Roland Boss DR-55 Service Manual free download

File name Boss DR-55 Service Manual.pdf

FEB. 21,1980 1 RS FLIP FLOP (2/4 IC3) (a) PLAY Mode When the START switch S5 is turned ON, the Q cutput goes to H and trig- gers the Clock Generator (2). Mhen the STOP switch S6 is turned ON, the Q output goes to L and the Clock Generator stops oscillation. At this time, the Q output goes to H and resets the Binary Counter (5) (b) WRITE Mode The Q output goes to H when S5 is turned ON, and goes to L when S6 is turned ON. This condition is written in the Memory IC1 as a data. 2 CLOCK GENERATOR (2/4 IC3) The frequency of this oscillator is controlled with TEMPO VR-5. This oscillator functions in PLAY mode only, and feeds clock pulses to the Counter (5) 3 SCHIMITT TRIGGER (Q15, 17, 18) This circuit functions in WRITE mode only. The collector of Ql5 goes H when either the START switch S5 or the STOP switch S6 is turned ON, and goes to L when the switch set to ON is turned OFF. 4 DELAY CIRCUIT (Q16) The output from the Schmitt circuit (3) is intergrated, and fed to the base of Q16. Then the signal is trimmed to square wave at collector of Ql6. This output signal is differentiated and becomes pulses, and then is applied to the R/~W terminal of IC1. The two pulses lag a little behind edges of Scmitt (3) output pulse. 5 DUAL BINARY COUNTER (IC2) This circuit counts pulses from the clock generator (2) in PLAY mode, and counts pulses from the Schmitt trigger (3) in WRITE mode, and then outputs binary-coded signals from the terminals Ql-Q5; Ql-Q4 denote 16 steps composing each rhythm. Signal from Q5 is applied to A7 only when the VARIATION switch is set to AB. To the terminal A7, the L level voltage is given when the switch is set to A and H when switch is set to B. DR-5 5 6 256 x 4 BIT CMOS MEMORY (IC1) Reading/writing from/to this memory is as described below. The upper 3 bits designate rhythms 1-8, the next one bit designates VARIATION A and B, and. the lower 4 bits 16 steps in one rhythm. In PLAY mode, the terminal CE2 is connected. to the Clock generator output. The memory functions only when the clock is H, and outputs H's or L's from DO 1-4. (When the clock is L, DO 1-4 becomes high impedance.) In WRITE mode, when the terminal R/~W becomes L,a data from the flip flop is written in one of DI 1-4 via Sl.A previously stored data is rewritten from DO via R61-R64 to the remaining three DI's. The Vcc of this rnemory chip is directly connected to the dry cells regardless of power switch positions, since the chip draws only a very slight idling current during stand-by. As a result, the data is guaranteed to be stored as long as the dry cells maintain voltage value higher than a specified. level. The capacitor C39 (22 mfd.) connected to the terminal Vcc can substi- tute for the dry cells by its charge for several minutes when the cells are absen