Thermal Arc 6045 EXCEL-ARC, Руководство по эксплуатации

Страница: 41 / 76

EXCEL-ARC 500, 6045
August 22, 2005 5-5
2. SCR Malfunction:
A failed or defective SCR will normally result in one of
two situations.
1. SCR shorted: Normally results in blown line fuse and
shorted output on the machine. To isolate which SCR
has failed it will be necessary to disconnect the
transformer leads from the SCR heatsinks and check
each SCR individually with a VOM.
2. SCR open: Normally results in a reduction in output
voltage and/or an erratic or unstable arc. The same
effect will be caused by the lack of a gate drive signal
to an SCR. Check all gate leads from the control board
and suppressor board to the SCRs. The following table
gives typical values for open circuit voltage with one
or more SCRs not firing.
NOTE
For CV machines disconnect cable #103 from
the capacitor bank assembly and insulate the
lug to prevent it from touching chassis, prior
to measuring open circuit voltage. These
values were recorded at nominal line voltage
with voltage/current control set to maximum.
CC Mode CV Mode
All SCRs firing 61 VDC 48 VDC
1 SCR not firing 55 VDC 46 VDC
2 SCR not firing 48 VDC 43 VDC
3 SCR not firing 41 VDC 39 VDC
Table 5-3: SCRs
The best way to isolate the particular SCR which is
malfunctioning is as follows. Refer to Connection Diagram
while inspecting the unit. On the output rectifier there are
gate leads coming off of the SCRs. Each of these leads
are connected to a quick-disconnect terminal on the
suppressor board. Turn the voltage control pot to
maximum. Disconnect one lead to one SCR and observe
the OCV. If the OCV drops to a lower value, this indicates
that this particular SCR is working properly.
Reconnect
this lead and do the same thing with the remaining leads
until you discover which disconnection does
not cause
the OCV to drop to a lower level. This is the malfunctioning
SCR. See Mounting Procedures for SCRs which follows.
3. Mounting Procedure for SCRs:
1. Thoroughly clean heat sink surface to eliminate any
dirt or contamination.
2. Apply a thin coat of Alcoa #2 compound to cleaned
surface. Alcoa #2 is available from Thermal Arc, part
number 903870.
3. Positively locate the SCR in place in the heat sink. A
small spring pin in the extruded heat sink will locate
the SCR.
4. Place the clamp in position with the bolts through the
holes in the heat sink, and proceed in following
manner.
5. Tighten the nuts evenly until finger tight.
6. Tighten each bolt in 1/4 turn increments using correct
size hex key.
7. Place the Force Indicator Gauge (903878) firmly
against the springs as shown. Be sure both ends and
the center are in firm contact with the springs. The
gauge notch location will indicate the spring deflection
or force. Correct mounting force is indicated as shown
below.
8. Spring deflection over 2-1/4 inches of spring is .037"}
.002" for all clamps.
9. All clamps to be set at 4° mark. This corresponds to
the VE3000-VE2500 section on the gauge label.
Art # A-06065
Force Gage, shown in
position (903878)
Clamp (405140)
Heat Sink
Heat Sink
Figure 5-1: SCR with Force Gauge Shown in Position