2.High frequency protection for the input rectifier diodes (D1-6) is provided by capacitors C1 - C6 and MOV 1-3, which are located between each side of the diode heatsink on the input filter PC board. Except for the shorts, these components can not be checked with a volt/ohm meter. To be safe, the complete input filter board should be replaced any time an input diode fails.
3.Diodes can overheat if air flow over the heatsink is not adequate or if the diode is not properly fas- tened to the heatsink. Check that all small diodes (D7-14) are torqued to 20-25 in-lbs (2.3-2.8 Nm) and all large diodes (D1-6) are torqued to 34 in-lbs (3.8 Nm). Apply a light film of electrically con- ductive heatsink compound between the diode and heatsink. Make sure air passages in and out of the unit are not obstructed.
4.Diodes that are faulty at the time of manufacture are difficult to diagnose. These diodes generally fail within the first few hours of operation. Before deciding that this was the case, be sure to check out other possibilities.
F.Thermal Sensing Circuit Check
1.Thermal sensors TS1, TS2, TS3, TS4, and TS5 are connected in series to J1-9 on the Logic PC Board. TS2 is a PTC resistor whose resistance varies with temperature from about 100 ohms at room tem- perature (68°F/20°C) to 3.3K at 140°F (60°C) switch point. TS1, TS3, TS4 and TS5 are switches nor- mally closed, 0 ohms, that open at over tempera- ture. TS1, TS4 and TS5 are part of the Main Trans- former Assembly. TS2 is on the Heatsink and TS3 is on the Pilot Resistor.
Check the voltage from J1-9 to test point TP1 (or J1-8) on the Logic PC Board for less than 7.5 VDC.
If the voltage is greater than 7.5 VDC, the unit is overheated or a temperature sensor is faulty.
2.If the unit still operates but the TEMP indicator is red, the problem may be on the LED PC board. If the voltage is less than 7.5 VDC, check the voltage from J3-4 to test point TP1 (ground). If the voltage is greater than +4 VDC (and the TEMP indicator is lit red), replace the LED PC board. If the volt- age at J3-4 is less than 4V, replace the Logic PC Board.
G.Pressure Sensing Circuit
Pressure switches PS1 and PS2 are connected in se- ries to J1-7 on the Logic PC Board. PS2 is jumpered out by SW3-B when the unit is set to the O2 (no sec- ondary gas) or water secondary mode or by SW2-B in the GC3000 Gas Control if that option is installed.
1.Check the voltage at J1-7 for less than 1 VDC with gases flowing and operating pressure greater than 35 psi (2.4 BAR).
2.If the voltage at J1-7 is less than 1 VDC, check the voltage at J3-3. If the voltage at J3-3 is greater than 12 VDC, replace the Logic PC Board. If the volt- age at J3-3 is less than 12 VDC, replace the LED PC Board.
H.Gas Solenoid Circuits
1.Set the RUN/SET/PURGE switch to SET position. Measure continuity between the center terminal of the switch (wire #62) and each outer terminal (wires #61 and 63). If the resistance is less than 1000 ohms, replace the RUN/SET/PURGE switch.
2.If the resistance is greater than 1000 ohms, apply power and check for 120 VAC between wire #110 and J2-3 for plasma and J2-7 for secondary. If 120 VAC is present at one point and not the other, re- place the Logic PC Board.
3.If no voltage is present at J2-3 or at J2-7, check for 120 VAC at J2-5 (the Logic PC Board input). If 120 VAC is present at J2-5, replace the Logic PC Board. If not, check the 120 VAC voltage supply (refer to Section 4.05-A, Voltage Selection PC Board Check).
I.Coolant Flow Sensor Circuit Check
The flow sensor (FS1) for the coolant is calibrated for
0.25gpm (1.1 lpm). When adequate coolant flow sat- isfies FS1 it closes, connecting J1-5 on the Logic PC Board to J1-4 (common).
Measure voltage between J1-5 and J1-4 or TP1. If J1-5 is greater than 1 volt, FS1 or connections to FS1 are faulty. If J1-5 measures close to 0 VDC, check J3-2. If J3-2 measures less than +12 VDC, and the coolant flow indicator is not lit, replace the LED PC board. If J3-2 measures greater than +12 VDC, replace the Logic PC Board.
J.Coolant Conductivity Circuit
The conductivity probe consists of two insulated pins that extend into the coolant reservoir. The Logic PC Board sends out an AC voltage level on J2-24 that varies with the conductivity of the coolant.
1.Disconnect one of the wires to the conductivity probe (wire #57 or 58). The Logic PC Board will see infinite resistance and the coolant conductiv- ity LED indicator should be lit. If the coolant con- ductivity indicator is lit, replace the coolant. If the problem remains after coolant is changed, replace the conductivity probe.
