Sequencer Alesis MMT-8.
Repair, modification.
Please read this first.


This article represents authors private opinions and is composed based on his experience with the device as well as various official and unofficial sources.
The author is not responsible for any consequences and damages caused by user attempts to repair or modify the device.

Alesis MMT-8

Alesis MMT-8 was developed at the end of 1980s and assembled in enclosures of a light or dark color.
There are two main board revisions: G (the earlier one) and H.

The device is an 8-track sequencer based on the Pattern - Song principle and its architecture is very similar to the HR-16 drum-machine of the same vendor. It looks like the device is designed to be used along with this drum machine (its outlook is one more argument for that) as a slave one because it lacks a possibility of controling the playback speed and its memory size is pretty small.

Small memory size of this device was a reason for extending it in a factor of 8 based on software and hardware upgrade of Exosba-8 without any significant mechanical works. All modifications are 100% reversible.






Hidden Keys

Below is a list of keys for activation of hidden functions
(function description is provided for software version 1.11 and can differ from earlier versions).



Press and hold the following keys at power-up
"ERASE" + "PAGE DOWN" + "PAGE UP" Clear memory/Reinitialize system
"QUANT" + "LOOP" Self test*

* Warning! The self test will erase all internal memory (equivalent to reinitializing).
To perform the internal diagnostics, connect a MIDI cable between MIDI in and out. Connect a 1/8" cable between TAPE in and out.

1. ROM Test: Tests EPROM for errors.
2. RAM Test: Tests SRAM for errors.
3. LED Test: Lights up each front panel LED for a couple of seconds.
4. MIDI I/O Test: Tests MIDI input/output functions.
5. TAPE I/O Test: Tests Tape input/output functions.



In work mode:
"NAME" + "TEMPO"
"NAME" + "CLICK"
"NAME" + "CLOCK"
Show device developer names








Disassembling


Enclosure (4 screws):

Disassembling of Enclosure



Make sure to memorize or mark the contacts order:

Mark of conntacts



Main PCB:

Main PCB



Speaker leads:

Speaker









Replacing the power connector


The first PCB revision G was equipped with 1/8" power jack (type A in Alesis's terminology):

Power 35 Rear


Power Connector 35 Power Connector 35 ext



It can be easily replaced with more common type B connector used in all later models.

Power Connector ext Power Connector



One needs to make some holes in the device case and its back panel a bit wider.

Case Back Panel


Power New Rear









Replacing a half-period rectifier with a bridge one

Since revision G of PCB uses only 5V voltage, replacement a half-period rectifier with a bridge one is beneficial for its efficiency.
However, in case of lower mains or external power adaptor voltage this replacement may result in a less stable device start.

Diode to Bridge


Case Back Panel



PCB revision H has additional negative voltage module for adjusting the LCD contrast. Hence, the above modification is only possible if a newer LCD is used (which does not require any negative voltage).







New SRAM Supply Circuit (from Alesis)

The new SRAM powering circuit supplies a solid 5V to the SRAM, preventing input data from being higher in amplitude than the supply voltage, which can cause corruption of data. First, remove the original diode (D15), then install the new circuit.

The installation of this circuit is highly recommended and is absolutely necessary if a 58257 SRAM is installed in the unit. This is because the '257s are much more sensitive to supply voltage compared to the older '256 SRAMs.

SRAM Supply New








Fixing the PCB revision G routing error

Revision G of the PCB lacks a connection of U6 pin 20 with +5V.

It was fixed by soldering a wire jumper on the back side of the PCB.

PCB error









Replacing the LCD

The display is attached to the top of the device case with 4 screws.

Display


Before replacing the LCD make sure to disconnect its signal cable.

Attention! Make sure to memorize or mark the contact's order.









Increasing memory size (Exosba-8)

To increase the memory size in a factor of 8 we developed special software and hardware based on Exosba-8.
It consists of:

Hardware module containing RAM IC along with necessary passives,
Embedded into MMT-8 OS bootloader for interfacing with extended memory.

Simply speaking, the modification can be viewed as extending the device to 8 sequencers MMT-8 (out of which just one can be used at each moment of time) so that memory contents of any one of them can be copied to all other ones in a sequence.


Exosba-8


For this modification, one should solder 4 wires to the PCB, cut one PCB trace on its back, mount a jumper and remove one resistor:


Revision G:

Exosba-8 PCB Rev G, Top
View (download)
2288x1712
Exosba-8 PCB Rev G, Bottom
View (download)
2288x1712

Revision H:

Exosba-8 PCB Rev G, Top
View (download)
2288x1712
Exosba-8 PCB Rev G, Bottom
View (download)
2288x1712



Extract old chips from their sockets and insert the new ones.
To remove old chips a special extracting tool can be used or just a screwdriver. Be very careful by extracting the chips and avoid bending their pins.

Extractor Screwdriver


At power-up the bootloader will offer to select one of two options:
Proceed with the work mode
Copy memory data**

**Warning! The copy operation erases all previously stored data of the target device.

Bootloader interface is implemented with keys Track1 Track8. Follow messages displayed on the LCD and take the blinking LEDs into account.

After selecting the mode follow the messages displayed on the LCD.

Prior to passing a control to the main MMT-8 program the bootloader will print a message on the LCD and pause for some time providing a possibility for pressing hidden key combinations.







Article in PDF format.






The result obtained after these enhancements is available on the Video, web-page, or directly here.







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Alesis MMT-8 repair modification modernization increasing memory size exosba-8 replacing the power connector replacing the lcd display


Copyright © 2022 by Dmitry Dubrovenko.