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Chipping the JDM OBD1 P30 ECU

Hardware modification guide for socketing, chipping, and converting JDM square-case OBD1 P30 ECUs to manual transmission.

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Adapted from pgmfi.org wiki

The Japanese Domestic Market (JDM) OBD1 P30 DOHC VTEC ECU is housed in a compact, square-shaped metal casing, which differs from the larger rectangular casing used for USDM ECUs.

Because of the compact board layout, chipping a JDM P30 requires working with surface-mount devices (SMD) rather than through-hole components. The memory latch (74HC373) must be soldered directly to SMT pads on the board.

1. Required Components

To chip a JDM P30 ECU, source the following components:

Component Location Description / Value Manufacturer / Part Number
Latch (IC) 74HC373 SMD Latch (SOP-20 package) SN74HC373NSR (Digi-Key: 296-8310-1-ND)
ROM Socket 28-pin low-profile DIP Socket Standard 0.6" width DIP-28
EPROM Reprogrammable EPROM SST 27SF256 or 29C256
C49 & C50 0.004 uF SMD ceramic capacitor Digi-Key: 399-1230-1-ND
C91 & C92 0.0001 uF (100 pF) SMD ceramic capacitor Digi-Key: 399-1192-1-ND

Warning: The original reference images showing the precise locations of the capacitors and jumpers on the board underside were not recovered from the legacy archives. Ensure you verify the pad labels silk-screened on your PCB before soldering.

2. Step-by-Step Chipping Procedure

  1. Install the SMD Latch: Locate the footprint for the 74HC373 latch on the board. Apply flux to the SMT pads, align the chip pins (ensuring the pin 1 notch matches the board layout), and solder the SOP-20 chip in place. Check for solder bridges between pins.
  2. Solder the ROM Socket: Clean the factory solder out of the DIP-28 through-holes on the board. Insert the 28-pin socket from the top side and solder all 28 pins from the underside.
  3. Add Filtering Capacitors:
    • Solder C49 and C50 to their pads on the underside of the board.
    • Solder C92 to its pads on the underside.
    • Solder C91 to its pads on the top side of the board near the latch.
  4. Bridge Jumper J1: Bridge the pads at jumper J1 on the underside of the board with a blob of solder or a small wire. This tells the internal microcontroller to bypass its internal ROM and read from the newly installed EPROM.
  5. Insert the EPROM: Insert a programmed SST 27SF256 EPROM into the DIP-28 socket. Make sure the notch on the chip matches the notch on the socket.

3. Datalogging & Real-Time Programming (RTP)

If you plan to use a real-time emulator (like Moates Ostrich) or datalog via the serial port using Crome:

  • Remove J4: Locate and desolder the 0-ohm jumper resistor at position J4 on the top side of the board. Removing J4 disconnects the factory debug routines and enables full-duplex serial data transmission.
  • Install CN2 Pins: Solder a 4-pin male pin header (0.1" spacing) into the CN2 port location to connect your USB-to-TTL datalogging cable.

4. Automatic to Manual Transmission Conversion

To convert an automatic JDM P30 ECU to a manual configuration and prevent automatic lockup solenoid CELs:

  1. Locate the resistor array in the bottom right section on the underside of the board.
  2. Desolder and remove resistor RP18 (marked "472" / 4.7k ohms) and replace it with a solid jumper wire (0 ohms).
  3. Desolder and remove resistor RP17 entirely, leaving the pads open.

Credits and source

Authors Speedz, synoptic, coupe-r

Source Adapted from Chipping JDMP30 on pgmfi.org wiki. Licensed under CC BY-NC-SA 1.0.