Lincoln Na5 Service Manual

							E-4THEORY OF OPERATIONE-4
CONTROL, LOGIC AND 
PROCEDURE BOARDS
The logic board interprets and processes the signals it
receives from the various PC boards, switches and con-
trols.  The logic board also houses a DC power supply
(+5 -10) which is derived from the 22VAC received from
the T2 transformer.  This DC voltage is also used on the
procedure board. 
Upon receiving voltage reference level commands from
the procedure and voltage boards, or the user-operated
switches, the logic board sends the appropriate com-
mand signals to the control and power boards to drive
the wire feed motor to the proper speed and direction.
When the start signal is received by the logic board the
power source contact relay (3CR) is energized  along
with the travel relay (2CR) and the flux relay (1CR).  The
inch down and stop switches signal the logic board
which then directs the control and power boards to apply
the appropriate armature and field voltages to the wire
drive motor.  The inch up switch, which is connected
directly to the control board, dictates that the wire drive
motor reverse direction, backing the electrode wire away
from the work piece.  When the welding current closes
the reed switch the logic board directs the procedureboard to proceed from the strike settings to the optional
start board if used, or to the welding wire speed and arc
voltage parameters.
The control board receives information from the logic
board, the procedure board and the tach feedback cir-
cuit.  The control board then applies the appropriate gate
signal to the SCR power supply on the power board.
This variable and regulated DC voltage is applied to the
motor armature thus controlling the speed of the wire
feed motor.  The preset and actual wire feed speed infor-
mation is sent to the speed meter board where it is
processed and displayed on the digital meter.
The procedure board incorporates the many options
available with the NA-5.  The strike and weld controls
are part of the procedure board and are not optional.
The wire feed speed and arc voltage settings for the vari-
ous modes are programmed through the procedure
board and are then sent to the logic, voltage and control
boards at the appropriate times during the welding cycle.
The burnback time is also coupled through the procedure
board.  This control determines the length of time of
burnback delay after the stop circuit is energized.
Depending on the connections on the logic board, it may
also determine the length of time the wire feed motor
reverses after the stop button is pressed.
FIGURE E.4 Control Logic and Procedure Boards
NA-5
NOTE:
Unshaded areas of block logic diagrams are the subject of discussion.
F1
A
R
M
A
T
U
R
E F
I
E
L
D
V
O
L
T
A
G
E V
O
L
T
A
G
E
T1
T2
OPTIONAL
START
BOARD
OPTIONAL CRATER BOARD
OPTIONAL WELD
TIMER
BURNBACK TIMER
VOLTAGEBOARD
METER
BOARD SPEEDVOLT
METER
BOARD
DIGITALMETER DIGITAL
METER
MOTOR
LOGIC
BOARD
CONTROL BOARD
P
O
W E
R
B
O
A
R
D
P
R
O
C
E
D
U
R
E B
O
A
R D
TACH
INCH
DOWN
SWITCHSTOP
SWITCHSTART
SWITCH
WELD 
CURRENT
REED SWITCH
CR
1
CR
2
CR 3
FLUX
RECEPTACLE
TRAVEL
RECEPTACLE
CONTACTOR  CLOSURE (#2 AND  #4)
REMOTE VOLTAGE CONTROL (A, B, C)
WORK SENSING (#21)TACH FEEDBACK (MOTOR RPM)
DC SUPPLY VOLTAGE
10VDC  REFERENCEVOLTAGE
DC  VOLTAGE S
I
G
N
A
LINPUT
POWER
SWITCH CIRCUIT
BREAKER R1(2 OHMS)
MOTOR
G
A
T
E
S
I
G
N
A
L
S
CONTROL
CABLE
RECEPTACLE
TACH FEEDBACK (MOTOR RPM)
115VAC
36VAC (18+18VAC)
22VAC
1
V
A
C 0 D
C
S
U
P
P
L
Y
V
O
L
T
A
G
E
SIGNAL
A
R
C
V
O
L
T
A
G
E S
H
U
T
D
O
W
N A
N
D
INCH
UP
SWITCH STRIKE/WELD PROCEDURE
ENABLE
FIELD
ARMATURE F
E
E
D
E
N
A
B
L
EDIRECTION
ARC VOLTS (SET & ACTUAL)
WIRE FEED SPEED (SET & ACTUAL)
E L E
C
T
ROD E SENSING
(#67)
1
15
VAC
WELDVOLTS SPEED
VOLTSSPEED
STRIKE
115VAC
#31
#32
1/2 AMP F501
SET SPEED
SET VOLTAGE
STARTTIMER
CRATER TIMERF2
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							E-5THEORY OF OPERATIONE-5
OPTIONAL START, CRATER
FILL AND WELD TIMER
BOARDS
When installed, the optional start board
dictates to the procedure board the
starting wire feed speed and arc volt-
age.  This condition can be operator set
for a predetermined period of time.
