5: Maintenance
5-8 PRC-BC4-MS
3. If the fault only occurs when using an external DC power source,
check all internal and external wiring and connections.
4. Check rectifier bridge BR1 by measuring the resistance across each of
the four internal diodes. If the forward resistance is less than 10 ohms
and the reverse resistance in very high (mega ohms), the diode is okay;
if it is not, replace the diode.
5. On rectifier bridge BR1, measure the resistance from the (+) terminal
to the (–) terminal. If the resistance shows a short, lift all the
connections to the bridge and remeasure. If the measurement still
shows a short, replace the rectifier bridge. If there is no short, skip to
step 8.
6. Remove DC fuse F2. If the resistance measurement in step 5 still
shows a short, check each of the power supply filter capacitors for
short circuits. Replace any capacitors that are shorted and remeasure
across the bridge terminals.
7. If the resistance measurement in step 6 still shows a short with the DC
fuse removed, the short is on the inboard side of the fuse. The short
can be isolated by lifting the various connectors or pressing each
RESET button one at a time.
8. Measure the resistance of the power transformer windings. The
resistance should be a very low resistance (typically less than
10 ohms.
Status LEDs This section assumes the status LEDs are either not lighting or lighting at the
wrong time.
1. Turn the PRC-BC4 on. If more than one LED lights up at one time,
turn the PRC-BC4 off and measure the resistance across each diode on
the Display board.
2. If the FAULT LED lights up properly, skip to step 5.
FAULT LED Failure:
1. If the FAULT LED is not lighting up correctly, measure the voltage at
charger IC pin 11. The measured voltage should be at least 10 VDC
during a fault (battery is under 4 VDC) condition; if it is not, replace
the charger IC.
2. If the voltage measured in step 1 is okay but the
FAULT LED does not
light up, check the LED and the series resistor wiring.
3. Measure the voltage on the op amp non-inverting input pin. It should
be 1.2 to 1.5 VDC; if it is not, turn the PRC-BC4 off and measure the
resistance to determine if it is shorted to ground. If there is no short,
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