Precision Control Systems 3629C - Manual (Page 25)

MODEL 3629C 21 04/10/2007
TROUBLESHOOTING (Continued)
SYMPTOMS POSSIBLE CAUSES
LOAD POWER AT MAXIMUM.
'COMMAND' LED IS ON OR OFF.
SHORTED SCR.
Check for illuminated "SHORTED SCR" LED.
PROBLEM ON THE CIRCUIT BOARD.
Remove or swap circuit board to determine if the problem
exists on the circuit board.
LOAD POWER AT MAXIMUM.
'COMMAND' LED IS ON
PROBLEM WITH THE COMMAND SIGNAL.
Remove the command connector. If load power and
line current indicators go off, the problem is
associated with the command signal.
PROBLEM ON CIRCUIT BOARD.
If, after removing the command connector, the command
indicator remains on, the problem is probably associated
with the circuit board.
LOAD VOLTAGE WILL NOT
REACH MAXIMUM.
INSUFFICIENT COMMAND SIGNAL.
Determine that the command signal is at maximum.
INSUFFICIENT LINE VOLTAGE.
Measure the voltage from phase to phase on the line
and load terminals. If the voltage is correct at the load
terminals but not at the load, check load wiring or external
load fuses.
CURRENT LIMITING IS ACTIVE.
Current limit LED is on. The current limit prevents
excessive current when controlling variable resistance
loads. It is recommended that the current limit not be
changed until the load requirements and the controller
ratings are thoroughly understood.
INCORRECT SPAN ADJUSTMENT.
If the span adjustment pot is adjusted incorrectly, the
controller may be unable to reach maximum output.
INCORRECT LOAD WIRING.
On new installations, check the load connections carefully.
FAULTY SCR OR CONTROL CIRCUIT.
With a digital voltmeter set on the 2000 Vdc range, check
for a DC voltage present on the load output terminals of
the controller. More than 1Vdc between any of the three
load outputs could be due to a faulty SCR or control
circuit. If the line current indicators are on, the circuit may
have failed. If one LED is bright and the others are dim, an
SCR or its connections may have failed.
Follow this procedure to determine which SCR is shorted.
1. Remove power from controller.
2. Disconnect all Line and load leads from the controller.
3. Measure the resistance between line 1 and load 1 terminals, then between line 2 and load 2 terminals and
between line 3 and load 3 terminals.
If any measurement is less than 1000 ohms, one or more SCR(s) have failed.