These parameters can be set either
higher or lower than those of the weld-
ing procedure to control penetration,
bead shape, or other factors at the start
of the weld.  The start circuit becomes
active when the weld current sensing
reed switch is closed.
The crater fill board is used by the oper-
ator to adjust the finishing wire feed
speed and voltage either higher or
lower than the welding procedure for an
adjustable period of time.  This circuit
becomes active when the stop switchis pressed.   This optional feature is
helpful in controlling bead shape and
filling craters at the end of a weld.
The weld timer permits setting of weld
time for an adjustable period of time.
This feature eliminates the need to
press the stop switch.
FIGURE E.3 Optional Start, Crater Fill and Weld Timer Boards
NA-5
NOTE:Unshaded areas of block logic diagrams are the subject of discussion.
F1
A
R
M
A
T
U
R
EF
I
E
L
D
V
O
L
T
A
G
E V
O
L
T
A
G
E
T1
T2
OPTIONAL
START
BOARD
OPTIONAL CRATER BOARD
OPTIONAL WELD
TIMER
BURNBACK TIMER
VOLTAGEBOARD
METER
BOARD SPEEDVOLT
METER
BOARD
DIGITALMETER DIGITAL
METER
MOTOR
LOGIC
BOARD
CONTROL BOARD
P
O
W E
R
B
O
A
R
D
P
R
O
C
E
D
U
R
E B
O
A
R D
TACH
INCH
DOWN
SWITCHSTOP
SWITCHSTART
SWITCH
WELD 
CURRENT
REED SWITCH
CR
1
CR
2
CR 3
FLUX
RECEPTACLE
TRAVEL
RECEPTACLE
CONTACTOR  CLOSURE (#2 AND  #4)
REMOTE VOLTAGE CONTROL (A, B, C)
WORK SENSING (#21)TACH FEEDBACK (MOTOR RPM)
DC SUPPLY VOLTAGE
10VDC  REFERENCEVOLTAGE
DC  VOLTAGE S
I
G
N
A
LINPUT
POWER
SWITCH CIRCUIT
BREAKER R1(2 OHMS)
MOTOR
G
A
T
E
S
I
G
N
A
L
S
CONTROL
CABLE
RECEPTACLE
TACH FEEDBACK (MOTOR RPM)
115VAC
36VAC (18+18VAC)
22VAC
1
V
A
C 0 D
C
S
U
P
P
L
Y
V
O
L
T
A
G
E
SIGNAL
A
R
C
V
O
L
T
A
G
E S
H
U
T
D
O
W
N A
N
D
INCH
UP
SWITCH STRIKE/WELD PROCEDURE
ENABLE
FIELD
ARMATURE F
E
E
D
E
N
A
B
L
EDIRECTION
ARC VOLTS (SET & ACTUAL)
WIRE FEED SPEED (SET & ACTUAL)
E L E
C
T
ROD E SENSING
(#67)
1
15
VAC
WELDVOLTS SPEED
VOLTSSPEED
STRIKE
115VAC
#31
#32
1/2 AMP F501
SET SPEED
SET VOLTAGE
STARTTIMER
CRATER TIMERF2
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							E-6THEORY OF OPERATIONE-6
NA-5
SCR OPERATION
A silicon controlled rectifier (SCR) is a three terminal
device used to control rather large currents to a load.
An SCR acts very much like a switch.  When a gate
signal is applied to the SCR it is turned ON and there
is current flow from anode to cathode. In the ON state
the SCR acts like a closed switch. When the SCR is
turned OFF there is no current flow from anode to
cathode thus the device acts like an open switch. As
the name suggests, the SCR is a rectifier, so it passes
current only during positive half cycles of the AC sup-
ply. The positive half cycle is the portion of the sine
wave in which the anode of the SCR is more positive
than the cathode.
