3-6
Although the Power Supply exhibits the least failures of all 4020 sub-
assemblies, many power supplies are being damaged by reversal of the battery
leads.
Note:
The 4020 battery harness includes a 15 amp fuse to prevent
overload and battery reversal damage.
D
O NOT
replace the 15 amp fuse with the 30 amp fuse used in
the 4100 system.
The higher 30 amp fuse damages the battery reversal protective
diode D17 located on the 565-235 Universal Switcher PCB
assembly within the power supply.
Many Power Supplies are heavily loaded at the time of installation or after
subsequent system upgrades. Simplex TRs have indicated that it has been
necessary to use power from both the A and B taps to supplement B-tap power
to system peripheral devices.
The 28 volt A-tap voltage is essential for panel sub-assembly operation. If the
A-tap power is lost, the panel shuts down. If you must use A-tap power, connect
internal panel devices or steady load devices such as LCD Annunciators to this
tap. All relays should be suppressed.
Note:
Under no circumstances use the C-tap. This tap is reserved for
the charger. Any additional load may cause over heating.
When a 4020 power supply Trouble indication occurs, the supply is typically the
first item replaced and often the supply is not, in fact, the cause of the Trouble.
Service Repair data indicates that 4020 Power Supply sub-assemblies only
exhibit an 11% failure rate. A damaged Standard Slave or Power I/O card can
also produce power supply Trouble indications.
Problems Associated with Power Supplies
Power Supply Damage due to
Battery Lead Reversal
Power Supply Loading
Power Supply Trouble
Indication
