General Description; Power Supply; Battery Backup; The 8031 Micro Controller - Alesis MMT-8 Service Manual

1.00 General Description

The MMT-8 MultiTrack Recorders power lies mainly in the sophistication of it's software. The
most powerful troubleshooting tools available to the technician are the a good working knowledge of
the MMT-8's operation and the software history in section X.X. Most problems with the MMT-8 arise
from either user error, or older software. The hardware is very simple and should normally prove to
be problem to troubleshoot. Please note here that there are sveral revisions of main PCB and 2
revisions of keypad boards. While latest versions of the main PC Board include most of the
hardware updates, older board revisions will require some additions to bring them up to the current
factory specifications. These updates are discussed fully in section X.XX.

2.00 Power Supply

2.10 Battery Backup

Battery backup is actually more complicated than it might first appear, as it depends on a
good system reset (see section X.X for details) in order to function properly. The actual backup
circuit consists of a battery (3V - 3.6V Lithium), a 10K resistor (R76) for checking standby current
(see below), a "steering" diode (D5), a filter capacitor (C13), and a transistor/resistor/diode
combination (Q11, R79, D6) that acts as a steering diode. This combination may be missing on
older board revisions, and must be installed (see section X.X) to prevent data corruption due to a
significant difference between V cc , and the amplitude of the data buss.
SRAM standby current should always be checked. While the unit is off, check the voltage
across R76. If the voltage is higher than 80mV (specification, although a 1 to 20mV range is more
normal) then a problem exists. Usually it indicates a bad (or simply wrong) SRAM, or a short,
somewhere along the MEM PWR line. Note, that for a short time, Sony 58256-PM (high power)
SRAMs were being installed at the factory, causing batteries to drain in about 1 year. They should
be replaced with low power versions (58256-LP) when found, in order to eliminate excess battery
drain. We are currently using Hitachi 62256ALPs as replacements.
CAUTION:
Danger of explosion if battery is incorrectly replaced. Replace only with the same type or

3.00 The 8031 Micro Controller

The 8031 MPU is the heart of the MMT-8's control section. It handles everything from keypad
input and MIDI I/O, to sequencing. Note that the 8031 data buss serves a dual purpose. This buss
multiplexes between low order addresses (1st 8 bits), and data. Latch U11 is used to hold the low
order address half, during 8031 read and write cycles. The EPROM (U12) is used to hold 8031
program information. The SRAMs (U9, U10) hold system variables, as well as user sequence data.
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. Tape I/O is handled through the built in 8031 I/O
ports. LCD output is handled through memory mapped I/O (see section X.X). Keypad decoding
uses both forms of I/O (see section X.X).

3.10 Reset

The 8031 reset circuit is perhaps the single most important circuit in the MMT-8. When this
circuit is functioning incorrectly, problems ranging from loss of battery backup, to a complete lock-up
of the machine, can occur. A thorough knowledge of the operation of this circuit will greatly facilitate
troubleshooting this unit.
Alesis MMT-8 Service Manual 1.00
equivalent type recommended by the equipment manufacturer.
Battery Manufacturer: Tadiran
Type: TL-5101
Rating 3.6V
1