MC-202 Analog User Modifications

Do It Yourself Special: FREE plans to add MIDI capability to the Roland MC-202 with the Synhouse Original MIDIJACK!

The following plans describe a method of adding MIDI capability to the Roland MC-202 with the Synhouse Original MIDIJACK. The Original MIDIJACK converts the Roland MC-202 into a MIDI analog synthesizer module, allowing you to use a proper MIDI sequencer with full editing capabilities instead of the tiny internal sequencer. The MC-202 is especially well suited for this modification due to the tiny size of the MIDIJACK circuit board and the fact that it is the first analog MIDI retrofit ever made that costs less than the instrument itself! The Original MIDIJACK will control the MC-202's internal portamento circuit to make it think that it is playing a sequence programmed with portamento so that the the MIDI notes will have the amount of glide set by the portamento pot position.

Please note that the CV/gate input jacks on the MC-202 are so poor that they are useless for most musical purposes. The incoming CV/gate signals are regurgitated through the internal sequencer, slowed-down and quantized to the poor DAC resolution of the MC-202. Thinking of using some type of external MIDI control box through these CV/gate inputs? It isn't nearly as good as using the Original MIDIJACK. The newer Synhouse technology provides much greater DAC resolution, twice the note range, and the world's fastest MIDI response. This modification reroutes the internal sequencer signals through the computer-controlled analog switching matrix of the MIDIJACK by extracting the signal and inserting the users' choice of local sequencer / tiny keyboard control or MIDI. There isn't any space on the MC-202 to easily install any type of MIDI retrofit, but with some creativity and careful modification, it is possible to install the Original MIDIJACK, making it the world's only internal MIDI retrofit for the MC-202.

You may be able to do this yourself if you have experience with electronic repair and the soldering of wires and circuit boards. If not, it is highly recommended that you ship the unit to Synhouse L.A. for a quick, low cost Factory Installation. This way, the Original MIDIJACK can be properly installed in the Roland MC-202 by Synhouse without risk. This one is priced as a synthesizer which does not have CV/gate jacks (for the reasons stated above) and the price for the labor is $99 plus current costs for the new external power supply required for the MIDI upgrade. This price covers the cost of the labor and supplies used for the upgrade but does not cover shipping the synthesizer round-trip to Los Angeles, California. The user must also purchase the Original MIDIJACK from Synhouse at current pricing. These prices are current as of the time of this writing, but check with Synhouse Factory Installation for the latest information on the pricing and availability of this service. The customer is not required to supply schematics for this particular installation, as it is well known to Synhouse. The work will be performed in ten business days or less.

For self-installation, it is best to print these notes out on paper to look at while working on the instrument and make notes and check off the steps as you go. As with any project, it is best to completely read and understand each step of the instructions before starting. The particular installation on which this document is based was on Roland MC-202 serial #327400, other revisions may be different.

All repairs and modifications made to your instruments will be done at your own risk and Synhouse Multimedia Corporation assumes no liability for personal injury caused or damage to equipment or loss of use caused directly or indirectly by the use of these plans. If in doubt, don't do it!

Instructions:

1) Be sure to have the correct tools and supplies for for the job. If you do not have them, get them. You will need a regular size Phillips screwdriver, a smaller size Phillips screwdriver, needlenose pliers, wire cutters or other flush cut nippers, a hobby knife such as an X-Acto, scissors, a soldering iron, solder, electrical insulating tape (or heat shrink tubing if you have it because it never becomes sticky or falls off), and a black Sharpie permanent ink marking pen. You may wish to use a Dremel Moto-Tool to carve out the plastic to make way for the DIN jack and circuit board, and a low-speed electric drill with a 1/8" or similar size drill bit to drill holes for the 4-40 hardware used to mount the DIN jack. A DMM (Digital MultiMeter) with the continuity test function is absolutely required to do this job. It is the only sensible way to locate and verify the proper points.

2) Fully test the Roland MC-202 to be converted to MIDI. Be sure that all functions work. If it doesn't work properly without MIDI, it certainly won't work with it.

3) The installation of the Original MIDIJACK in a Roland MC-202 is fairly straightforward from an electrical standpoint. The difficulty comes when trying to fit the new MIDI hardware inside the tiny plastic case. The installer must cut copper traces on the circuit board to isolate and access the correct DIN sync I/O signals. This modification reroutes the internal sequencer / tiny keyboard signals through the computer-controlled analog switching matrix of the MIDIJACK by extracting the signals and inserting the users' choice of local internal sequencer / tiny keyboard control or MIDI. The whole MIDI conversion job might take 2-3 hours, depending how crafty you get chiseling away bits of plastic to get a good fit. This is one not to be rushed.

4) Remove the seven Phillips screws that hold the lower case in place. Remove this piece.

