CDTV Joyport Adapter

After finally getting hold of a Commodore CDTV, first thing I noticed was that it did not have the usual DB-9 connectors that the other Commodore models have. The machine did have a mouse port, but it turns out it is not a standard one, and I did not get one with the machine, so I had to find another solution for using mouse and joystick, because the remote controller was a weak subtitute for a real joystick and mouse in my opinion. I also wanted to use a modern optical mouse together with my already made PS/2 to Amiga adapter.

Looking at the CDTV service manual, at page 17 there is a chip marked 252609-02 at location U75. Turns out it has all the pins for both the joystick port and mouse port. My first plan was to solder wires directly from the chip and onto 9-pin connectors with solder cups. But then I decided to draw a PCB in Eagle CAD instead.

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I opened my CDTV and it turns out there are a few components blocking a big PCB, plus that the distance between the mainboard and the lid is quite narrow. So I had to make the size and placement of the connector as shown above. The idea was to use the same principle they use when they make adapters for EEPROM programmers. There is a socket for the original chip, and then there is legs on the underside to insert into the socket on the motherboard. Now we can just route some traces from the pins on the chip that has the needed signals for left, right, up, down, fire and ground without soldering on the chip itself.

I found out that on Ebay they still had IDC DB9 connectors that was perfect for his project. Turns out 20 pins IDC sockets were much cheaper than 18 pin, so I decided to design the board for a 20 pin connector, but to only connect 18 pins (2pcs 9pin connectors) So the board consist of these parts:

1PCB, 1pcs 20pin IDC, 2pcs IDC d-sub 9 pin male, Turned pin header for inserting into the U75 socket, 1pc 40pin DIP socket for the 252609-02 chip, Double 2.54mm header for the 20pin IDC, 45-50cm IDC cable.

It turned out that the distance between the lid and the PCB was so narrow, that I had to use angled pin headers for the 20pin IDC connector. Below, in the picture to the right, you can see that the connector take a lot of room, so I had to desolder the pin header and replace it with one with angled pins as shown on the left picture.

 

Because the CDTV remote uses the pins from Joystick port 1, there might be a problem using both at the same time with a mouse or joystick. The solution is to try and press RIGHT on the CDTV remote once the CDTV is switched on with your program or game loaded. If this wont work, you can disable the CDTV remote like this: remove U75, bend up pins 6, 7, 8, and 9, and replace it back in the adaptor’s socket. I might make a jumper or DIP switch solution on my next revision of the PCB, so that those pins can be disabled without disturbing the chip. They will fit perfectly on the side of the 20 pin IDC connector. If you look closely on the picture, you will se that the pins are bent to the side. I dont recommend anyone to bend them several times. A different approach to solve this would be to cut the traces on the adapter instead, to avoid bending the pins. The traces to cut would be the ones leading from the socket on top of the adapter that lead out from the 4 pins I bent in the picture.

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This project with PCB and parts can be purchased on ebay:  https://www.ebay.com/usr/kirsti_73
or from Sellmyretro.com

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