Manual 0-2957 4-15 TROUBLESHOOTING
4.10 Test Procedures
The test procedures in this subsection are referenced in
the troubleshooting section.
A. Safety Precautions
1. Significant DC Voltage exists after removal of input
power. Allow two minutes for discharge time. Volt-
age measured on input capacitors must be zero be-
fore performing service on the power supply.
2. Do Not touch electrical components with any part of
the human body when power is applied.
3. Keep away from any moving parts.
4. Hot surfaces can cause severe burns. Allow equip-
ment to cool before servicing.
5. Electrostatic discharge can damage printed circuit
board assemblies. Transport printed circuit boards in
proper antistatic shielded packages. Use proper
grounding techniques with wrist strap before handling
printed circuit boards.
6. Misaligned plugs can cause printed circuit board dam-
age. Be sure plugs are properly aligned and com-
pletely seated.
7. Excessive pressure can damage printed circuit boards.
Use only minimal pressure and gentle movement
when disconnecting or connecting printed circuit
board plugs.
B. Diode Testing Basics
WARNING
Disconnect primary power at the source before dis-
assembling the power supply, torch, or torch leads.
Testing of diode modules requires a digital volt/ohm-
meter that has a diode test scale. Remember that even if
the diode module checks good, it may still be bad. If in
doubt, replace the diode module.
1. Locate the diode module to be tested.
2. Remove cables from mounting studs on diodes to iso-
late the module.
3. Set digital volt/ohmmeter to diode test scale.
4. Using the Figures for each test, check each diode in the
module. Each diode must be checked in forward bias
(plus to negative) and reverse bias (negative to plus)
direction.
5. Connect the volt/ohmmeter positive lead to the an-
ode (+) of the diode and the negative lead to the
cathode (-) of the diode for forward bias testing (re-
fer to following figure). A properly functioning di-
ode will conduct in the forward bias direction and
indicate between 0.3 to 0.9 volts.
0.75
VR
COM
A
Art # 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”.
OL
VR
COM
A
Art # A-00306
Anode
Cathode
Reverse Bias
Diode Not Conducting
+
_
Testing Diode Reverse Bias
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