When an AC supply voltage is applied to the SCR, the
device spends a certain portion of the AC cycle time in
the on state and the remainder of the time in the off
state. The amount of time spent in the ON state is
controlled by the Gate.
An SCR is fired by a short burst of current into the
gate.  This gate pulse must be more positive than the
cathode voltage.  Since there is a standard PN junc-
tion between gate and cathode, the voltage betweenthese terminals must be slightly greater than 0.6V.
Once the SCR has fired it is not necessary to continue
the flow of gate current.  As long as current continues
to flow from anode to cathode the SCR will remain on.
When the anode to cathode current drops below a
minimum value, called holding current, the SCR will
shut off.  This normally occurs as the AC supply volt-
age passes through zero into the negative portion of
the sine wave.  If the SCR is turned on early in the
positive half cycle, the conduction time is longer
resulting in greater SCR output.  If the gate firing
occurs later in the cycle the conduction time is less
resulting in lower SCR output.
FIGURE E.4 SCR Operation
CATHODE
ANODE GATE
GATE
INPUT
OUTPUT
NOTE:  AS THE GATE 
PULSE IS APPLIED
LATER IN THE CYCLE
THE SCR OUTPUT
IS DECREASED.
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							NA-5SECTION F-1
TROUBLESHOOTING & REPAIRSECTION F-1
TABLE OF CONTENTS 
-TROUBLESHOOTING AND REPAIR SECTION-
Troubleshooting and Repair ........................................................................\
..............................Section F How to Use Troubleshooting Guide........................................................................\
..............................F-2
PC Board Troubleshooting Procedures ........................................................................\
........................F-3
Troubleshooting Guide ........................................................................\
.................................................F-4
PC Board LED Definitions ........................................................................\
..........................................F-36
PC Board LED Sequence Table ........................................................................\
.................................F-37
Test Procedures ........................................................................\
.........................................................F-38DC Power Supply Test ........................................................................\
............................................F-38
T1 and T2 Transformer Test ........................................................................\
...................................F-42
Voltage Board Transformer Test ........................................................................\
.............................F-45
Wire Feed Drive Motor Test ........................................................................\
....................................F-48
External Resistance Test (Leads #21 and #67) ........................................................................\
......F-50
Out of Voltage Range Shut Sown Test ........................................................................\
...................F-52
Tach Board Feedback Test ........................................................................\
.....................................F-55
VoltmeterAccuracy Test ........................................................................\
..........................................F-57
Wire Speed Accuracy Test ........................................................................\
......................................F-60
Meter Circuit Accuracy Test ........................................................................\
....................................F-64
Replacement Procedures ........................................................................\
...........................................F-71 PC Board(s) Removal and Replacement ........................................................................\
................F-71
Digital Meter and Meter PC Board Removal and Replacement ......................................................F-73
Tach PC Board Removal and Replacement ........................................................................\
...........F-77
Wire Drive Motor Removal and Replacement ........................................................................\
.........F-81
Retest After Repair ........................................................................\
.....................................................F-85
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							WARNING
NA-5F-2
TROUBLESHOOTING & REPAIRF-2
This Troubleshooting Guide is provided to
help you locate and repair possible machine
malfunctions.  Simply follow the three-step
procedure listed below.
Step 1. LOCATE PROBLEM (SYMPTOM).
Look under the column labeled “PROBLEM
(SYMPTOMS)”.  This column describes
possible symptoms that the machine may
exhibit.  Find the listing that best describes
the symptom that the machine is exhibiting.
Symptoms are grouped into the following
categories: wire feeding problems, mode
function problems, function problems and
welding problems.
Step 2. PERFORM EXTERNAL TESTS.
The second column labeled “POSSIBLE
AREAS OF MISADJUSTMENT(S)” lists the
obvious external possibilities that may con-
tribute to the machine symptom.  Perform
these tests/checks in the order listed.  In
general, these tests can be conducted with-
out removing the case wrap-around cover.
Step 3.