5) Turn the instrument upside down and shake out any dust and debris that may have accumulated inside the instrument over the years.

6) Remove the knobs and slider caps and remove the upper case as well. Place the board on a soft nonconductive surface.

7) Determine the place where the MIDIJACK circuit board and DIN jack will be mounted and test fit the board into its' correct place inside the case. You may wish to use different mounting hardware for a low-profile installation as described in the Original MIDIJACK Advanced Installation Manual. This will be the most difficult part and it is left entirely up to the installer. The easiest place to mount the board and DIN jack would be inside the battery box. The Original MIDIJACK-equipped MC-202 cannot be battery-powered. It must be used with a new external power supply to get the full 10-1/2 octave MIDI note range. The test unit done by Synhouse for the purposes of writing this article was done another way, where the battery box was left empty and the MIDI input DIN jack is on the lower panel piece in the right rear corner facing out to the right hand side, and the MIDIJACK board is mounted with smaller 4-40 hardware under the control panel just to the rear of the VCA section, as seen here in MC-202-pic1:

This makes for a cleaner installation, but more than doubles the amount of time required to do the work. This spot is a very tight fit and much care must be taken to get the holes drilled in precisely the right places and to avoid short-circuits. There is literally no space for the standard MIDIJACK board configuration here so the aluminum mounts were removed and shorter ones were held in place by epoxy glue. Some electrical insulating tape was placed over the top of the electronic components beneath the MIDIJACK board to eliminate the possibility of short circuits if the epoxy came loose and the board came down. This way, no matter, it has nowhere to go, it is trapped in the 10 millimeters of space under the control panel. The Original MIDIJACK accessory packet has paper drilling templates to ease drilling. Once carefully taped in place, the holes may simply be drilled through the paper. Do not use a high-speed drill when drilling plastic. The chassis pieces of the MC-202 are made of soft plastic and a high-speed drill will build up friction, generate heat, and burn the plastic permanently. Drill at the slowest speed available. The perfect size drill bit for the switch stem and two screw holes is 9/64", and the perfect size for the scale adjust trimpot is 3/16". Drill the holes. If your drill is not slow enough to safely drill plastic, you can use an X-Acto knife to make the holes by twisting. This is a little more time-consuming, but works well if you don't have a drill to use. You can use a standard X-Acto knife blade with the sharp point and twist it in place until it starts to dig a little hole. When it gets close to reaching the other side, you can look outside and see the tip coming through and dig back from the outside as well. A perfectly round hole can be shaped using this technique.

8) Obtain a new power supply to use the MC-202 with MIDI. The original BOSS PSA or Roland AC adapter has an output voltage that is too low for the MIDIJACK. The MIDIJACK must have at least +12 volts DC input to allow it to be stable and put out the top MIDI note 127 which is +10.58 volts. The original Roland unit was said to be +9 volts DC, but when measured under load it was found to be +11.53 volts and dropped after some time. The MC-202 uses an old but clever powering method which allows portable operation with 6 "C" cells, which comes out to only +9 volts total if the batteries are good. When an AC adapter is plugged in, the DC IN jack switches out the connection between the batteries and the synthesizer circuitry. If this AC adapter provides only +9 volts, that is fine, or if the AC adapter provides +17 actual volts that is okay as well.

The MC-202 has a DC-DC converter that steps up the voltage to about +20 volts unregulated, then runs it through a linear voltage regulator that puts out the regulated +15 volts that the analog synthesizer circuitry runs on. To check and see how it is working, both before and after you replace the original power supply, measure the voltage:

a) Check the unregulated input voltage at the DC INPUT jack on the MC-202. With the instrument turned on, this will show you the voltage under a real load.

b) Check the regulated +15 volt supply which can be found on IC 21 pin 16, which is a Curtis Electromusic CEM 3340 VCO chip. It was found to be approximately +15 volts.

