Power Slupply And Power Supply Protective Circuits - Radio Shack TRS-80 PT-210 Service Manual

Power Supply and Power Supply Protective Circuits
*
Power supply
The standards of DC voltages are as follows.
+5V is-supplied to pCPU, the digital circuits, the modem, and the RS-232C interface. 4-5.0
-
6.1V is
supplied to the thermal head,+7.5Vis supplied to motors and solenoids, and k 1 2 V is supplied to the
analog circuit elements of the modem.
*
Power supply protective circuits
A protective function is actuated when abnormal current flows at the time of power ON or when the
PT-210 Portable Data Terminal operates.
Item
I
Protective function
5 short
1
protection by IC3 on the power supply board.
AC line primary
side short
1
Protection by NFB (No Fuse Breaker).
Â
1 2V short
+
7.5V and
4-
5.0-6.1 V short
Caution: Immediately turn the power switch to the OFF position if the specified DC voltage is not pro-
duced.
Check fuse 1, fuse 2, and the NFB for blowing before turning the power switch back to the
ON position after repair and recovery. If any of them is blown, replace it with a spare.
protection by ICI, IC2 on the power supply board.
Protection by fuse 1 or furse 2 or by the
circuit breaker on the power supply board.