WBo2 2A0 Construction Guide

(22 October '04) -- These notes should help you construct your own TE WBo2 (2A0) Bosch LSU4 / NTK L1H1 oxygen sensor interface unit. As noted in the location guide, there is a rev-2, rev-3 and now Rev-4 PCB with only small differences you need to be aware of. For the rev-4 PCB, the major change is removal of some jumpers, and the addition of the NTK jumper, which should be ON for the LSU version and OFF for the NTK version (yes, it should be called the LSU jumper). For the rev-3 PCB the NTK version has a small resistor difference that is noted below. Please read all text before you start as many procedures should be perform in sequence. Many of the images below can be enlarged by clicking on them.

Firstly inspect your bare PCB for any shorts between adjacent tracks. We normally have very few problems of this nature, but we'll sometimes get a batch of PCBs (from a single panel) that have been under-etched, resulting in an odd hairline short. It's best to find any board faults before you've built the unit because the IC sockets often make it difficult to find shorts afterwards.

Modifications Required to the rev-2 PCB

You should find one trace that has been removed (on the 2A0 rev-2 PCB, not the rev-3 PCB), this is shown in the image at left as the RED trace. Note also that the PCB comes with the DAC7612 device already soldered in as some may find the SOIC-8 (8 pin) difficult to mount correctly.

If you haven't already done so, you should go here and print off component location image(s).

The silkscreen has visual cues for using 1% or 5% resistors. The 1% resistors having a dotted line as shown in the blowup at right. 5% Resistors are also marked in Yellow on the Color Component Overlay, While 1% Resistors are marked as Green

It is important that 5% resistors are not used where a 1% resistors is called for. But it's okay to use a 1% in place of a 5%. We may actually substitute a 5% with 1% in the parts kit from time to time, but we will never substitute a 1% with a 5%.

Note 1 : all the 100 ohm resistor can be substituted with 5% resistors without loss of accuracy - the overlay shows these as 1% items on the rev-2 and rev-3 PCB.

First we insert the physically lowest components - these are the resistors, and we have inserted just the 5% resistors first as these are more numerous. The 5% resistors will all have just 4 coloured bands with an extra gold band indicating the 5% tolerance. 5% resistors typically have a beige or light brown background. It's best to orient them with the gold band to the right and to the top so the values can be most easily read from left to right and bottom to top as the silkscreen is printed.

Next the 1% resistors go in. Note that the three 0.22 ohms resistors (top mid right, very light blue) may be supplied as either 2% with a red band rather than brown (most likely), or in some instances, as a 5% (with standard gold band).

Note 1 : R214 is 82 k for the NTK version but 910 ohms for the LSU version. It is very important that the correct resistor is used, particularly for the NTK version as the sensor can be damaged if the 910 ohm resistor is used. Note also that the NTK or LSU versions requires the correct firmware version for correct operation. Lastly, (as noted below too) the header shunts should now always be placed in the LSU position.

Note 2 : Despite the images and silkscreen showing all the 100 ohms resistors as being 1%, there are only two (R204, R205) that should be 1%, and even then there's no problem using 5%, so don't worry if all 100 ohms are 5% (or if they are all 1%).

The image shows resistor R2 (10 Ohms 1 Watt) mounted vertically as it will not fit easily horizontally. In practice, it may be easier to put R2 in as one of the last operations as this will aid assembling more of the components that sit low to the PCB.

Note : R401 (= 15k 1W) is the large resistor outline in the lower left corner (marked with "cyclist" symbol on Rev-2 PCBs).

At this stage we should have all the 1% and 5% 1/4 watt resistors in place. We can now put in the capacitors and diodes as described below.

Capacitors come in a few different forms, and it is important to use the correct ones. Typically block monolithic, ceramic, and polyester capacitors are not polarized, This means you may insert them either way around.

Electrolytic capacitors (see image at left) are polarized, and must be inserted with the negative pin (usually marked with a white stripe, and a negative symbol) closest to the 'stripe' on the component overlay.

The image at right (rev-2 PCB) shows two extra 100 nF (104) capacitors (SNUB1 & SNUB2) that must be added to the bottom of the PCB. They both solder to the centre TO220 pad. The rev-3 PCB has holes for these capacitors but they are still located under the PCB.

Note that (for the rev-2 PCB) C212, C7B & C306B are not installed on the PCB.

