Retroaktiv MPG-70 User manual

VERSION 1.0
MPG-70 DIY KIT BUILD GUIDE

RETROAKTIV MPG-70 OWNER’S MANUAL
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This guide is intended to help guide builders through the process of assembling, pro-
gramming, and testing the Retroaktiv MPG-70 Super JX controller DIY kit. This kit re-
quired soldering skills, and the ability to read schematics, a bill of materials, and identify
SMD pas. If you do not have experience with these things, please seek the assistance
of a person who does.
The following items are needed to assemble this kit:
• Solder
• Flux
• Multimeter or oscilloscope
• ISP programmer (USBTiny, for example)
• Philips head screwdriver
• SMD tweezers
•
When you receive your kit, the enclosure, rear plate, and front panel will be screwed to-
gether, and the PCB, and all other pas will be inside of the enclosure.
The faceplates should be washed with a so cloth and some water, to remove any resi-
due from offgassing of the enamel. This may not be necessary, but it is recommended.
Once cleaned, the panel and enclosure pas can be set aside.
PCB Assembly:
For the easiest assembly, build your PCB in the order laid out in this guide. Since some
pas are close together, such as in the power suppy, assembly will be easiest if you as-
semble in a paicular order. It is recommended that you clean your work of flux as you
go, as this will guarantee that no tiny pools of flux are overlooked. Flux can cause er-
roneous readings in the sensitive multiplexer circuitry, so it is critical that your work be
clean.
The first component to solder to the PCB is the Atmega128 processor. While this com-
ponent looks daunting, applying it to the PCB can be quick and easy if the proper sol-
dering tip is used. For more information about proper tips, and videos of these tips in
action, please look at this page at the Hakko website.

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The ATMEGA128 PCB footprint.
The Atmega128 has 3 dots imprinted on the top of the casing. These dots form a tri-
angle that points to pin 1, which is indicated by the center dot. The center dot on the
processor should match with the pin 1 indicator dot as shown above. (Dot to the upper
right of U13) Take care to inspect your work and be sure that there are not pins shoed
on U13.
Once the main processor has been soldered and the flux has been cleaned, move on to
soldering the ceramic resonator. Though the resonator is small, it is not difficult to sol-
der. Apply flux to the 3 solder pads on the PCB, and using tweezers, place the resonator.
Orientation does not maer. With a bead of solder on the tip of your iron, run the bead
down the le and right sides of the resonator. You will see the solder adhere to the pad
and the 3 gold contacts on the resonator.

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Resonator soldered in place.
• STEP 2 - ICs
Next, solder the 6 CD4067s, the CD4051, the two OPA opamps, the 74LS04, and the op-
to-isolator ICs. Take care not to leave flux around the pins of the ICs, especially on the
CD4067s, as this will cause erroneous readings. The most common mistake when build-
ing these is to leave a mux pin unsoldered, or to have a cold joint on a mux pin. When
this happens, it will cause multiple parameters to flash across the display, or the param-
eter associated with the unsoldered pin will flicker on the screen as you toggle other
parameters. For best results, check your work using a microscope or other magnifica-
tion.
The opto isolator is SMD, but the legs are bulky and they will absorb heat. This means
that you should not drag solder this IC, and you should use more solder, so that you en-
sure a good connection. Any bad solder joint on this IC will result in MIDI IN not working.

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• STEP 3 - DIODES, RESISTORS, INDUCTORS, FUSE, & CAPACITORS
Next, we move on to soldering the resistors and capacitors. Use the BOM to locate and
solder all resistors and capacitors. Note that R100 and R112 (the resistors that set the
regulator output voltage) are 0805 resistors. Be sure to use the 0805 resistors here.
Diodes are marked with a bracket which indicates the direction of the cathode (black
bar). A bracket such as ] indicates that the bar should point to the right. A [ means
that the bar should point to the le.
D7 is a schoky diode and the cathode marking is tough to read. Using a magnifier, look
at the printing on the diode. The side with the “1” printed on it indicates the bar. Double
check your orientation when placing this pa, as a mistake will mean that your power
supply will fail.
The fuse is a 1206 package and is all white. Place this above the power supply.
Place the 2 small inductors (0805 package, dark grey) L1 and L3.
Place all 0603 capacitors according to the BOM. Do not place any electrolytics yet.
When you have reached this step, clean all of your work of flux.
Now place the 22uF and 10uF electrolytic capacitors. Do not place the large 680uF and
the large inductor. These pas get placed last.
• STEP 4 - SWITCHING REGULATOR
This step is very impoant. The regulator is the key to geing stable readings and sta-
ble operation. Sta by using a light abrasive and lightly clean the legs and fin of the
regulator. You want to assure that the solder joints in this pa are very solid. Once the
metal pas that will be soldered to are clean, apply flux to the pads and set the pa
on the PCB. Do not drag solder this pa. To hold the pa in place, solder pin 1. Do the
same for all 5 legs, taking paicular care on pin 3, the center leg. This pin will require
that you linger with the soldering tip for a bit longer, since this pin is directly connect-
ed to the heat sink fin, and the joint will absorb heat, thus taking longer for the solder
to form a proper joint. To finish, apply a genereous amount of solder to the fin, making
sure that solder is flowing beneath the pa and forming a good ground joint. This is
very impoant.