The standard MIDIJACK installation connects to the regulated synth supply, usually +12 or +15 volts, but in this case, it was found that the MC-202 was not designed to provide the extra 35mA required by the MIDIJACK. The voltage on the +15 volt supply begins to drop as soon as the MIDIJACK is connected, a sure sign that it will overload it and cause damage. This is no problem, because the MIDIJACK has a power supply that has better line and load regulation than the MC-202 anyway, and can operate on a much lower voltage than the +21 volts going into the MC-202 regulator. For this reason, we will draw the power for our new MIDI system from the unregulated DC IN jack. The original unregulated power voltage is too low, so we will use a new power supply. You must use a power supply which is at least +12 volts DC when loaded (connected to the running synthesizer), and a little more is better. A +14 VDC or +15 VDC power supply with a current rating of 300mA or higher is best. This must have a co-ax type of power connector with an inside diameter of 2.1 mm. The center must be -negative and the outside +positive. This is not the best way to wire a power connector because if it is dropped on a grounded metal surface the outside will touch and short circuit into the ground, but that is the way Roland did it on the MC-202. Most power supplies you will be able to find will be wired in the opposite polarity, but it is easy to cut the connector off and reverse the polarity for use with the MC-202. Be careful to insulate the wires after resoldering. This is such a common type of part that you may already have one in your junk box, but in the USA, a good and friendly source for this part is Jameco Electronics. The Jameco catalog number is 129314. It is a +14VDC@360mA AC adapter which costs $4.95, but they have many more that will work just as well. The power supply used by Synhouse for this installation was catalog number DCTX-1436 for $3.50 bought from All Electronics. They are an equally friendly source of electronic supplies, but their stock changes daily, and the +14VDC@360mA supply purchased and used here has not been available for years, but they have others that may work just as well. When this one was used by Synhouse, the actual voltage when loaded was +16.6 volts and the MC-202 actually drew less than 100mA. Obtain the correct power supply, wire it with the correct power plug with the correct polarity, and test it with your MC-202 before installing the MIDIJACK. Be sure to remove the batteries from the MC-202. It will no longer be operated on battery power. Your new power supply will cost less than one set of alkaline batteries and, unlike the batteries, this new power supply will most likely last forever and won't fill up landfills with toxic dead batteries.

9) The black and red wires must be soldered in place to get the ground and power for the Original MIDIJACK. The correct soldering spots are on the lower side of the board beneath the DC INPUT jack and POWER ON/OFF switch as seen in MC-202-pic2:

The ground wire is going to the tip terminal of the power jack. Solder the MIDIJACK #1 black wire to this point. The power wire is going to the other side of the power switch so the MIDIJACK may be powered down with the MC-202. Solder the MIDIJACK #2 red wire to this point. In the photo you can see the wires you are adding are the thin ones.

10) The MIDIJACK #3 blue wire must be connected next. You must move the top board to expose the circuitry below on the bottom board. Do not try to unscrew it. The correct way to do this is to use pliers from below and pinch the tips of the nylon standoffs to release the catches so you can push the tips through. Later you can just press them back in place with the original snap fit. Locate IC 18 on the main lower board of the MC-202. It is an 8-pin chip. Look at the bottom of the PCB. Note that pins 1 and 2 are connected by the lower trace. You will leave them connected. Notice that the solder pad and circuit trace go to the side and cross through a via to the top. On the top the path goes off to other parts (such as the portamento dual pot VR5, you can buzz it out to see for yourself). Cut the trace on the top side with an X-Acto knife so only pins 1 and 2 are connected to each other but to nothing else. One good way to do this is to score two parallel grooves and then lay a very hot soldering iron down on one side of the tip between the two cuts. This heat will ruin the glue holding the center patch and delaminate it leaving the two sides isolated. This is often a lot less effort than digging and digging a groove to break a circuit trace. Solder the MIDIJACK #3 blue wire to pins 1 and 2 below as seen in MC-202-pic3:

11) The MIDIJACK #4 white wire must be connected next. Find the two pins of the portamento dual pot VR 5 that are shorted together which used to be connected to IC 18 pins 1-2 (you can buzz it out to see for yourself). Solder the MIDIJACK #4 white wire to these two pins on pot VR 5 as seen in MC-202-pic4:

12) The MIDIJACK #5 yellow wire must be connected next. Find pins 34 and 38 of IC 8. This is a square surface-mount NEC chip on the lower side of the board. Pin 1 is in the corner and the numbers go up counterclockwise from there. Locate pin 34 as seen in MC-202-pic5:

Cut the circuit trace from IC 8 pin 34. You must solder the MIDIJACK #5 yellow wire to pin 34 now, but the wire is too thick and not good for fine soldering. No matter, we can make a thin extender. Solder the MIDIJACK #5 yellow wire to a small piece of stiff solid wire, such as one of the leads cut off a resistor or capacitor. This will be your thin extender to be connected to the chip. Solder this MIDIJACK #5 yellow wire with the new thin extender tip to pin 34 now. Please be very careful not to apply too much heat to this chip.

13) The MIDIJACK #6 green wire must be connected next. It must be connected to the trace that was cut from IC 8 pin 34. If you try to scrape off the soldermask and solder to the trace itself, you will encounter two problems. One problem is that it is difficult to solder onto bare copper. This is why circuit boards are plated. The second problem is that a thin trace has very little mechanical strength. The solution is to solder your wire onto some component attached to the trace. In this case, you can look for resistor R 234 on the top of the board near the VCA ENV / GATE slide switch.

A note about resistor R 234:

Sometimes this resistor cannot be found due to variances of the silkscreen on the Roland PC board. It might appear to be R 34, as it did the first time it was done here at Synhouse, or it might appear to be R 23, as it did to one customer. The Roland schematics for the MC-202 refer to this resistor as R 234 and that is what it is.

