Lincoln TCV400, Operator'S Manual, Page: 25 / 31

E-6
TROUBLESHOOTING
E-6
TCV400
POWER RECTIFIER BRIDGE ASSEMBLY
CHECKING PROCEDURE
1. Bridge and Device Isolation
Disconnect the following, shown in Figure E.1:
a. Unplug P3 (G1, G2, G3, and 204) from the Control
PC Board.
b. Unplug P5 from the Snubber PC Board.
c. Secondary leads X1, X2, and X3 from the anodes
of the SCRʼs and cathodes of the diodes.
d. Disconnect positive bridge lead from shunt and
positive capacitor bank lead and from lug with dual
204 leads.
e. Perform following steps 2 and 3. If diodes and
SCRʼs are not shorted, bridge test is completed. If
any device appears shorted, disconnect the cath-
ode lead of each diode (4 total) and repeat steps 2
and 3.
ELECTRIC SHOCK
can kill.
• Have an electrician install and service
this equipment.
• Turn the input power off at the fuse
box before working on equipment.
• Do not touch electrically hot parts.
---------------------------------------------------------------------
WARNING
2. Power Diode Test
a. Establish the polarity of the ohmmeter leads and
set to X10 scale.
b. Connect the ohmmeter positive lead to anode and
negative lead to the cathode.
c. Reverse the leads of the ohmmeter from Step b.
d. A shorted diode will indicate zero or an equally low
resistance in both directions. An open diode will
have an infinite or high resistance in both direc-
tions and a good diode will have a low resistance
in Step b. and a much higher resistance in Step c.
3. Power Silicon Controlled Rectifier Test
The SCR must be mounted in the heat sink when
making this test.
a. Connect the ohmmeter (set to the X10 scale) leads
to the anode and cathode.
b. Reverse the leads of the ohmmeter from Step a.
c. A shorted SCR will indicate zero or an equally low
resistance in one or both directions.
d. Establish the polarity of the ohmmeter. Connect
the positive lead to the gate and the negative lead
to the cathode.
e. An open gate circuit will have an infinite or high
resistance. A good gate circuit will read a low
resistance, but not zero ohms. If gate circuit reads
zero ohms, check gate harness for shorts between
gate leads and 204 before replacing SCR.
FIGURE E.1
PLUG TO SNUBBER BOARD
SHUNT
P5
221 222
223
204
220
204
204
204
220
D1 D2 D3
SCR1 SCR2 SCR3
G1 G2 G3
D4
ANODE
CATHODE
ANODE
CATHODE
P3
Gate leads
plug to Control
P.C. board
To T1 main
transformer
To plug
P1
To (+) side
of capacitor
bank
_
+
X
1
X
2
X
3
GATE
_
+