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The Chroma CPU Plus (CC+): Installation Instructions

by Sandro Sfregola [21010294] <>
and David Clarke [21030085++] <>

Table of Contents

December 2006 (Rev 1.1)

Foreword & Introduction

Congratulations on your purchase of a Chroma CPU Plus (CC+).

This document is intended provide guidance on the installation of the CPU board (and cables) as well as to provide information on the new features and how existing documentation does (or does not) reflect the operation of the new interface.

Each CC+ unit was assembled and tested before shipment, and comes pre-loaded with 4 banks of patches.

If you encounter any difficulties with the received materials, please contact:

For queries on general usage or requests for additional features/changes to features, it is probably best to have those discussions in the ChromaTalk forum so others can also participate.

The CC+ is intended to be a fully functional Rhodes Chroma and Rhodes Chroma Expander CPU board (unless specifically noted otherwise, references to "Chroma" are intended to refer to both the Chroma keyboard and the Chroma Expander). In addition to serving as a replacement for failed or damaged original Chroma boards, the CC+ also provides the following additional new functionalities:


Installation can be done without having prior electrical experience as no soldering is required. A complete installation will take 20 to 30 minutes.

To install the CC+, a screwdriver is required to open the case, remove the existing CPU board, and install the new components.

For those already very familiar with installing/removing boards from the Chroma - a general summary of the required installation steps are:

Details of these elements for those less familiar with the Chroma are contained in the following sections.

NOTE: Before opening the Chroma it is strongly recommended to back up any programs/settings from your current CPU board (e.g., use the tape interface or the MIDI SysEx interface to save any/all programs.)

If you will be using the CC+ with an external MIDI interface (like the Syntech/KMX interface), it is also recommended that you write down the exiting settings in use for those interfaces (for instance, for the Syntech interface, programming mode can be entered by pressing Set Split 46 or "46", depending on the version of firmware installed).

Unpacking the CC+

The CC+ package will come with:

If the optional Interconnection Kit was also purchased, the kit will also include:

One package of mounting hardware (with the necessary installation components) is also provided.

Carefully open the cardboard shipping box to reveal the contents and confirm that the expected items have been received.

Figure 1: Packaged CC+; Figure 2: Opened CC+ Box

Figure 3: Unpacked Components

It is recommended that the CC+ be left in its antistatic bag until just before it is placed in the Chroma.

Removing the Old CPU Board

To perform the upgrade, the Chroma will need to be opened to expose the location of the existing CPU board.

To do so, start by ensuring that the power to the Chroma is turned off, then unplug the power cord.

A disassembly procedure is provided in the Rhodes Chroma Service Manual (ref: Section 3 of that document). To recap that material, remove the nine screws from the back of the unit and the four screws holding down the front edge of the top panel (screws 1-9 and 11-14 as shown in Figure 4).

NOTE: Screw #10 holds a ground wire to the cover with a nut. Only remove this screw if it is desired to set the panel aside to allow for more working space.

Figure 4: Location of Rear Panel/Top Panel Screws

If you are using an Expander, remove the two screws that hold down the middle of the front panel, as below:

Figure 5: Location of Expander Front Panel Screws

To gain access to the CPU board, remove the 4 screws holding the front panel in place (screws 15-18, as shown in Figure 6).

Figure 6: Front Panel Screws

The front panel can now pivot upwards, and will rest in an open position as shown in Figure 7.

Figure 7: Pivoting of Lid, and Access to CPU Board

It is the 'computer board' which is of interest.

If possible, remove the two AA batteries then grab the ribbon connectors by the plastic shroud on the I/O board and pull outward to disconnect. (Holding the connector plastic between your thumb and forefinger and pulling with a slight 'wiggle' works well).

Early Chroma units (using the white 'ARP' boards) may have an additional (soldered) wire connecting the CPU board to the I/O board. This wire (shown here, going from pin 10 of Z2 on the CPU board) will need to be snipped at the I/O board end.

Remove the four (4) screws holding the CPU board in place. Before removing the final two screws, be sure to support the CPU board (to keep it from sliding/dropping when the last screws are removed).

At this point in time the old CPU is completely removed from the Chroma.

Installing the New CPU Board

European Customers: see Appendix for modified instructions.

Installation of the new board is essentially a reversal of the steps above. As the new board is shorter than the original, a set of support rails will be used to allow mounting.

The rails should be installed first. Install the rails with the blackened end closest to the I/O board. You can use two of the screws removed from the original CPU board to attach the right hand side of the rails. Use a provided 'standoff' (see inset) to attach the left end.

Figure 8: Installation of Mounting Rails

Before opening the bag containing the new CPU board, discharge any static which may have accumulated on your body by touching a known grounded item (such as the chassis of other nearby equipment which has a 3-prong power-cord attached).

