Alesis QS7.1 Service Manual download pdf (Page 16)

Alesis QS Series Keyboards Service Manual V1.00 11/19/06

2.00 Theory Of Operation

2.10 Power Supplies

2.11 QS6/QSR Power Supply

The power supply begins with the Alesis P4 type transformer input at J1 J15. After the

power switch (SW2 S1), the signal is rectified (D1, D2 D12 D11), input filtered (C3, C9 and C25

C86, C80 and C81), regulated (U9, U10 U31, U32), and finally output filtered (C24, C32 and

C35, C34 C77, C78 and C82, C83) into the +5V and -5V supplies needed by the unit. In

addition, many 0.1µF capacitors are located throughout the system to act as supply filters. Note

that the +5V rail requires a lot more filtering due to the digital supply needs.

2.12 QS7/QS8 Power Supply

2.12A Transformer PCB

Input from R.F.I. filter enters the Transformer PCB via J1. The current is fused (F1)

prior to the primary of the ECO 4 Transformer (X1). Note that the transformers of countries

outside the United States are varied according to the power grid requirements for that country.

Output from the transformer PCB is routed to the main PCB via J2.

2.12B Main PCB

Transformer output is bridge rectified (D1, D2, D4 , and D5), input filtered (C8, C96, and

C15), regulated (U6, U4), and finally output filtered (C38, C34, C18, and C24) into the +5V and

-5V supplies needed by the unit. In addition, many 0.1µF capacitors are located throughout the

system to act as supply filters. Note that the +5V rail requires a lot more filtering due to the

digital supply needs.

2.13 SRAM Battery Backup

The user storage/system SRAM requires a small standby supply current while it is

normally powered down. The battery current is supplied via a transistor circuit (Q7 Q4 Q4)

designed prevent the +5V rail from trying to charge the battery, while ensuring that a solid +5V

is supplied to the SRAM during normal operation.

2.20 Analog Signal Paths

Since these units are largely digital in nature, analog signals are limited to two major

types:

☞ Audio Signal Output

☞ Slider and Aftertouch strain gauge input

2.21 Main Outputs

Differential analog output from the DAC is anti-alias filtered and buffered by U6A U3A

U3A (left) and U6B U3B U3B (Right). This signal is sent to the stereo output level slidepot R1

R2 via J11 J4 J1.

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Alesis QS7.1 Service Manual Page 16