SECTION 5
TROUBLESHOOTING
19
C. Power Boards, PB1/PB2, Troubleshooting (See
Figures 5-1 and 5-2)
Make sure input power is disconnected (OFF) and
voltage between T1 and T2 is zero.
Resistance Checks
(+)Probe
(-)Probe
Measurement
Drain-1
Source-1
5k ohms nominal*
Source-1
Drain-1
diode forward drop**
Gate-1
Source-1
1k ohms nominal*
Drain-2
Source-2
5k ohms nominal*
Source-2
Drain-2
diode forward drop**
Gate-2
Source-2
1k ohms nominal*
* Using meter high impedance diode scale.
** Using meter low impedance diode scale.
Voltage Checks (T.S. deenergized)
(+) Probe
(-) Probe
Measurement
TB-1(+)
TB-3(-)
324 V dc
TB-2(+)
TB-4(-)
325 V dc
Gate-1
Source-1
-12 V dc
Gate-2
Source-2
-12 V dc
P1-1
P1-3
24 V ac
P1-1
P1-2
12 V ac
P1-2
P1-3
12 V ac
P1-8
P1-10
24 V ac
P1-8
P1-9
12 V ac
P1-9
P1-10
12 V ac
D. Input Bridge, IBR, Troubleshooting
(See Figure 5-1)
Resistance Checks
(+) Probe
(-) Probe
Measurement
IBR-1,2,3
IBR (+)
diode forward drop**
IBR (+)
IBR-1,2,3
open*
IBR (-)
IBR-1,2,3
diode forward drop**
IBR-1,2,3
IBR (-)
open *
Voltage Checks
*Using meter high impedance diode scale.
**Using meter low impedance diode scale.
TB-1(+)
375-290 V dc @ 230 V ac
(+15%/-10%)
TB-4(-)
750-580 V dc @ 460 V ac
(+15%/-10%)
E. Output Bridge, OBR, Troubleshooting
(See Figure 5-2
)
Resistance Checks
(+) Probe
(-) Probe
Measurement
Anode-1
Cathode
diode forward drop**
Anode-2
Cathode
diode forward drop**
Cathode
Anode-1
open*
Cathode
Anode-2
open*
*Using meter high impedance diode scale.
**Using meter low impedance diode scale.
NOTE
If any of the above readings are incorrect, remove the
busbars and check modules OBR1-4 individually. Re-
place modules which are defective.
