Miller Electric S-21E, Technical Manual

Page: 21 / 48

8-4. MOTOR BOARD
PCi TESTING INFORMA-
TION (Figure 8-1 And Diagram 8-2)
A
W
ARNING: ELECTRIC SHOCK can kill.
Do not touch live electrical parts.
• Shut down wire feeder and welding power
source or stop engine before making or
changing meter lead connections and before
disconnecting or connecting any leads.
MOVING PARTS can cause serious injury.
• Keep away from moving parts.
HOT SURFACES can cause severe burns.
• Allow cooling period before servicing.
This procedure requires the unit to be ener-
~ized. Only qualified persons familiar with and
ollowing standard safety practices are to per-
form this testing procedure.
A
CAUTION: ELECTROSTATIC DISCHARGE
(ESD) can damage circuit boards.
• Put on properly grounded wrist strap BE-
FORE handling circuit boards.
• Transport circuit boards in proper static-
shielding carriers or packages.
• Perform work only at a static-safe work area.
INCORRECT INSTALLATION or misaligned
plugs can damage circuit board.
• Be sure that plugs are properly installed and
aligned.
EXCESSIVE PRESSURE can break circuit
board.
• Use only minimalpressure and gentle move-
ment when disconnecting or connecting
boardplugs and removing orinstallingboard.
IMPORTANT:
For all checks, be sure to test and verify
the continuity of leads between the board and the area
where check is performed. All checks shouldgo through
the connections and be actual terminal-to-terminal tests
so that bad connections or leads and corrosion are not
the problem.
A. Preliminary Checks
1. Check that jumper plug PLGl is secure in recep-
tacle RC1 on Motor Control Board PCl.
2. Check that plug PLG2 is secure in receptacle
RC2 on Motor Control Board PCl.
3. Check that plug PLG3 is secure
in
receptacle
RC3 on Motor Control Board PCl.
4. Check that plug PLG4 is secure in receptacle
RC3 on Motor Control Board PCi.
B. Power Supply Circuit
Input power of 24 volts ac should be present between
pins A and B of receptacle RC4. If 24 volts ac are not
present, check POWER switch 51 and circuit breaker
CBl for proper operation with an ohmmeter.
An output voltage of +24 volts dc should be present at
pin A of receptacle RC2 with respect to circuit common.
If +24 volts dc are not present at pin A, replace Motor
Control Board PCl.
An output voltage of +6.5 volts dc should be present at
pin C of receptacle RC2 with respect to circuit common
with gun trigger pressed. If +6.5 volts dc are not present
at pin C, replace Motor Control Board PCi.
C. Trigger Circuit
When the gun trigger is pressed, +19 volts dc should be
present at pin B of receptacle RC2 with respect to circuit
common otherwise the voltage at pin B should be 0 volts
dc when the gun trigger is not pressed. The trigger signal
is then supplied to pin A of receptacle RCl as a motor
start/stop control signal and also supplied to pin B of re-
ceptacle RCl to control gas valve GS1 and contactor
control relay CR1 on PCi.
D. Wire Feed Speed Circuit
The 0 to +6.5 volts dc wire feed speed command input
signal should be present at pin D of receptacle RC2. The
wire feed speed command signal is compared to the
current and voltage feedback from Motor Ml thereby
providing the proper voltage output of 0 to +24 volts dc
to wire drive motor Ml through pins D (positive) and C
(negative) of receptacle RC4. If 0 to +24 volts dc is not
present between pins C and D of RC4, replace Motor
Control Board PCi.
5-2iE TM-i 57i Page 17