The roland MC303 is a 28‑voice polyphonic sound module, with 448 sample‑based presets. The sounds are editable in real-time with knobs — the beginning of the famous GROOVEBOX series. Techno, jungle, hip-hop, acid and other dance styles from the era. Today still hated-loved machine.
I had something like a dozen of mc303, it's one of those machine that you can find anytime ad reasonable price on second hand market. I found a craigslist at a couple of bucks with a Korg DDM220
in bundle. The seller told me there was a couple of things to fix like buttons and the powerswitch. Nothing too complicated.
After a couple of days, it arrived, but sadly the package seemed damaged. I brought it to the lab, where I hosted Vito a Stray cat from CORLEONE (yes, that Corleone).
The Korg is indeed ok, but the Roland has two broken pots, including shafts and part of the knobs. I was not really ok with that, but I managed at least to find the plastic parts of the knob.
Except this, tact switches are quite all dead, the encoder seems to be sluggish and the MC303 remains powered even in both powerswitch position.
UPPER First a good cleaning at the machine with soapy water. Note that you have to remove all knobs with care, the encoder wheel with its washer (with a plier).
UPPER - There are only a couple of screws under the groovebox, the main board has four screws also. For easier accessm for removing all flats is recommended, but just one is really mandatory to access to lower board (indicated on the picture). You can take advantage to change the Cr2032 battery, it's not soldered and give a good clean to the board.
UPPER finally I have access to main board, to pay attention to not bend the Diode leds and not pry the 16 plastic pads, that seems to be fragile. A quick clean to main encoder after all that years is more than welcome with dry deoxit.
I was quite worried the wrestler-courier impact somehow damaged the mainboard with cracks, but it seemed to be ok. The 4 pins around the potentiometer were bend, thus the shaft was also askewed, nothing that pliers could not straighten up. Testing the OHM measure seemed to be coherent valued for both pots, phweee this was my worst fear.
Inspecting the rest of the board revealed nothing particular. Now the tact switches.
UPPER: There are A LOT of 2 pins tact switches in the MC303 (don't get confused with relative LED pins when desoldering) about 35. I dohighly recommend a desoldering gun at 300 degrees Celsius for a faster and clean job. The board is quite strong and you should not lift any welding pad.Now last thing to do: the powerswitch (btw the PSU is VDC negative center like many Roland).
UPPER the Mc303 remained always on ON position because the powerswitch has been somehow bypassed wiring two pins of it... Gosh! Once removed that fab mod, I desoldered the ALP powerswitch (marked as useful Roland code "SPUN19" on the relative service manual ,you will find at the end). The tiny metal plates were totally oxidized with some black burnt like marks, of course it would never make contact in this condition. Disassembling the powerswitch requires to be quite careful especially with spring system.
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