OSA Link Cable

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OSA-Link Cable Clone

(Durchführung auf eigene Gefahr, keine Ansprüche auf Schadensersatz)

The SciSys Leonardo and Saitek Galileo and Renaissance chess computers could be connected to a PC via an OSA-Link cable. Such a cable is needed to run the OSA-4-Arena software and other tools. Unfortunately that cable is no longer available.

 OSA-cable information

It was connected to a special serial interface with TTL level (0-5V) under the board as 5-pin-connector:

OSA Link.png

Several versions of communication cables were available for different computers, like the IBM PC:

Saitek Adapter III.png

Special information can be found in the manual 'Connection Cable for Leonardo Chess Computer', published from Saitek in 1987. It is available as download at www.zanchetta.net/echecs, look under Documentations and Saitek. The pictures above are taken from this specification.

The PC side of the cable has a RS232 (±12V) serial interface. A small box between the interfaces contains a TTL-RS232 converter.

Osa cable 3.jpg

On the PC side (right) only GNG, RxD and TxD are connected. The OSA interface (left) has GND, RxD, TxD, 5V (regulated) and 9V (unregulated). Both voltages are needed by the TTL-RS232 converter MC1488P. The IC on the left (yellow circle) is a regulator for the 9V from the OSA interface. The next picture shows the original circuit diagram.

Osa cable 4.png

 Possible replacements

Is is relative easy to re-assemble an OSA-cable. You will need a modern IC for the TTL-RS232 conversion and two cables, one with a 5-pin-DIN male jack and the other with a 9-pin female RS232 socket.

As IC you can take the well known MAX 232 or an ADM232L. Both ICs need only 5V to operate, so the 9V from the board is not needed and will make the work easier.

The next pictures show the principle circuits for both ICs.

Osa cable 5.png Osa cable 6.png

For the ADM232L you will need 5 condensers with 1 μF each, that's all. The IC has two communication lines (T1/R1 and T2/R2), for OSA only one will be used.

Osa cable 7.png

The MAX232 is very similar.

You can choose any of these ICs and assemble your own circuit, but it will be much easier to buy a ready-to-go assembly kit. A fellow at www.schachcomputer.info found a very nice kit at www.pollin.de, a german electronic distributor. It is still possible to order the kit from foreign countries.

 TTL-RS232 adapter from Pollin

The german company Pollin offers a complete assembly kit for the TT-RS232 conversion. It is small, easy to build and cheap.

Osa cable 8.jpg

You can order via internet at www.pollin.de:

Order-No. Article Price EUR (2009)
810036 Bausatz RS232-TTL-Wandler 3,95
720738 Sub-D-Verlängerungskabel, 9-pol., 1,8 m 1,25
560172 Audiokabel, 2x DIN-Stecker 5-pol., 1,5 m 1,95

The Sub-D cable is for the connection from the adapter to the PCs serial interface and optional, if you don't have one. If your PC or Laptop does not have a serial interface, you can use an USB-to-RS232-adapter (not available at Pollin). The 5-pol.-DIN cable is for the connection to your chess computer. One of the plugs will be cut off and the single cables will be plugged into the clamp of the Pollin adapter.


You will get the following parts from pollin for the TTL-RS232 adapter:

Osa cable 9.jpg

The connectors for the TTL-cable and the RS232 jack are self-descriptive. At the bottom of the picture you see a condenser of 100 nF (C5), the fitting direction doesn't matter.

The IC (MAX232) should be fit with the notch at one end into the corresponding place on the circuit board:

Osa cable 10.jpg

The condensers on the left with 10 μF have a plus/minus orientation. It is important to fit them in the right orientation to the circuit. Plus is marked on the board with a + and minus with a bold-white line (see C1 to C4). The condensers are marked with a coloured line and the number 0 in it for the minus pole.

Osa cable 11.jpg

The next picture shows the printout of the circuit board with the position of all parts.

Osa cable 12.png

After assembling the circuit and careful soldering of all contacts the item should look as follows:

Osa cable 13.jpg

The PC side is now still ready and you can connect a 9-pol-Sub-D cable to the left. For the chess board side only the above four connections are needed (5V, GNG/Masse, TxD, RxD).

Take the 5-pol-DIN cable, cut off one plug and strip the wires. Then check which wire (different colour) is connected with what pin at the DIN-plug. Check that the plug is in the correct orientation with the OSA-plug layout.

Osa cable 14.jpg

Use a measurement device to find out the cable connection and write it down.

Osa cable 15.jpg

The 5-pol-DIN cable from Pollin has the following connections:

Pin-No. Description Colour
1 TxD blue
2 GND yellow
3 Rxd red
5 5V white

The wire to pin 4 is not used and can be cut off. The colours may vary from manufacturer to manufacturer, even if you buy it from the same vendor. So please check the cable connections carefully!

To fit the wired into the plugs of the circuit board it is a good idea to fold the ends. This will give a more stable connection in the screwed plugs. Do not tin-plate the wires with solder, just use the copper wires as they are.

Now you can fit the wires into the plugs of the circuit board.

Osa cable 16.jpg

Fit 5V (white) into the right plug and GND (yellow) in the second plug. RxD (red) shall be fit into the TxD-plug and TxD (blue) shall be fit into the 4th plug (RxD) of the circuit board.

That's all, now you have your own OSA-Link cable and can use all of the available software for your chess computer. Have fun!