RECOMMENDED COURSE OF
ACTION
The last column labeled “Recommended
Course of Action” lists the most likely com-
ponents that may have failed in your
machine.  It also specifies the appropriate
test procedure to verify that the subject
component is either good or bad.  If there
are a number of possible components,
check the components in the order listed
to
eliminate one possibility at a time until you
locate the cause of your problem.
All of the referenced test procedures
referred to in the Troubleshooting Guide are
described in detail at the end of this chap-
ter. Refer to the Troubleshooting and Repair
Table of Contents to locate each specific
Test Procedure.  All of the specified test
points, components, terminal strips, etc. can
be found on the referenced electrical wiring
diagrams and schematics.  Refer to the
Electrical Diagrams Section Table of
Contents to locate the appropriate diagram.
HOW TO  USE TROUBLESHOOTING  GUIDE
Service and Repair should only be performed by Lincoln Electric Factory \
Trained Personnel.
Unauthorized repairs performed on this equipment may result in danger to\
 the technician and
machine operator and will invalidate your factory warranty.  For your sa\
fety and to avoid
Electrical Shock, please observe all safety notes and precautions detail\
ed throughout this 
manual.
________________________________________________________________________\
__
CAUTION
If for any reason you do not understand the test procedures or are unabl\
e to perform the
tests/repairs safely, contact the Lincoln Electric Service Department fo\
r technical trou-
bleshooting assistance before you proceed call 216-383-2531 or 1-800-833\
-9353.
_____________________________________________________________
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							NA-5F-3
TROUBLESHOOTING & REPAIRF-3
_______________________________
CAUTION:
Sometimes machine failures
appear to be due to PC board failures.  These
problems can sometimes be traced to poor
electrical connections.  To avoid problems
when troubleshooting and replacing PC
boards, please use the following procedure:
1. Determine to the best of your technical ability that the PC board is the most likely
component causing the failure symptom.
2. Check for loose connections at the PC board to assure that the PC board is prop-
erly connected.
3. If the problem persists, replace the sus- pect PC board using standard practices to
avoid static electrical damage and electri-
cal shock.  Read the warning inside the
static resistant bag and perform the follow-
ing procedures:
P.C. Board can be dam-
aged by static electricity.
- Remove your body’s stat-
ic charge before opening
the static-shielding bag.
Wear an anti-static wrist
strap. For safety, use a 1
Meg ohm resistive cord
connected to a grounded
part of the equipment
frame.
- If you don’t have a wrist
strap, touch an unpainted,
grounded, part of the
equipment frame.  Keep touching the frame to
prevent static build-up.  Be sure not to touch
any electrically live parts at the same time.
- Tools which come in contact with the P.C.
Board must be either conductive, anti-static or
static-dissipative. ELECTRIC SHOCK can kill.
Have an electrician install
and service this equip-
ment. Turn the input power
OFF at the fuse box before
working on equipment. Do
not touch electrically hot
parts.
- Remove the P.C. Board from the static-
shielding bag and place it directly into the
equipment.  Don’t set the P.C. Board on or
near paper, plastic or cloth which could have
a static charge.  If the P.C. Board can’t be
installed immediately, put it back in the static-
shielding bag.
- If the P.C. Board uses protective shorting
jumpers, don’t remove them until installation
is complete.
- If you return a P.C. Board to The Lincoln
Electric Company for credit, it must be in the
static-shielding bag.  This will prevent further
damage and allow proper failure analysis.
4. Test the machine to determine if the fail-
ure symptom has been corrected by the
replacement PC board.
NOTE: It is desirable to have a spare (known
good) PC board available for PC board trou-
bleshooting.
NOTE: Allow the machine to heat up so that
all electrical components can reach their oper-
ating temperature.
5. Remove the replacement PC board and substitute it with the original PC board to
recreate the original problem.
a. If the original problem does not reap-pear by substituting the original
board, then the PC board was not the
problem. Continue to look for bad
connections in the control wiring har-
ness, junction blocks, and terminal
strips.
b. If the original problem is recreated by the substitution of the original board,
then the PC board was the problem.
Reinstall the replacement PC board
and test the machine.
6. Always indicate that this procedure was followed when warranty reports are to be
submitted.