Open the antistatic bag and place the CC+ on the rails. Using the supplied hardware, install the CC+ so that the ribbon cables are in the same general orientation as the old CPU board. The CC+ is mounted with 1/4 inch screws and a washer, as shown in Figure 9.

Figure 9: Installed CC+ Circuit Board

The next step will be to connect the ribbon connectors from the CPU board to the I/O board. You will note that the CC+ does not have the same plastic shrouds on the cables as the original CPU connectors. Remove the protective foam installed on the cable ends for shipping and use your thumb and forefinger to guide the insertion of the pins (ref: Figure 10). Exercise care so as to not bend the pins while they are being inserted.

Figure 10: Installing Ribbon Connectors

At this point in time, the CC+ is fully installed. If no cabling was purchased, you can proceed directly to the "Checkout of CC+" section.

Installing Internal Cabling

While it is possible to use the CC+ without an interconnection kit - the kit is recommended to facilitate connection of MIDI to the CC+, and allow the new MIDI features to be easily accessed.

The internal cabling connects to the CC+ and terminates on the rear panel of the Chroma. In addition to the MIDI signals, this interface also terminates serial display features in support of future feature additions to the CC+.

To install the internal cabling, first remove the existing, factory installed blank panel at the rear of the Chroma. (The blank panel is attached with screws, a nut and a washer. The nut and washer are quite small — so during removal, be careful not to drop them inside the Chroma).

Figure 11: Removal of Back Panel Blank

Figure 12: Panel Blank Removed

Remove the screws, nuts and washers from the original panel, as these will be used for the installation of the new cable. (The panel itself can be set aside in a safe location, so that it can be reinstalled in the Chroma in future, if desired).

Install a screw, washer and nut loosely in bottom hole of the internal cable bracket and slide the connector into pack panel, having the bottom screw meet with the lower panel — as illustrated in Figure 13. Install the top screw with nut and washer. (Again, be careful not to loose the small nut and washer inside the Chroma). Tighten both top and bottom screws.

Figure 13: Installation of Cable to Rear Panel

From an electrical perspective, the cable screens need to be connected to a 'ground.' There is an existing ground connection near the back connector, as shown in Figure 14.

Figure 14: Location of Pre-Existing Ground

Remove the screw from the existing back-panel ground wire and place the ground-wire from new cable under it. To prevent possible damage to the Chroma, please double-check that the original ground connection was firmly reattached.

Figure 15: Cable Ground Connected to Panel Ground

The location of cable routing is not critical however, it is suggested to pass the cable along the back edge of the Chroma, along the sides and over the dual-stack switch assembly, as shown below.

Figure 16: Internal Cable Routing

Route the cable under the rails, and towards the connectors.

Figure 17: Cable Routing at CC+

Attach the connectors of the cable to the CC+ board. When properly seated, the connectors should 'snap' into place and resist being removed. The cable with the single 6-position connector goes to the bottom left location on the board. The cable with the 6-position connector and the 4-position connector goes to the upper right locations on the board.

Secure the CC+ cabling with tie-wraps (included). There is no 'right' or 'wrong' way to secure the cables - simply ensure that the cables will not interfere with the opening and closing of the panel or the operation of the keys (when the lid is closed). Figure 18 suggests some tie-wrap attachment points.

Figure 18: Suggested Locations to Secure Cable

Installing External Cabling

The external cable has a DB-15 connector at one end to allow attachment to the rear panel of the Chroma and an interface box with MIDI IN/THRU/OUT connectors at the other end to support MIDI connection. The interface box also provides two Light-Emitting Diodes (LEDs), one red and one green. The green LED is used as an external indication of MIDI activity. The red LED is reserved for future use. (Specific connector/LED assignments for the connector are available in the section entitled "MIDI Connector Assignments/LED Assignments").

The external cable has a standard computer-style connector and it can be attached to the Chroma by inserting the DB-15 into the mating rear panel location and then tightening the two screws, as shown below.

Figure 19: Installing External Cable

Checkout of CC+

Proper installation of the CC+ can be confirmed by powering up the unit. Upon applying power, the Chroma should start as per normal (i.e., flashing LEDs to indicate tuning is being performed).

If the Chroma has properly started as per normal, then the CC+ has been properly installed and all the new features outlined in the User's Guide portion of this document should be available.

After booting, the only item which will appear 'different' from an original CPU boot will be that an additional LED should be illuminated in the small LED display, as below:

Figure 20: Extra Decimal Point in DATA READOUT Showing Bank

This LED signifies that the Chroma is currently using patch bank 1.

Note: The CC+ uses signficantly less power than the original Chroma CPU board. Since the electrical environment has changed with the insertion of the CC+, it is recommended as good practice to re-validate the power-supply settings as well as the DAC offset and voice card trim, as discussed in the Calibration and Checkout section of the Service Manual.

Closing the Chroma

To close the Chroma, reverse the earlier sequence of steps which were used to open the unit. Specifically, with power removed, secure the front panel and install the screws for the lid. Once the system has been reassembled, the power cord can be reattached and the installation is complete.

