And -12V Regulators; Power Supply, Unregulated - Centronics 101AL Technical Manual

Overvoltage protection is provided by components CR23, R41 and Q1. With
the output at a normal +5V, Zener diode CR23 inhibits current flow through
R41, holding the gate of SCR Ql at ground. However, when the output voltage
exceeds +6.8V, the Zener diode CR23 conducts, developing voltage across R4l
and turning on SCR Ql. This shorts the input and blows fuse F1.
To simplify troubleshooting procedures for the +5V regulator (as
well as the 12V supplies) the load may be removed from this supply by un-
plugging J2.
4.9.2 +12V and -12V REGULATORS (Figure 4-17)
The voltage generated by the 35 VAC center-tapped secondary winding
of Tl is used as inputs to the +12V and -12V regulators. The operation of
both circuits is identical to that of the +5V regulator described in Section
4.9.1.
As in the +5V regulator, the load may be removed from these supplies
simply by unplugging the J2 connector.
In addition, a jumper connection allows either the +12V output (E24
to E25) or +5V output (E25 to E26) to be connected to the character generators,
depending on whether a +12V or +5V ROM is used.
4.9.3 +35V POWER SUPPLY, UNREGULATED (Schematic #63015120 - Section 7)
The 27.5 VAC output from the transformer is rectified by diode bridge
MD1 and filtered by R1-C2 to generate the +35V unregulated voltage for the
power driver circuits. All of these components are located in the cavity.
This +35V output is fused through F4 and used as a voltage input to the power
driver board.
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