NOTE: Following this procedure and writing
on the warranty report, “INSTALLED AND
SWITCHED PC BOARDS TO VERIFY
PROBLEM,” will help avoid denial of legiti-
mate PC board warranty claims.
PC BOARD TROUBLESHOOTING PROCEDURES
WARNING
ATTENTION
Static-Sensitive
Devices
Handle only at
Static-Safe
Workstations
Reusable 
Container
Do Not Destroy
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							F-4TROUBLESHOOTING & REPAIRF-4
NA-5
Observe all Safety Guidelines detailed throughout this manual
If for any reason you do not understand the test procedures or are unabl\
e to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you p\
roceed. Call 216-383-2531 or 1-800-833-9353.
CAUTION
WIRE FEEDING PROBLEMS
PROBLEMS
(SYMPTOMS)POSSIBLE AREAS OF
MISADJUSTMENTS(S)RECOMMENDED
COURSE OF ACTION
The wire feeds whenever the input
power switch is in the “ON” position.1.  Check the “Start” switch (S5). Make sure it is not stuck closed.
2.  Check the “Inch Down” switch (S4).  Make sure it is not stuck
closed.
3.  Check the “Inch Up” switch (S3) Make sure it is not stuck closed.
4.  Check to make sure that jumper lead #693 is connected to the
proper pin on the logic board.
See wiring diagram.1.  Check light 7B on the logic board.It should NOT be on.  If light 7B is
ON remove lead #518A from the
“Start” switch.  If the light remains
ON the logic board may be faulty.
If the light goes OFF check the
switch and associated leads.
See wiring diagram and Figure
F.1.
2.  Check light 7J on the logic board. It should NOT be on.  If light 7J is
ON remove lead #592 from the
“Inch Down” switch.  If the light
remains ON the logic board may
be faulty.  If the light goes OFF
check the switch and associated
leads.  See wiring diagram and
Figure F.1. 
3. |Disconnect lead #586 from the “Inch Up” switch.    If the problem
is resolved check the switch and
associated leads.  See wiring dia-
gram.
4.  Check lights 7B, 7J and 7E. They should all be OFF.  If lights
7B and 7J are OFF and light 7E
is ON the logic board may be
faulty. See Figure F.1.
5.  Disconnect plug “A” from the logic board.  If the wire feed stops the
logic board may be faulty.  See
Figure F.1.
6.  If the feed does not stop with plug “A” disconnected, disconnect plug
“E” from the logic board.  If the
wire feed stops with plug “E” dis-
connected the logic board may be
faulty.  If the wire feed does NOT
stop with plug “E” disconnected
the power board may be faulty.
Replace.  See Figure F.1.
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							F-5TROUBLESHOOTING & REPAIRF-5
NA-5
Observe all Safety Guidelines detailed throughout this manual
If for any reason you do not understand the test procedures or are unabl\
e to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you p\
roceed. Call 216-383-2531 or 1-800-833-9353.
CAUTION
WIRE FEEDING PROBLEMS
PROBLEMS
(SYMPTOMS)POSSIBLE AREAS OF
MISADJUSTMENTS(S)RECOMMENDED
COURSE OF ACTION
The wire does not feed.  Pressing
any of the switches (buttons) will
NOT feed the wire.  The motor does
NOT run.1.  Make sure input power switch is ON.
2.  Check the circuit breaker (CB1). Reset if tripped.
3.  Make sure 115VAC is being applied to the control box through
the control cable receptacle.
Leads #31 and #32.
4.  Check the two fuses on the power board.  Replace if blown. If
fuse F101 immediately fails when
replaced  contact your local
Lincoln Authorized Field Service
Facility.
5. Make sure the motor cable is con- nected to the motor receptacle on
the NA-5 control box.  1. Check the lights (LEDS) locate onthe PC boards. Some should be
lit.  See 
Table F.1.If none of the
lights are lit perform the 
T1 and
T2 Transformer Test.
2.  If the appropriate lights are lit (see Table F.1.) and the wire
does NOT feed  perform the 
Wire
Drive Motor Test. 
3.  If only some of the appropriate lights on the power board are lit
the power board may be faulty.
4.  If all of the appropriate lights are lit, except light 1D on the power,
board, check resistor R1.  Normal
resistance is 2 ohms.  See wiring
diagram.
