Thermadyne CE CutMaster 75, Service Manual

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Manual 0-2869 4-11 SERVICE TROUBLESHOOTING
0.75
VR COM A
A-00307
Anode
Cathode
Forward Bias
Diode Conducting
+
_
Diode Test Symbol
Testing Diode Forward Bias
6. Reverse the meter leads across the diode for reverse
bias testing (refer to following figure). A properly
functioning diode will block in the reverse bias di-
rection and depending on the meter function will
indicate an open or “OL”.
7. If a diode checks bad, replace the diode module.
8. Reconnect all cables.
OL
VR COM A
A-00306
Anode
Cathode
Reverse Bias
Diode Not Conducting
+
_
Testing Diode Reverse Bias
C. Diode Module Board Tests
WARNING
Disconnect primary power at the source before tak-
ing any resistance checks.
1. Input Diode Module Board Circuit Test
a. Remove AC power. Refer to Appendix 5-A or 5-B,
Main Power Wiring diagram.
b. Check Input Diode for shorted input diode. With
an ohmmeter set on the diode range make the fol-
lowing checks from Main PC Board to Input Di-
ode:
For 400-Volt, 460-Volt, and 600-V Power Supplies:
Meter + Meter - Indication
E15 E1 Diode Drop
E1 E15 Open
E15 E2 Diode Drop
E2 E15 Open
E15 E3 Diode Drop
E3 E15 Open
E7 E1 Open
E1 E7 Diode Drop
E7 E2 Open
E2 E7 Diode Drop
E7 E3 Open
E3 E7 Diode Drop
E7 E15 Open
E15 E7 Diode Drop *
400-V and 460-V Input Diode PCB
* Indication can be twice
other indications.
For 208/230V Power Supplies:
Meter (+) Meter (-) Indication
E7 E1 Open
E1 E7 Diode Drop
E15 E1 Diode Drop
E1 E15 Open
E15 E7 Diode Drop *
E7 E15 Open
208/230V Input Diode PCB
* Indication can be twice
other indications.