Building the AKM Converter – Final Revision 05/20/02

http://www.akmcables.com/serial.doc for troubleshooting help

• The printed circuit board is shipped cut to the proper size to have the two DB25 connectors slipped over either end of it.

Parts List:

(8) 10k Resistors, 1/8 Watt

(5) Switching Diodes [1N4148, 1N914, or equivalent]

(5) 1uF, 16V Tantalum Capacitors (preferably tants, but others work too)

(1) .1 uF, 50V Tantalum Capacitor (ditto)

(4) NPN Transistors [2N3904, 2N2222 or equivalent]

(1) MAX232 or equivalent (-ECPE, -CPE, -EPE, -EEPE, -ACPE all work just fine! Or the LTC1383CN chip works great too)

(1) 78L05 voltage regulator, TO-92 Package (looks like a transistor)

Male and Female DB25's

and for a MAF TPI car, (1) more 10k 1/8 watt resistor

• Start by sliding the printed circuit board between the solder cups of the male connector (on the right side in the attached picture). It’s always a tighter fit. I usually slide the cups on the non-metal parts, and then tap the board lightly to make the pads line up with the solder cups. I center the male connector on the pad on Pin 5.
• Next, slide the female DB25 connector on to the board, you may have to tap the edge of the board to line it up. I usually center it on Pin 7.
• At this point, with both DB25’s slipped on the board, solder all of the pads to their respective solder cups. FEMALE is on the LEFT, MALE is on the RIGHT.

• Note that the 7805 voltage regulator (top center of board) is face up, the 4 transistors on the right side of the board are (will be) face down.
• Note the polarity of the 5 diodes. They are all stripe-up, except the one in the top right corner of the board which is flush with the board.
• The second capacitor from the top left is the .1 uF @ 50V unit, all others are 1 uF at 16V. Note the white stripe polarity of the capacitors – the first two the upper pin is (+), the third the upper pin is (-). The fourth and fifth the upper pin is (+), the bottom capacitor the upper pin is (-). Note on these tantalum units the stripe is the (+) leg, and also the (+) leg is longer than the (-) leg. In the kits, I tape the .1 uF/50V cap together with the 7805 Voltage Regulator.
• Next, insert the capacitors (noting orientation above), insert the two diodes next to the 7805, insert the 7805 (bend the legs before you insert it in to the holes), and insert the LTC1383 (or MAX232, they are identical) chip. Use a piece of masking tape to hold all of the components in place, and then turn the board over and solder all of the legs.

• After soldering, cut the legs off of all of the caps, diodes, and voltage regulator. Remove the masking tape and save for use again.
• Insert the transistors in to their holes, and bend the flat sides down as in the picture above. Then place the strip of masking tape over them to hold them in place, flip the board over, and solder them in place. You MUST bend them face down before soldering, otherwise you will break the legs. They must be pushed down as far as they can go – they are rather large bodied, and in order to fit in the converter shell, they must go down pretty far.
• Deflux if you can. Not a biggie, but it makes for seeing any shorted traces or cold solder joints easier.

• If you have a desktop, you can test the converter at this point with Hyperterminal. Connect the RS232 cable to the computer and to the converter, open up a new Hyperterminal session, select "Direct to Com1" (or your appropriate port), set your baud rate to 9600, 8, n, and 1, and Xon/Xoff for handshaking. At this point, anything you type on the keyboard should be repeated on the screen if the converter is working properly. Warning, though, this only works about 80-90% of the time – there are times when the converter is fine and Hyperterminal doesn’t work right – weird! ;)
• Declare it good, put it in its black shell, be sure you put the little holder screws and barrel nuts around the converter, and tighten it up.
• You’re now ready to build the OBD connector portion for the gray hood. You’ll use the female DB25, gray hood, and either wire or if you purchased one of the connectors, you’ll use that.
• On the DB25, I use Pin 1 as Serial Ground ("A" on an OBDI connector, Pin 5 on an OBDII connector – usually a black wire on the AutoXray connector)
• On the DB25, I use Pin 5 as Serial Data ("M" and/or "E" on the OBDI connector, Pin 9 on an OBDII connector – usually a orange wire on the AutoXray connector)
• Only if connecting to a MAF [86-89] based Tuned Port (TPI) car: you need the "B" pin as well. This is a red wire in the AutoXray connector. I usually connect it to Pin 3 of the DB25, and then put a 10k resistor between Pin 1 (ground) and Pin 3. This allows the ECM to enter 8192 baud mode. Below is a picture of a DB25 end used with a TPI car… Note the resistor, the 3 colored wires, and the cig lighter adapter (white stripe on pin 25, black on 22). Also, if you ever decide to switch ECMs to a '730 (90-92 MAP model), you'll need to snip out the resistor.

