Power Supply; Battery Backup - Alesis D4 Service Manual

2.00 Power Supply

The power supply begins with the 9V A.C. 750 mA transformer (Alesis P3 type). After being R.F.
filtered by C26, and passing through the power switch, the A.C. is rectified into -12V, and +12V by D1
{D10}, D2 {D11}, and C2/C3 {C111/C112}, C1 {C108}. Regulators supply the +5V and -5V needed to
run the unit. Note that the +12V raw supply (From D2) {D11} is used by the system reset circuit (see
section 3.11) and battery backup (section 2.10). The D4's +12V and - 12V lines are also used to power
the output op-amps via the PUP Circuit (section 2.20). +5V and -5V lines are used to power the PUP
circuit in the D5.

2.10 Battery Backup

The battery backup circuit is more complex than it first appears, as it requires a good system
reset (see section 3.11) to function properly. The actual backup circuit consists of the 3V battery, a
current testing resistor (R38) {R92}, a steering diode (D6) {D2}, a Diode/Transistor/Resistor
combination (D7, Q3, R24) {D1, Q6, R85} that acts as a steering diode, and filter capacitor C33 {C27}.
The D/T/R combination serves a duel purpose. Besides acting as a steering diode, it also ensures that
the supply voltage level of the SRAM is higher than the level of the data buss. This prevents data
corruption during normal operation.
Alesis D4/D5 Drum Modules Service Manual
Diagram 2
2 02/19/03