DIYPNP Bosch 55 Pin Adapter Board Assembly

Note: This guide applies only to the B55 adapter board included with the early V1.1 boards, which are now discontinued. V1.5 DIYPNPs have the 3 wire IAC driver incorporated into the main board instead, so there is no need for this circuitry with a V1.5 board. DIYPNPs with a V1.5 board ship with a different adapter board that adds spaces to mount two additional coil drivers (sold separately) for those looking to mount six coil drivers inside a DIYPNP. Click here for notes on the newer B55 adapter board.

The Bosch 55 Pin Adapter Board has some extra circuitry for 3 wire IAC control. Here’s how to assemble it. As with the main board assembly, if it’s important not to get a component backwards, we have marked the step with (+/-).

  1. Install all four resistors R1A through R4A in their respective slots.
  2. (+/-)  Install D1A and D2A, making sure to point the banded end to the right.
  3. Install Q3A.
  4. Apply heat sink compound to the silver patch under Q2A. Bolt Q2A into place with a 4-40 screw and solder to the PCB.
  5. Bolt the 55 pin Motronic connector to the board with the M4 screws and solder into place.
  6. Slip the end plate notch into position and put the end plate over the 55 pin connector.
  7. Now for the tricky part – installing Q1A. This one needs both a mica insulator and heat sink compound. Q1A slips into the holes on the PCB and then bolts to the end plate with a 4-40 screw. Then solder it into place.

The 3 wire IAC circuit has five jumpers on a header on the far left of the adapter board. Here is how to connect these jumpers.

  1. The IN jumper connects to the IAC output on the main board.
  2. The OPEN jumper connects to the opening coil wire on the 55 pin connector.
  3. The CLOSE jumper connects to the closing coil wire on the 55 pin connector.
  4. The 12V jumper connects to a 12 volt source on the main board.
  5. The GND circuit connects to any GND jumper on the main board. You must have either the GND jumper in the 5 pin header or at least one of the GND pins in the 2 pin header to the right of the connector grounded for the IAC circuit to function.

Note that you do not need to add any flyback diodes on the main board if using the 3 wire IAC control circuit. It has flyback protection built in.