Congratulations on your successful installation!

If any difficulties were encountered, please refer to the Troubleshooting section of the CPU Plus User's Guide.

Additional Information

Default Conditions at Time of Shipping

The CC+ is shipped with programs pre-loaded in all 4 of the new banks. The programs used are ones which are available on the Patch Downloads page. In terms of specifics we have:

The rest of the memory is 'cleared' when shipped, so any specific settings for interfaces such as the Syntech interface will be reset.

The following specific settings will be in place (as shipped):

Programming Interface:

Wiring Diagrams for Internal and External Cables

Internal Wiring Diagram (click for larger view)

External Wiring Diagram (click for larger view)

Errata/Functional Discussions

Any known errata associated with the firmware release can be found on the the Chroma CPU Plus Firmware page.

While the interface is running in expanded MCM mode (P18 = Cust) some MIDI interface parameters change behaviour as follows:

MIDI Connector Assignments/LED Assignments

The drawing below illustrates the port and LED assignments for the external MIDI connector.

Figure 21: Functional Assignments for MIDI Interface Box

Board Outline

Note - the components shown in RED are intentionally not populated on the Rhodes Chroma/Chroma Expander CC+ board.

Appendix (for European customers)

For practical and economical reasons, some of the raw materials and components used to build the European CC+ upgrade kits (serial numbers beginning with EU, made in Italy by Sandro Sfregola) are different from those used to build the North American ones (CA serial numbers, made in Canada by David Clarke).

Most of these differences are practically insignificant for the installer/user; only a couple are really important and are documented here: one of these regards the installation procedure.

Mounting rails

The mounting rails supplied with the EU CC+ are made with C-shaped aluminium profiles; these profiles are very strong and rigid due to their particular structure/shape but they are also thinner in respect to the rails supplied with the CA CC+. For this reason 4 additional plastic washers are supplied: for each rail they must be inserted between the fixing 'standoff' (or screw) and the profile (as the pre-mounted stand-off). Here is the modified portion of the installation procedure:

Installation of the new board is essentially a reversal of the steps above. As the new board is shorter than the original, a set of support rails will be used to allow mounting.

The rails should be installed first. Install the rails with the drawn black arrow pointing to the I/O board (left). Use a provided screw and washer to attach the right hand side of the rails. Use a provided 'standoff' and washer to attach the left end.

Before opening the bag containing the new CPU board, discharge any static which may have accumulated on your body by touching a known grounded item.

Open the antistatic bag and place the CC+ on the rails. Using the screws removed from the original CPU board and the supplied washers, install the CC+ so that the ribbon cables are in the same general orientation as the old CPU board, as shown in Figure 9.

Avoid over-tightening the screws or 'standoff' as this could damage the plastic washers. The next step will be to connect the ribbon connectors from the CPU board to the I/O board.

Cables (MIDI interconnection kit only)

The cables used in the interconnection kit are as follows:

EU kit:

CA kit:

The wire assignments for the Tasker cables are resumed in the following tables:

Internal cables:

Cable #1 (Tasker C12015)

Signal Wire From To
MIDI_RX+ Black J1-1 J4-1
MIDI_RX- Brown J1-2 J4-9
MIDI_THR+ Red J1-3 J4-2
MIDI_THR- Pink J1-4 J4-10
MIDI_OUT+ Yellow J1-5 J4-3
MIDI_OUT- Green J1-6 J4-11
LED+ Blue J2-1 J4-4
LED1 Purple J2-2 J4-12
LED2 Grey J2-3 J4-5
LED_GND White J2-4 J4-13
unused Blue/Red - -
unused Grey/Pink - -

Cable #2 (Tasker C6015)

Signal Wire From To
DISP+ Brown J3-1 J4-6
DISP+ Pink J3-1 J4-6
DISP_TXD Yellow J3-2 J4-14
DISP_BSY Green J3-4 J4-7
DISP_GND Grey J3-5 J4-15
DISP_GND White J3-6 J4-15

External cable/connection box:

Cable #1 (Tasker C12015)

Signal Wire From To
MIDI_RX+ Black J1-1 J2-4
MIDI_RX- Brown J1-9 J2-5
MIDI_THR+ Red J1-2 J3-4
MIDI_THR- Pink J1-10 J3-5
MIDI_OUT+ Yellow J1-3 J4-4
MIDI_OUT- Green J1-11 J4-5
LED+ Blue J1-4 LED1+, LED2+
LED1 Purple J1-12 LED1-
LED2 Grey J1-5 LED2-
unused White    
RP_GND Blue/Red J1-8 J3-2, J4-2, SHLD
unused Grey/Pink    

MIDI connection box (MIDI interconnection kit only)

EU MIDI box use a black plastic lid ("black-face" box) while CA ones use an aluminium lid ("silver-face" box).