The XAP1541 cable combo

Important notes

• You definitely need BSV52 transistors and 4.7 kOhm resistors for this cable, different parts may make the cable inoperable.
• Because you will solder a cable onto some pins of the VIA#1 chip inside the drive, you will have to first make sure that these pins are not used for any other purpose. This depends on the version of the drive you have:
  • In original Commodore 1541 drives, nothing is defined to any of the bits of Port A. You can solder the cable without any problem.
  • In 1541C drives, bit 0 of Port A is used for the detection of the head being over track 1. After stripping this connection off of the chip, you will have to replace the DOS ROM with that of the 1541 or the 1541-II. Otherwise you'll get strange results when the drive is seeking: the DOS tries to rely on the detector line which doesn't exist anymore.
  • In 1541-II drives, bit 0 of Port A is grounded, strip this connection off of the chip.

Construction

First, create the parallel port for 1541 drives or the parallel port for 1570 and 1571 drives.

You need the following parts to build this cable:

• One solderable 6-pin male DIN plug (Commodore serial plug)
• One solderable 15-pin male plug (PC game plug)
• One solderable 25-pin male plug (PC parallel plug)
• Four BSV52 transistors
• Four SMD 1206-style 4.7 kOhm resistors
• A shielded 4-wire or unshielded 5-wire cable of, preferably at most, 2 meters
• A shielded or unshielded 8-wire cable of, preferably at most, 2 meters

Step 1. Solder one end of the 5-wire cable onto the DIN plug.

Step 2. Solder those wires of the 5-wire cable, that don't go through an enhancer, on the other end of the cable onto the parallel plug. These include the following connections:

Step 3. Build the enhancer bridges, consisting of one transistor and one resistor each, between the appropriate pins of the parallel plug. These include the following connections:

The collector of the transistor should be pointing towards the pins in the left column of the table. The base of the transistor should be pointing towards the pins in the right column of the table; this is also the place for the resistor. The emitter of the transistor should be grounded.

Step 4. Solder one end of the 8-wire cable onto the game plug.

Step 5. Solder the other end of the 8-wire cable onto the parallel plug. You should have the following connections:

Circuit diagram:

You can find the description of all parts used on the diagrams at the legend page.

Source: The Joe Forster-STA homepage

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