Thermal Arc ULTIMA 150, Руководство по обслуживанию

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SECTION 3: SERVICE TROUBLESHOOTING 24 Manual 0-2503
B. FET and Capacitor Assembly
The FET/Capacitor Assemblies can be checked by use of
an ohmmeter set to a diode scale.
1. Disconnect power from the unit.
2. Read the following on each of the two FET/Ca-
pacitor Assemblies:
• Diode drop from E2A to E3.
• Diode drop from E4 to E1A.
• Short from E3 to E4.
CAP
CAP
CAP
CAP
E2A
E2C
E1C
E1A
E2B
E1B
A-01102
(+)
( )
Figure 3-9 Capacitor PC Board Assembly Layout
3. With the meter on a low ohms scale, read the re-
sistance from gate to emitter on each of the FETs
(8 total on each assembly). These are the 3 leaded
devices along each edge of the assembly. Each
should read approximately 2.5K ohms from gate
to emitter (across the 2 outside pins of each de-
vice).
If any of these measurements are not correct, re-
place the affected FET and Capacitor Assembly.
Capacitors
Heatsinks
FET
FET
A-00837
Figure 3-10 FET Locations
C. Output PC Board/Diode Bridge Assembly
NOTE
The Ultima-150 has been manufactured using one
of two (2) models of Diode Bridge Assemblies - ei-
ther Model "A" or Model "B". Follow procedures
as they apply to your unit. All units with Unit
Serial Number ending with a letter prior to "G"
are made with Model "A". All replacement Diode
Bridge Assemblies are Model "B".
Make the following measurements with the power dis-
connected and with an ohmmeter set for a diode scale.
1. Measure a diode drop from each of the anode con-
nections of the diode to the cathode connection.
2. Measure a diode drop from negative output (E1
on the Pilot PC Board) to work lead.
If these measurements are not correct, replace the
Output PC Board/Diode Assembly.
A-01104
1 2 3
3 2
1
Figure 3-11 Model "A" Output Diode Bridge
A-01105
2
1
Figure 3-12 Model "B" Output Diode Bridge