Diodes

Diodes are also polarised. Most are installed vertically on the PCB as shown in the image at right, with the diode's band closest to the PCB circle.

Make sure you install the 1N4746A zener diode (D403, shown as "03" on the overlay) in the correct position as it is easily confused with the 1N4148 (slightly smaller) diodes alongside.

The 1N5822 (D1) Schottky Diode & 1N6832 1.5KE-33A (D2) Tranzorb are installed horizontally with their band matching the stripe marked on the component overlay. Ensure that they are in the correct position before applying power else damage to the diodes and/or the PCB may result.

Install the 16 MHz Crystal (X1). It may help to install the 28 pin socket at the same time as they will then both be a better fit. Install the 2 Inductors (L1) & (L2) vertically as shown.

Place the TO-220 (7805 and MTP3055V) packages into the PCB from the top, and bend their legs over 90 degrees so they lay flat on the PCB. Bolt the TO-220's to the PCB using the supplied M3 screws, star washers, and nuts, and lastly solder them into the PCB. Note : no insulator washers or thermal transfer compound is required, as very little power is dissipated by the switchmode heater circuit and low current 5 Volt supply.

LEDs and IC Sockets

Now the LEDs are installed (although it has been suggested this should be the last step before switching on). The image shows the position of each coloured LED and also the flat at the base of each LED which must be oriented away from PCB's edge. Note that the bottom surface of each LED should be 17 mm from the surface of the PCB (see the next image at left) so they just protrude through the pre-drilled holes in the case's lid. One way to get the LED clearance just right is to use a piece of soft, but rigid card (height = 17 mm) as a temporary spacer under the LED while it is soldered.

The LED's legs may need to be bent a little so they align with the pre-drilled holes in the case. If you made the legs a little longer, then they can be reduced in height by kinking the legs a little, rather than the more drastic resoldering.

Lastly, put in the IC sockets noting that their pin 1 indent is correct (to the left or top).

At right is an image of the completed unit but without the ICs inserted. Click on the image for an enlargement.

As noted above, the image at left, taken from the PCB area under the fuse, was intended to show how the jumper block or shunts, should be placed on the header strips. However, the design was changed and the LSU only position should now be used.

J4 should be in the 1-2 position for 12 Volt (or COIL) operation, but for lower voltage (RPM from ECU) operation J4 is in the 2-3 (rev-3 and up PCB) or 4-5 position (rev-2 PCB only) .

Insert the 6 gold test point pins into the PCB at the points marked as TEST 1, 2, 6, 5 (near centre of PCB) & TP3, TP4 (top left). Note, the pins have a shorter thick end and a longer thin end. The thin end should be inserted into the PCB from the top (it may still be a tight fit - do not force the pin, check you have the right end). Solder and then cut off the long protruding pin on the solder side of the board.

For the two fuse holder clips, insert into the PCB and solder, taking note the little tab that locates the fuse are installed to the outer sides. You should check before soldering by inserting the fuse, but remove before soldering though.

At the left of the PCB, install the flat green 8 pin connector (Y2 for the logger) so it rests on the top side of the PCB. Note : remove the mating connector with the screw terminals before soldering.

At the other end of the PCB, snap the RJ45 socket Y1 into the mounting holes on the PCB, ensure it's sitting flush with the PCB, and solder it in place.

The clear bodied 2 pin right angled Molex power connector is installed in Y4 so it sits flush with the PCB (as there is no locating tab for it, make sure it is square before soldering).

Step 1 - Special attention to the mounting of the 8 pin circular connector is required. The connector must FIRST be attached to the black endplate, using the large hex nut and spring washer. Note the end plate has a locating flat for the connector. You must secure the connector before the small PCB is soldered to the 8 pin connector. The hex nut cannot be attached or removed without damage afterwards. This is shown in the image at left, note the spring washer is under the hex nut. Firmly secure the hex nut, but don't twist the housing nor damage the connector's threads.

This shows the construction of the RJ45 to DB9 cable - used for serial comms to PC (or Palm etc.). The RJ45 comes pre-crimped, but check the colours carefully (the locating tab is under the wires in the image).

At the DB9 end, a cable tie should be used to secure the cable (drill two small holes in the grey backshell).

Note how the cable "crosses over" between pins 2 and 3 between connectors.