Commodore 1540/1541 Service Manual: Power Up/Down Write Protection

1541 CIRCUIT THEORY

Power Up/Down Write Protection

This circuit prevents erroneous data from being written on the disk during power up/down sequences. During a power up, the 12VDC supply is not applied to the R/W coils and amplifier circuits before the processor has control of the logic. During a power down the 12VDC supply is removed from the R/w coils and amplifier circuits before the processor loses control of the logic.

Q1 acts as a series pass transistor, biased to regulate the 12VF output to the R/W coils and Amplifier circuits. Q2 is a feedback amplifier monitoring the 5VDC supply. CR5 develops a precise reference voltage for Q2. L8 and C15 delay the 12VDC supply.

This page has been created by Sami Rautiainen.
Last updated April 18, 1998.
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