Alesis MIDIVERB IV, Service Manual

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Alesis MidiVerb IV Service Manual‘ 5 03/05/99
6.00 The Front Panel
Care should be taken any time that the front panel must be disassembled. Some
components (i.e. LCD glass and heat seal cable) are delicate, and will not stand up to a lot of
abuse while disassembled. It should be noted that while the LCD assembly is accessible at this
point, field disassembly of the LCD is NOT recommended, and front panel repairs in the field
should be limited repairing keypad failures.
The front panel contains three key elements:
The LCD
The Keypad
Display LEDs
6.10 The Keypad
The 8031 accesses the keypad via a standard row-column polling matrix. The actual
switches are composed of gold plated contact points on the PCB, and a carbon coating on the
contact points of the rubber keypad. The 8031 constantly scans the keypad for button press by
sending a low to each row, and checking for a corresponding low on any of the columns. Note
that the data encoder is also scanned in this fashion, and not all encoder failures are
necessarily caused by a bad encoder.
6.20 Display LEDs
Should one or more front panel LEDs go bad, they should be fairly easy to replace using
the disassembly procedure outlined below. If all of the LEDs are dead, then the 74HC138 (U3)
is probably bad and should be replaced first. Again this component is only accessible by
disassembling the front panel.
6.30 Disassembly
Refer to diagram 1 which shows the locations of the critical elements of the front panel
assembly. Remove the front panel assembly from the main chassis, and unplug the cables at J1
and J2. Detach the 4 metal clips from the extruded case. Remove the nylon retaining strip
freeing the plastic frame assembly. Push the frame to the back of the front panel and it should
be free to slide out of the side of the front panel.
To remove the PCB it will first be necessary to unsolder the ribbon cable connecting data
encoder to the front panel PCB. There are PCB retaining clips built into the plastic frame. Gently
push these away from the PCB, and lift the PCB away from the frame. When all six clips have
been loosened, the board should be free to remove from the frame.
To remove the data encoder it is necessary to remove the knob first. In order to do this
without tearing up the front panel, use the holes in the back of the frame to push the knob off
with a small screwdriver (see diagram 2).