Commodore 1540/1541 Service Manual: Read Amplifier Circuits

1541 CIRCUIT THEORY

Read Amplifier Circuits

When data is recorded on the disk, a "1" bit is represented on the disk by a change in direction of magnetic flux, caused by a change in direction of current passed through the R/W coil in the R/W head. When a "0" bit is to be recorded, no change in current flow direction occurs, causing the direction of the magnetic flux to remain the same on the disk.

When data is being read from the disk, CEMF is induced into the R/W coil by the magnetic fields on the disk, causing current flow which is detected by the read amplifiers. Current flow through the R/W coil will forward bias wither CR16 or CR17, depending on the direction. Q7 and CR14 must be forward biased. The first amplifier UF3, senses this current flow from the R/W coil on one of the inputs and amplifies it. L9, L10, L11, L12 and C45 act as a low pass filter, suppressing noise on the amplified output. UF4 is a differential amplifier which amplifies the difference of the two input signals from the filter section. UE4 is a peak detector. The output of UE4 will pulse "high" when a "1" is read. This signal is then reconstruction of the data recorded. The Time Domain Filter, UD4, times out when a "1" bit has been read, so unwanted "1" bits are not added to the actual data. The One Shot UD4 generates the correct data pulse width so the PLA can convert the data to parallel for processor control.

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