This guide provides instructions for converting a non-VTEC "1720" board to support VTEC operation.

Required Components#

To enable VTEC on a non-VTEC "1720" board, the following components must be installed:

• Q26: C27850 NPN switching transistor (or a C144 as a verified alternative).
• C60: 1uF 35V tantalum capacitor (marked "1... 35" with a blue polarity mark).
• IC14: 515X High Side Switch0.
• J10: Jumper wire.
• R67: 820 Ohm, 1/8W 5% resistor (1k resistor is also acceptable).
• RM11: Voltage divider module (can be substituted with a 10k 8-pin resistor module).
• D11: Clamping Diode0.

Optional Components#

The following components are largely considered unnecessary for the conversion:

• C75, C89, C72, C74, C88: 22pF ceramic capacitors (marked "22").
• IC13: 515X High Side Switch0.

Technical Notes#

This board design is one of Honda's early OBD10 efforts. It is more complex than necessary.

Regarding IC13: The IC13 component is entirely superfluous. It is recommended to remove it and install a jumper wire at J10 to bypass it. IC13 and IC14 are run in series, meaning installing both significantly increases the probability of failure.

Component Locations#

• C60 & J10: Top left of the ECU case.
• RM11: Resistor setup.
• Q26: NPN Transistor location.
• IC14 & R67: 5151S driver and resistor.
• D11: Diode located in the upper left of the case.