Repair Blog

Roland CP40 Repair

Quite old plastic unit from 1990 This unit basically converts any monophonic audio signal like voice or guitar to Midi notes (it has two different working mode). The CP-40 was part of the old Atari ST TENTRAX system along with the MC-500 II sequencer. 

What's wrong?

The unit does switch on, but no signal arrives at meter, so no Midi conversion is made. At first glance no issues: clear board, good flats, capacitors seems to be ok with ESR and no inflated ones. The unit is quite easy to open, mainly made by 2 layered boards: analog lower and upper digital. After checking the basic routine on the microphone jack input, I found no breaking, perfect soldering and correct Voltage.

The analog board is perfect, op amp no issues. The signal was going correctly from lower board to upper digital CPU which does audio to midi conversion. Interesting fact: the Midi out correctly sends out on MIDI monitor the slider Control Change, so both midi I-O and logic were no problems.  Checking also the pot sliders for volume, ohm values were ok, anyway after cleaning I switched with the DATA value one (same K, I think 100, can't remember). Followed signal thru CN5 and...

Touching the board somehow near flat made finally the v-meter doing something. First inspected CN5 ribbon but ok, anyway it's quite solid. I HATE when something works with intermittency! Just turning on the Microscope and BINGO! the Q4 transistor had a solder cold joint, you pesky dirty little rat! A quick soldering and voilà! back to life. That was not a big deal, happy to have back that little nice machine, quite funny to experiment.

■main panel features a 7-segments display, a gain peak-meter, 2 sliders and 4 membrane buttons. The CP-40 originally came with a cheap dynamic microphone but you can use any others.
Front panel terminal connectors:
- audio signal input (impedance line / Mic) .

■he CP-40 converts monophonic audio signals from microphone or line-level input sources to Midi signal in (quite) real-time. The interface is really easy, just plug the instrument into the AUDIO input, then automatically the CP converts to Midi data to a module (or synth) - the unit shows the tracked note on the display.

■ the tracking system outputs the following message:
- pitch note
- pitchbender value
- Control Change 11 (expression).
Control change #11 is the dynamic / amplitude of the signal.e

■  6 special functions:
- gain: sets the incoming signal level
- Midi channel: sets the Midi ouput channel (1-16)
- octave shift: amount by which transmitted notes message will be transposed (range +/-2 octaves)
- velocity expression: 5 modes to translate incoming amplitude to Midi velocity
- bend mode: how the CP translates the signal pitch fluctuation and how it will be transmitted to the pitch bend Midi signal
- threshold: determine the level in which the Midi note message will be generated (3 preset levels).

■Back panel terminal connectors:
- Midi input and output
- impedance switch set
- Midi merge switch set (incoming Midi data are merged to out).
Power supply is a 9V external PSU -)+ any general AC/DC PSU can work (100mA are enough) 

■Dimensions 608 mm x 281 mm x 105 mm
Weight 2.2 kg  

■ NO SERVICE MANUAL if you have it, please do contact us we will share it for free

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