Just be aware that your particular silkscreen might make R 234 look like R 23 or R 34. It is R 234 and the other end of it, the side that we don't connect to, is connected to R 235.

The upper lead of

resistor R 234 conducts to the trace below, but there is a problem. The problem is that these are Panasert type resistors. These were developed by Panasonic in the early 1970s for consumer products. They have two attributes different from other resistors. One is that they are preformed and precut. They are bent into a shape that allows them to be snapped into the board before soldering in a vertical position which occupies less board space. Another thing about them is that they are painted over the metal surfaces with a nonconductive paint. In manufacturing and use, this is great, the board can be stuffed with resistors, overstuffed to the point where the leads are touching which is okay because they won't short circuit through the nonconductive paint. In repairs and modification, it is irritating, because when you are trying to probe the board to buzz out a circuit on a board with no silkscreen such as a Korg Synthe-Bass, you can't tell unless you scratch the paint off of each lead. For this MC-202 R 234, you must scratch off all the paint on the upper lead of R 234 before soldering the wire onto it. Solder the MIDIJACK #6 green wire to this point on R 234 as seen in MC-202-pic6:

14) The Original MIDIJACK will control the MC-202's internal portamento circuit to make it think that it is playing a sequence programmed with portamento so that the the MIDI notes will have the amount of glide set by the portamento pot position. We now need to make a simple circuit to act as the interface. Locate IC 14 on the main board of the MC-202. It is a 14-pin chip. Find the circuit trace from IC 14 pin 5 on the lower side of the board. Cut the trace. This will disconnect IC 14 pin 5 from the circuit. There will now be 3 new connections made to IC 14 pin 5. Take a new 10K resistor (a 10.2K resistor was used here) and solder one end of it to IC 14 pin 5 and the other end to IC 14 pin 14. Do this on the lower side of the board. Take a new switching diode (a 1N914 or 1N4148 will work fine, one of these was included with your Original MIDIJACK accessory packet) and connect the anode end (the end AWAY from the little black band) to IC 14 pin 5. Connect the cathode end of this diode (the end WITH the little black band) to IC 8 pin 38 (this is the chip on the lower side of the board). This is where the IC 14 pin 5 trace used to go. Please be very careful not to apply too much heat to this chip. Take another new switching diode (a 1N914 or 1N4148 will work fine) and connect the anode end (the end AWAY from the little black band) to IC 14 pin 5. Connect the cathode end of this diode (the end WITH the little black band) to a new piece of wire. You can cut off the MIDIJACK #7 brown wire (not needed for this installation) and use that. Strip the insulation off the other end of the wire and twist it until it is thin enough to insert into a via on the Original MIDIJACK board. A via is a place where a hole has been drilled from the top of the board to the bottom of the board and plated through to pass the signal between the top and bottom sides of the board. This via you must locate is on the top of the board 4 millimeters to the left of the white silkscreen letters that say R 22 beneath resistor R 22. On the bottom of the board the silkscreen says COPYRIGHT and this particular via goes through the "C" in COPYRIGHT. Insert the new wire from the top and solder from the bottom. Trim the excess length below. The other end of this wire was already attached to the cathode end (the end WITH the little black band) of the second of the two new diodes. This will provide a control signal to turn the portamento on when the MIDI on mode is activated. When all of this soldering is completed it will look something like this setup shown in MC-202-pic7:

These leads are exposed only for the purposes of taking this photograph, they were insuated afterward. You must cover all of these leads with electrical insulating tape (or heat shrink tubing if you have it because it never becomes sticky or falls off) to prevent short circuits once the case is squeezed back together.

15) The Original MIDIJACK hardware packet contains nylon cable ties which should be used to tie the MIDIJACK wires into little bundles and to attach them to the factory wires inside the MC-202 now that all connections have been made. This will secure the MIDIJACK wires to the inside of the chassis so they will not pop up while you are struggling to get the case back together without wires showing through the slots of the sliders once the instrument is returned to service.

16) Carefully examine all soldered connections for possible short circuits before closing the instrument. This will become critical when the case halves are pressed back together.

17) Reassemble the case, making sure that the screws are tight.

18) This installation can be completed in 2-4 hours. This Roland MC-202 operation is tricky, so extra time spent making a perfect installation is time well spent.

Performance tips:

With the Original MIDIJACK, the Roland MC-202 is perfect for live performance with real-time hands-on sound tweaking of the analog synthesizer voice while it is controlled by a MIDI sequencer. When the Original MIDIJACK is in MIDI off mode, the MC-202 returns to normal use with the internal sequencer and external DIN sync capabilities. The user can select either mode at any time.

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