Thermal Dynamics (a Thermadyne Company) Merlin 3000 - Manual (Page 24)

SERVICE TROUBLESHOOTING 20 Manual 0-2533
E. Fuse blown at disconnect when primary power is
connected
1. Voltage selection busbars connected incorrectly
a. Check and correct if necessary.
2. One leg of three-phase primary connected to chassis
ground
a. Rewire input cable per Operating Manual.
3. Main transformer shorted
a. Replace main transformer
F. Fuse blown at disconnect when main contactor
(W1 or W2) closes
1. Shorted input diode (D1-D6)
a. Refer to Section 4.05-E, Diode Check. Replace
diode(s) as required.
2. Switching transistor (Q1) shorted to heatsink
a. Replace Q1, check heat-sink for possible dam-
age. Refer to Section 4.05-M, Switching Con-
trol Check (Q1).
3. Shorted input capacitor (C7-C12)
a. Replace capacitor if necessary
4. Shorted diode (D11-D14)
a. Check for proper 3-phase power at input termi-
nal board, check diodes. Refer to Section 4.05-
E, Diode Check.
5. Faulty Voltage Selection PC Board
a. If W1 and W2 come on simultaneously replace
Voltage Selection PC Board.
6. Faulty main contactor (W1 or W2)
a. Check both contactors for welded contacts and
replace contactor(s) if necessary
G. TEMP indicator on (red)
1. Unit overheated
a. Clean radiator and check for obstruction.
b. Excessive piloting; allow unit to cool
2. Faulty thermal sensor (TS1, TS2, or TS3)
a. Refer to Section 4.05-F, Thermal Sensing Circuit
Circuit Check. Replace sensor(s) if necessary
3. Faulty Logic PC Board
a. Refer to Section 4.05-F, Thermal Sensing Circuit
Check. Replace Logic PC Board if necessary
4. Faulty LED/Current Control PC Board
a. Refer to Section 4.05-F, Thermal Sensing Circuit
Check. Replace LED/Current Control PC
Board if necessary.
H. No GAS indicator; Motor and Pump operating;
Other LED indicators normal; Both gases flow
1. Front panel RUN/SET/PURGE switch set to PURGE,
or PURGE selected at Remote Control
a. Normal operation (purges plasma line only, sec-
ondary pressure switch is not satisfied)
2. Gas pressure set too low
a. Adjust pressure
3. Faulty pressure switch (PS1 or PS2)
a. Jump switches one at a time and check for indi-
cator to determine which has failed. Replace
switch if necessary.
4. Faulty Logic PC Board
a. Refer to Section 4.05-G, Pressure Sensing Cir-
cuit. Replace Logic PC Board if necessary
5. Faulty LED/Current Control PC Board
a. Refer to Section 4.05-G, Pressure Sensing Cir-
cuit. Replace LED/Current Control PC Board
if necessary.
6. Faulty SW3-B (secondary mode set to O2 or H2O )
a. With secondary mode set to O2 or H2O, check
for continuity from wire #52 to #55 on SW3-B.
If open, replace SW3-B.
7. If using Gas Control Option (GC3000) set for Water
Secondary, faulty SW2-C in Gas Control.
a. With Merlin front panel secondary mode set to
GAS and the Gas Control (GC3000) set to
WATER, there should be continuity from wires
#52 to #55. If not, SW2-C or connections to it
are faulty.
I. GAS indicator off, plasma and/or secondary gas
does not flow
1. Front panel RUN/SET/PURGE switch set to PURGE,
or PURGE selected at Remote Control.
a. Normal operation (purges plasma line only, sec-
ondary does not flow)
2. Secondary mode set to O2
a. No secondary flow is normal operation in O2
mode (but GAS indicator should be ON). Re-
fer to symptom 'H' above.