Pup Circuit; Digital Signal Paths; The 8031; Reset - Alesis D4 Service Manual

As mentioned before, the reset circuit is extremely important to battery backup. While covered
more extensively in later sections, it should be noted here that it ties into backup system at the SRAM's
chip enable line (pin 20) via Q4, and ensures that all access to the SRAM is shut off during power up,
and power down. In the case of the D5, reset is tied in through the D56IFT ASIC and Q5.
Any time any part of the backup circuit (including the SRAM) is changed, battery current should
be checked. This is accomplished by measuring the voltage across R38 {R92}. Specification for this is
R76
1mV<V <8mV. Most units are in the range of 1mV to 2mV. Values outside of the normal range
usually indicate a problem, and should be troubleshot.

2.20 PUP Circuit

The PUP (quiet Power UP) circuit is designed to prevent the unit from making noise during
power up. The circuit utilizes the RESET line (section 3.11) to control the power supply lines to U42
{U2}, which is the final active stage before the outputs. The circuit essentially consists of a switchable
regulator. Q12 {Q2} and Q14 {Q4} regulate the + and - analog supplies respectively. Q10, Q11, and
Q13 {Q1, Q3} are used to switch the regulating transistors on and off depending on the state of the
RESET line.

3.00 Digital Signal Paths

3.10 The 8031

The 8031 MPU is the heart of the D4/D5's control
section. It handles everything from keypad input and MIDI
I/O, to triggers. Note that the 8031 data buss serves a
dual purpose. This buss multiplexes between low order
addresses (1st 8 bits), and data. Latch U4 {internal to
56IFT ASIC} is used to hold the low order address half,
during 8031 read and write cycles. The (U5) {U15} is
used to hold 8031 program information. The SRAM (U6)
{U16} holds system variables, as well as user parameter
data. Z1 {Z1} provides the 12MHz 8031 clock. MIDI I/O is
handled through the 8031's built in RXD (Read Serial
Data), and TXD (Transmit Serial Data) ports. Piezo input
is handled through the regular 8031 I/O ports. Keypad
decoding, DM3AG ASIC control, and LCD output are
handled through memory mapped I/O (see section 3.12).

3.11 Reset

The reset circuit is perhaps the most singly
important circuit in the D4/D5. Failures in the reset circuit
can cause symptoms ranging from loss of battery backup
to a complete machine lock up. The circuit utilizes the
positive raw supply voltage to determine when the supply
voltage is high enough for the regulators to function
properly. Diagram Error! Bookmark not defined. shows
the sequence of events during power up. When the raw
supply voltage reaches approximately 7.2V, Q1 {Q11}
switches on, pulling the base of Q2 {Q7} low and shutting it off. This allows C32 {C106} to charge via
R23 {R126}. Once C32 {C106} reaches roughly 3V, U7 {U27A} (pins 10 and 11) switches states,
Alesis D4/D5 Drum Modules Service Manual 3
Diagram 3
02/19/03