NOISE (CLICKS, THUMPS,
CRACKLES, POPS):
Control clicks and thumps may be due to a poor
local mains voltage supply or due to excessive
circuit DC offset voltages.
Continuous crackles and pops may be due to noisy
ICs, transistors or resistors.
CONSOLE DEAD - POWER INDICATORS OFF:
No AC mains to the console.
Check that AC mains is present and switched to
the console.
Power supply fuse blown.
Replace with correct antisurge type and rating.
Power unit component fault.
Contact service agent.
CONSOLE DEAD - PANEL DC INDICATOR DIM
OR OFF, REAR POWER INDICATOR NORMAL:
Regulated DC supply rail/s failed
Short circuit on DC power rails.
Use an ohmmeter to test for shorts across the
console DC rails.
CONSOLE DEAD - PANEL DC INDICATOR DIM,
REAR POWER INDICATOR DIM:
Incorrect mains input voltage.
Pre-regulator power unit fault.
Contact service agent.
GROUP, L-R OR MONO OUTPUT DEAD:
REV or MONITOR MODE switches not correctly set.
Check switch settings for intended application.
SIGNAL DEAD OR DISTORTED:
Insert not correctly wired, or processing equipment
not switched on.
This may be checked by unplugging the insert.
Worn or faulty Insert jack socket.
With nothing plugged into an Insert the signal is
routed through the jack switching contacts. Check
this by plugging in an unwired 3-pole jack plug
and shorting tip (send) to ring (return).
Internal IDC connector misaligned or not pressed on.
Check and reseat.
Component fault.
Trace the signal through the channel path.
LOW LEVEL POOR QUALITY SIGNAL:
'One legged' signal connection.
Check the cables for correct wiring. For balanced
signals both the + and - signal should be connected
to the related input or output + and - terminals. For
unbalanced signals the - terminal should be linked
to ground. GL2 and GL2-S unbalanced jack
connectors do this automatically. Operating with
either the + or - signal unconnected will result in
6dB less level ad a loss of signal quality.
FADER INTERMITTENT OR NOT OPERATIONAL:
Fader mechanically worn or broken.
Replace fader.
Fader track contaminated with dirt or liquid residue.
Replace fader. Do not clean the track with spray or
other electrical cleaner.
The following chart is a guide to the more common fault conditions which may be reported by the user. These assume that
the user has identified thje console itself as suspect. For other console related fault conditions contact an authorised ALLEN
& HEATH service agent.
TROUBLESHOOTING CHART

L2SM2 ALLEN&HEATH
11
REPLACING A CHANNEL ASSEMBLY
If it is necessary to remove a channel assembly for service or replacement proceed as follows: Pull off the associated knobs.
Remove the potentiometer nuts using an 11mm nutdriver. Avoid scratching the control panel. Remove the ribbon cable
harness. Cutthe solid wireearth busbar eitherside of thechannelto beremovedas shown below. Removethe associated fader
or desolder the fader wires as required.
When replacing the assembly make sure that the potentiometers, switches and LED indicators are correctly aligned with the
slots in the control panel. Check also the correct assignment of the Group and Stereo assemblies. Reconnect the earth busbar
by overlapping the wire where cut and soldering together. Use sufficient solder to ensure good joints.
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CUT EACH
SIDE AT BEND OVERLAP
AND SOLDER
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REMOVE 4x FRONT PANEL
M3 SCREWS
REMOVE ALL THE JACK NUTS
(15mm NUTDRIVER) AND 4AB
CONNECTOR SCREWS (XLRs,
PHONOS) AND D-CONNECTOR
NUTS IF FITTED.
REMOVE 2x POWER
UNIT SIDE M3
SCREWS.
DISCONNECT THE MAINS INPUT,
UNPLUG ALL CABLES AND REMOVE
THE CONSOLE FROM THE RACK OR
CASE.
INVERT THE CONSOLE
AND REMOVE 4x M3
BASE SECURING
SCREWS.
REMOVE 4x FRONT PANEL
SIDE M3 SCREWS AND NUTS
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Œ
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‘‘
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DO NOT REMOVE
THESE 3x POWER
UNIT FIXING
SCREWS.
REMOVING THE BASE
Access to the internal assemblies of the GL2 and GL2-S is by removal of the chassis base from the front panel assembly. The
procedure detailed below also applies to the GL2-S. Only the power unit may be removed with the base in place: see section
REMOVING THE POWER UNIT. Proceed in the sequence as follows:
CAREFULLY LIFT OFF
THE BASE.
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L2SM2
ALLEN&HEATH 12
REMOVE THE 3x REAR
POWER UNIT M3 SCREWS REMOVE THE 2x SIDE M3 SCREWS
PRECAUTIONS! Disconnecttheconsolefromthemainssupplybeforeremovingthepower
unit. Servicing of the power unit should only be carried out by technically competent personnel.
DANGER - HIGH VOLTAGE !
PRECAUTION ! Check that the console DC harness wires are soldered to the
correct power unit pins before switching the console on. Ensure good solder joint. Re-
tin the pins if necessary.
PRECAUTION! Checkthatthepowerunitissetforthecorrectlocalmainsvoltage
supply before switching the console on.
LIFT THE POWER UNIT OUT OF THE BASE. BE CAREFUL
NOT TO TRAP THE ATTACHED CONSOLE DC HARNESS
WHEN REMOVING OR REPLACING THE POWER UNIT.
REMOVING THE POWER UNIT
The power unit is common to both the GL2 and GL2-S. The power unit may be removed for servicing with the base in place.
CONSOLE DC
HARNESS ON
THIS SIDE
Theconsole internal DCharnessconnects the powerunitoutput to thechannelassemblies. The harness runsbetweenchannels
8 and 9 and along the ribbon cable recess to the Master circuit assembly. The wires are soldered to the power unit to ensure
lowimpedanceconnections for powerdistribution. Theharnessallows enough service loopforthepower unit tobeliftedclear
of the console for service work. To replace the unit it is necessary to desolder the wires.
0V GREEN WIRE
+16V RED WIRE
-16V BLACK WIRE
CHS GREEN/YEL WIRE
+48V BLUE WIRE