2031 LP CIRCUIT THEORY

The Power Supply

The input AC voltage is controlled by switch 1 (SW1). Disk circuit protection is provided by fuse 1 (F1). If SW1 is closed, the AC voltage input is applied to the primary winding of transformer one (T1 T1 steps down the AC input voltage into two smaller AC voltages. The top secondary AC output (approx. 16VRMS) is converted to DC by the Full Wave Bridge Rectifier CR1. The DC output of CR1 is regulated at 12VDC by VR1. The bottom secondary AC output of T1 (approx. 9VRMS) is converted to DC by the Full Wave Bridge Rectifier CR3. The DC output of CR3 is regulated at + 5VDC by VR2. High frequency filtering is provided by C1 and C3 for the 12VDC supply, and C4, C60, C6-8, 10, 19-22, 31 etc. for the 5VDC supply. Low frequency filtering is provided by C51 and C2 for the 12VDC supply, and C52 and C5 for the 5VDC supply.

Reset Logic

The 2031 disk drive is automatically reset on power up by UF1, a 555 timer, when triggered by the 5V applied at pin 8. A reset can also be set by the IFC line on the IEEE Interface. The output pulse width is determined by the values of R43 and C36. The pulse width = 1. 1 x R43 x C36 = .5 seconds. The output on pin 3 of UF1 is an active "high". It is inverted by UC1 to active "low". A low output at UC1 pin 10 resets the unit and initializes all the microprocessor logic.