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• STEP 5 - LARGE INDUCTOR & FILTER CAP
Finally, solder the large inductor and the 680uF filter cap in the PSU. Note that you must
use a fair amount of solder to aach the large inductor to the pads. Be generous with
the solder here. When happy with the inductor mounting, solder in the 680uF filter ca-
pacitor. Clean your work, and this will conclude the SMD soldering poion of the assem-
bly.
• STEP 6 - DIN JACKS, PEDAL JACK, & ISP HEADER
Next solder in the pedal jack, the 5P DIN jacks, and the 6P DIN jacks. These all go on the
boom side of the PCB (The side with the SMD components and the processor). Notice
that the pedal jack will snap into place because of the kinked legs.
The ISP header should also be soldered to the boom side of the PCB. It is impoant to
solder these pas now, because once the PCB is aached to the panel, accessing the
top side of the board will be impossible.
• STEP 7 - SLIDERS AND ROTARY POTS
In this step, we must place all of the sliders and all rotary pots EXCEPT THE 2 TALL TRIM-
MERS AND ENCODER. Note that we are NOT placing the 9 switches, the two tall trimmers,
the encoder, and the 3 red LEDs yet. This comes later.
When all pots and sliders are placed, use your soldering iron from the top side of the PCB
and solder one of the stabilizing legs (The pins that are pa of the slider chassis, not the
3 electronic pins) of each slider. This is done to hold the sliders in place when we flip the
PCB to solder the pins of the pots and sliders to the board. There’s no need to do this on
the rotary pots. Those will stay in place when you flip the board without being soldered.
Now flip the board. Make sure that the sliders are straight when you solder them in. Do
the same for the rotary pots. When this step is finished, your board will have all pas
populated except the switches, LEDs, tall trimmers, screen, and the encoder.

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All pots and sliders installed.
• STEP 8 - ATTACHING PANEL
Next we must prepare the front panel for aachment to the PCB. Begin by gathering
the 5 long screws, the 5 threaded standoffs, and the paper spacers. Depending on the
kit, you have either blue paper spacers or brown cardboard spacers. If you have blu
spacers, use 4 spacers under each standoff and thread through the panel as shown be-
low.

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Now it is time to prepare the screen to be placed. The screen has 4 pins that must be
trimmed to be flush with the PCB. This is so the pins do not make contact with the met-
al front panel. The pins should be cut using angle cuers and should be flush as shown
below.

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Now place the screen, the encoder, the tall trimmers, the switches, and the 3 LEDs. Do
not solder yet. Just fit them in their respective holes.
Once all pas are placed, place the switch caps on the switches. Be sure that the
switches are placed flush with the board and NOT AT AN ANGLE. Soldering them in at an
angle will mean that your PCB will not fit through the panel, or that your switches will
stick when pressed.
Now lower the front panel onto the PCB. Take care to make sure that the switches and
pots that aren’t yet soldered do not get pulled rom their holes. When the panel alls into
place, use the nylon nuts to hold the PCB to the protruding 5 screws under the board.
Now adjust the 3 LEDs so they’re poking through the rectangular holes. Don’t solder
yet. Be sure that the PCB is siing firmly on the standoffs and is not catching on any-
thing. Now go down the row of switches and test each one, ensuring that the fit is good
and the switch clicks up and down freely. Solder in place when you are happy with each
switch. Take care not to let the screen fall out when you flip the assembly. Then adjust
the LEDs so they are flush with the face of the panel as shown.