5.  If fuse F101 immediately fails when input power is applied,
unplug all of the PC boards
except the power board.  If the
fuse still fails the power board
may be faulty.   If the fuse does
not fail reconnect the PC boards
one at a time until the faulty
board is located.  Also check and
inspect the wiring harness for
“short” or “grounds”.  Reconnect
the PC boards in the following
order:  control, voltage,logic,pro-
cedure,option,timer, remote inter-
face,speedmeter and voltmeter.
NOTE:  Some of the above PC
boards are optional and may not
be used in all NA-5 control units.
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							F-6TROUBLESHOOTING & REPAIRF-6
NA-5
Observe all Safety Guidelines detailed throughout this manual
If for any reason you do not understand the test procedures or are unabl\
e to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you p\
roceed. Call 216-383-2531 or 1-800-833-9353.
CAUTION
WIRE FEEDING PROBLEMS
PROBLEMS
(SYMPTOMS)POSSIBLE AREAS OF
MISADJUSTMENTS(S)RECOMMENDED
COURSE OF ACTION
The wire will not feed and the circuit
breaker (CB1) trips when the inch
down, inch up or the start buttons
are pressed.  The wire drive motor
does not turn.  
When the inch up button is press the
wire feeds down.  When the inch
down button is pressed the wire
feeds up.  1.  Check for a mechanical restric- tion in the wire feeding path.
2.  Make sure the proper input volt- age (115VAC) is applied to the
NA-5 control unit.
3.  Check the F102 field fuse on the power board.  Replace if faulty.
Note:  Frequent motor polarity
changes can cause the fuse to
fail.  This can be caused by the
following: •A welding procedure withfrequent electrode to puddle
shorting. 
•A power source output too low to establish an arc.
1.  The welding head is designed to feed wire in the proper direction
when it is installed as shipped
from the factory.  If the nozzle
and wire straightener aare rotated
about the axis of the gearbox
outpu shaft, the wire may feed in
the opposite direction.
Interchange leads #626 and #627
at the terminal strip (TS2) inside
the control box.  See wiring dia-
gram.1.  Perform the Wire Drive Motor
Test.
2.  The power board may be faulty. See Table F.1.
3.  Check the motor control cable for “shorts’ or “grounds”.
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							F-7TROUBLESHOOTING & REPAIRF-7
NA-5
Observe all Safety Guidelines detailed throughout this manual
If for any reason you do not understand the test procedures or are unabl\
e to perform the tests/repairs safely, contact the Lincoln Electric
Service Department for technical troubleshooting assistance before you p\
roceed. Call 216-383-2531 or 1-800-833-9353.
CAUTION
WIRE FEEDING PROBLEMS
PROBLEMS
(SYMPTOMS)POSSIBLE AREAS OF
MISADJUSTMENTS(S)RECOMMENDED
COURSE OF ACTION
The wire will not feed when the inch
down button is pressed.  The wire
does inch up OK and feeds down
when the start button is pressed.1.  If a DC400, Pulse Power 500 or a CV400 power source is used a
Diode Kit must be installed in the
power source.  
2.  Check to see if light 7J on the logic board is ON while the inch
down button is pressed.  If it does
NOT light check the inch down
button and associated leads.
See wiring diagram.  •(For codes below 8300)
If
light 7J DOES light when
the inch down button is
pressed the logic board
may be faulty.
•(For codes above 8300)
Jumper the AUTO tabs on
the voltage board and press
inch down button.  If the
wire does NOT feed down
the logic board may be
faulty.
1.  Disconnect the white #21 lead from the NA-5 polarity terminal
strip (TS1).  See wiring diagram.
With the inch down button
pressed read the ACTUAL volts
on the NA-5 digital voltmeter.
The digital meter should read
over 19 volts and the wire should
inch down.  If not, perform the
Voltage Board TransformerTest.
If the test is OK the voltage
board may be faulty.  Replace.
2.    If the voltage is over 19 volts and the wire DOES inch down
with the #21 lead disconnected
reconnect the #21 lead to the
terminal strip and read the
ACTUAL volts with the inch
down button pressed.  If the
voltage is less than 8 volts per-
form the 
#21 - #67 External
Resistance Test.   
If the resis-
tance test is OK the voltage
board may be faulty.  Replace.
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