• On the DB25, I use Pin 22 as Power Ground (the non-stripe wire for a cigarette lighter adapter, or Pin 4 on an OBDII connector) - this is optional
• On the DB25, I use Pin 25 as Power Input (the stripe wire for a cigarette lighter adapter, or Pin 16 on an OBDII connector) - this is optional
• Be sure to install the strain relief for the gray hood. For a single wire connection, I put it together like this )o) and then clamp the heck out of it with the screws. Makes it very tight, and the wires do not slip. It then rests inside the gray hood in its little retainer area. If clamping on the cig lighter adapter wire as well, I recommend taping the two wires (ALDL and cig cord) with electrical tape first to hold them together, and then clamp them like this (o) - that will still be tight enough.
• If building a HPP plug cable,
• DB25 Pin 1 ties to DB15 Pin 1 (I use WHITE wire)
• DB25 Pin 5 ties to DB15 Pin 12 (I use GREEN wire)
• DB25 Pin 25 ties to DB15 Pin 2 (I use RED wire)
• Note that if building an HPP plug cable, you can bring power through the plug if you have an OBDII type interface. If you have an OBDI type interface (1994 and earlier F-cars), you may need to use a cigarette lighter adapter.
• If building a raw converter, DB25 Pin 1 is Ground ("A" or OBDII-5), DB25 Pin 5 is Data ("M" or OBDII-9), and Power is DB25 Pin 25 (OBDII-16 or Cig Lighter circuit).

• To build the OBDII crimp style interface, I use the following wire colors:

• For crimping the pins, I use a normal, plain old pair of pliers (the kind with the slipjoint in the hinge). I strip about ½" of wire, insert the pin at about a 45 degree angle in to the jaws of the pliers, only gripping one side of the pin (only crimping one side of the U shaped channel), give it a slight squeeze before inserting the wire, then roll the pin slightly to get a better grip on it, then insert the wire, and crimp that first side. Then I roll the pin slightly and squeeze on the other side of the U shaped channel. This method has proven most effective for me. J Watch the width of your crimped pins. They need to be as narrow as possible in order to slip in to the connector. Give them another squeeze if they’re not as narrow as the rest of the body of the pin.
• I then solder the wire in to the pin (don’t use too much!), and then put heat shrink that covers about the back 1/8" of the pin (just far enough forward to where the heat shrink dips in to the depression that’s about 1/8" from the wire end of the pin). Any further forward and you won’t be able to insert the pin in to the connector.
• I also put a piece of heat shrink over the piece where the cable sleeve meets the 4 wires when they’re splitting out. Not necessary, but it makes it look better.
• For pushing the pins in to the connector, I use a pair of pointy nosed tweezers, but a very small screwdriver works just as well. Just slip in under the wire, grab the edge of the pin on the side with the tip of your push tool, and push until you feel it "click". Pins 4 and 5 (upper center) will protrude slightly further in to the connector than pins 9 and 16 (lower outer edges).

Want some pictures of the completed cables? Here's some cables that are laying around tonight, I'll try and get a crimp and HPP style cables up here soon. J

First, the OBDI style:

Now, OBDII Style:

And a MAF TPI cord with the Cig Lighter Adapter attached: