The XTB has a densely populated circuit board. Assembly requires experience working with small components, and the ability to correctly identify component values.  A low-wattage soldering iron with a 1/8" or smaller tip is recommended.  Care must be taken to properly align the tiny surface-mount op-amp before soldering, and the semiconductor devices should not be overheated.  Several components have been packaged separately because identification can be difficult.  Please be careful not to mix components from the different packages together.

BEFORE ASSEMBLY

DO NOT MIX UP THE COMPONENTS.  A few people have had trouble identifying some of the components.  Several components have been packaged with the semiconductors to help identify them.  Those include the two tiny Pico fuses and zener diode D9.  It is best to keep them packaged until you are ready to install them.  If you have trouble identifying any components, please refer to the detailed parts list with physical descriptions at the end of this document.  That will be helpful to those of you who may not be familiar with manufacturer coding or resistor color charts.

PRINTED CIRCUIT BOARD ASSEMBLY:

Please read the Detailed Assembly Instructions below before beginning actual assembly.

XTB Rev 1.1 was renamed the “X10 Transmit Booster” because it not only buffers X10 transmissions, but it also boosts their output power.  Two tiny Pico fuses were added to the XTB Rev 1.1 board to allow the fuse limit to be matched to the application.  Additional pads were also added at C6 to make it easy to install capacitors with either 0.1 or 0.2 lead spacing.  Since none of the changes between Rev 1.0 and Rev 1.1 significantly affect the assembly process, the photographs for Rev 1.0 have not been updated.  Both versions of the layout are available.  Please refer to the one that matches the printed circuit board included in your kit:
 
Printed Circuit Rev 1.0 Layout Diagram.
Printed Circuit Rev 1.1 Layout Diagram.

Do not try to assemble the XTB with a high wattage soldering iron having a tip larger than 1/8".  I use a variable temperature iron with a 1/16" tip.  After assembling over 100 XTBs myself, I recommend installing components in the following groups:

D10, D11, D12, D13
D1, D2, D9 (D9 is from the semiconductor pack)
R2, R9, R15
C3, C9, C6
R6, R5, R14, R4, R16
U1
D4, D3, D7, D8 (Only D8 band down, others band up)
R13, R12, R3
R10, R11, D5, D6 (Only D6 band down)
C7 (bar or + sign near D5)
C1, C2, C4, C5, MOV
R1, R8
F1, F2 (from the semiconductor pack)
L1, L2
L3, L4 (skinny end up)
Q1, Q2
Q3 (metal tab toward board edge)
R7
C8 (check polarity)
Transformer (2-pin primary near C4 / C5)
LED (long pin at +)

DETAILED ASSEMBLY INSTRUCTIONS:

Many components stand on end in order to fit into the available space.  This should make it easier for the DIY builder to assemble the XTB than if it had used smaller surface-mount devices.  The size of the board is determined by several major components that are not available in surface mount packages anyway.  Be careful when installing diodes because the banded end must be at the pad labeled "K" in the layout diagram accessed by clicking the link above.  The "K" does not appear on the silkscreen, but that pad will have an extra circle around it for identification.  Most of the diodes mount banded end up, but D6 and D8 mount banded end down.  You can verify correct diode polarity by comparing with those installed in this photograph if unsure.

Install the smaller devices that are flush to the circuit board first.  Use caution not to accidentally mix up zener diode D9 with one of the 1N4148 diodes.  They are the same color, and almost the same size.  The zener is very slightly larger, and is packaged with the last group of semiconductors to be installed.  If these do get mixed up, it takes a strong magnifier to read the part numbers on these tiny devices.  Work your way up to the larger passive components.  The small ceramic capacitors may vary in size and color depending on the manufacturer.  Be certain that the 0.22uF is installed at C3.  Also be careful not to confuse the Pico fuses with the resistors.  They are similar in size, and magnifier may be needed to read the current ratings.  The Pico fuses are packaged with the semiconductors to make identification easier.  They may look identical to each other, but they have different current ratings.  Be careful to install them in the correct locations.  The higher current fuse should be installed at F1.  There are extra pads for some of the capacitors to accept alternate devices with different lead spacing.  When supplying your own components, please verify alternate devices will fit into the space available before ordering.  Be sure you install the two polarized capacitors correctly.  The little tantalum C7 is installed with the bar or + sign to the right near D5.

The op-amp should be installed near the end to reduce the chance of static damage, but it is easier to install before the other passive components that surround it.  The op-amp is located with pin 1 (tiny dot) near D8.  A technique that works for me is to carefully position it over the pads and hold it in position while just touching the tinned iron to one corner pin.  If alignment isn't perfect, that pin can be reheated and the position adjusted slightly until the pins are centered on the pads.  Then using just a quick touch, solder the pins using the barest amount of solder to avoid bridging the connections.  Be very careful not to overheat.  When you are done, check the quality of these connections with a magnifier.  This is certainly the most delicate operation of the entire assembly.  The op-amp is available in DIP and T05 versions, but there was just no way to squeeze these larger devices into the space available.  Install the transistors and power FET near the end because of their sensitivity to static damage.  Be sure to orient the transistors and FET to match the marking on the silkscreen layer.

The transformer should go on next to last because of its size and weight, followed by the LED.  The transformer can have 6 or 8 pins.  CAUTION:  The primary winding (2-pin side of a 6-pin transformer) is positioned near C4.  In either case, transformer pin 1 goes into the hole with the square pad near the MOV.  The transformer may be a tight fit, and should be pressed firmly down onto the printed circuit board until its plastic base is seated.  Be careful not to flex the printed circuit board during this process so there is no danger of damaging other components.

The LED is mounted full-length with sleeving over both pins.  The parts kit should contain a 2" length of clear sleeving.  Cut that exactly in half and trim slightly so the shortest lead extends just through the circuit board.  The longest lead goes into the + pad.  If the cover isn't pre-drilled, drill a matching hole in the cover 1/2" up from the bottom, and 5/8" in from the side.   A 3/16" hole will keep the LED recessed inside the cover, and a slightly larger hole will allow the LED to pop through.  When the cover is installed, the LED should be angled to face up into that hole.

INTERWIRING & FINAL ASSEMBLY:

IMPORTANT:  The Polycase base must be modified to prevent conflict between the XTB circuit board and the internal extension of the AC plug ground pin.  That extension will be removed from bases shipped with XTB kits.  If your base has not been modified, use a rotary tool with a small cutoff disc to remove the internal extension of the ground pin so that it is flush with the plastic base.  It was impossible to create a layout that provided enough clearance so the ground pin extension did not have to be removed.  I don't know why Polycase did this, as it is clearly not required for any mechanical purpose.  An alternate approach is to mount the board using 4 short insulated standoffs, and longer screws.

The AC receptacle should be pressed into the opening in the Polycase cover with the same alignment as the plug on the base.  The receptacle doesn't lock in securely unless a screwdriver is used to force the plastic tabs slightly outward until they click into place.

Six connections go to the AC sockets.  The 8" green wire supplied with the kit will run directly between the ground pin on the plug and the ground pin on the socket.  While not necessary for proper operation, this connection should be installed for safety.  Insulate the plug ground tab with shrink sleeving to keep it isolated from the printed circuit board.  The parts kit will include short pieces of 1/8 and 3/16 shrink sleeving to double insulate the ground tab.  Keeping the ground tab flush with the plastic base, the ground wire should be looped back on the left side of the case, and around the left plug pin on the way to the top cover.  Be careful not to melt its insulation when later soldering that pin.

The remaining wire should be cut into 4 pieces:  3", 6", 6", & 7".  Strip 1/8" from one end, and 1/4" from the other end of each of these wires.  Tin both ends.  The short end of each wire is soldered to the printed circuit board as follows:

        3" at the right COM hole near the large capacitor ground lead
        6" at the left COM hole near the large capacitor ground lead
        6" at AC hole near L1
        7" at X10 hole near L2

Make sure all leads are cut very close to the circuit board, especially in the area around Q2 to provide maximum clearance for the ground tab when the printed circuit board is mounted.  The board mounts to the base with 4 screws.  The double insulated portion of the ground lead will be compressed slightly when board is mounted, but that portion of the circuit board contains no solder connections.  Make sure the ground lead itself is routed off to the side, and that no solder connections along its path have sharp points that could pierce the insulation.  If you wiggle the ground lead slightly as the board is fastened down, it should position itself between points of compression.  The wire included with the kit is rated 600V, and most active circuitry is operating near ground potential when properly wired.

After the board is mounted, the AC connections are made as follows:

Check the AC & X10 connections because the XTB will not work if they are reversed.  Carefully push excess wire going to the AC connectors into the free space inside the cover, and mount the cover with the LED angled to be visible through the hole.  Add the 24-watt warning label to the cover just above the receptacle, and the XTB label to the recessed portion on the back.   Just email me your address if you would like a label for one of the early units that were shipped before the labels were created.

TEST & OPERATION:

As a final check before applying power, verify the resistance between the two plug prongs is about 160 ohms.  If it reads much lower, the transformer may have been installed backwards.

Once assembled, plug it into an AC outlet with a manual X10 controller plugged into the receptacle for testing.  The LED should only flicker when the XTB is amplifying an outgoing X10 signal.  The LED will not be illuminated all the time like the one on the TW523/PSC05.  If the LED is ever illuminated constantly, please unplug the XTB immediately.  That means a fault condition exists that must be resolved.  It might occur if the XTB is plugged into a receptacle without a X10 transmitter connected.  If the LED does not flicker at all, then it is likely something is wired wrong.

The X10 input receptacle will supply 24 watts maximum.  That is about 10 times the average current drawn by a typical X10 controller.  The Rev 1.0 printed circuit board contains a fine trace for F1 near the large pad labeled AC.  That trace has been sized to handle the high-current X10 signal, but will pop if there is a major overload or electrical fault in the XTB.  Inductor L1 or L2 in Rev 1.0 may open circuit if the 24-watt limit is exceeded for a period of time.  Rev 1.1 contains a Pico fuse (F2) between L1 and L2 that will pop if the 24-watt limit is exceeded by even a small amount.  That should never happen when the XTB is used for its intended purpose.  Obviously, the cause of the fault should be found if either the trace or one of the fuses must be replaced.  While not recommended, a popped Pico fuse could be replaced by a single fine strand of wire from a length #18 flexible lamp cord.  To offer protection, that #18 lamp cord should have at least 40 fine strands of wire.  Form that into a loop away from the printed circuit board before soldering.  X10 modules use a similar inexpensive wire loop for protection.

REV 1.1 & CONVERSION TO 240V OPERATION:

Several changes were incorporated into the XTB Rev 1.1 printed circuit board to make conversion to 240V more feasible.  Version 1.0 accepted a dual-primary transformer, but included default traces for 120V operation.  Those default traces had to be removed for 240V operation.  Rev 1.1 does not include the default traces.  Two jumpers must be installed as shown on the silkscreen to use a dual-primary transformer on 120V.  A single jumper must be installed as indicated on the silkscreen to configure a dual-primary transformer for 240V operation.  As in Rev 1.0, additional pads around the transformer make it possible to use transformers with different secondary voltages.  No jumpers are necessary when using the standard transformer with dual 6.3V secondaries.

Operation on 240V requires several capacitors to be changed to higher voltage units.  They are physically larger, and several components in the high-voltage section were repositioned slightly to provide as much room as possible.  While still very tight, those larger components can now be squeezed in.  In addition, the thin printed circuit trace used as a fusible link in Rev 1.0 has been replaced by two Pico fuses in Rev 1.1.  This allows the board to be fused at a lower current for 240V operation.  The downside of converting to Pico fuses is that even a brief overload in excess of the 24-watt limit will likely pop one of the fuses.  So you must be careful never to exceed the 24-watt rating on the X10 receptacle.

One issue that must still be addressed for 240V operation is the power connector.  The XTB was designed for the North American market, and incorporates the corresponding 120V plug and receptacle.  Some means of converting to your local 240V connectors must be addressed when converting the XTB for 240V operation.  While 240V operation should be feasible after all necessary modifications, that mode of operation is currently being evaluated.

Please contact me if you have any questions at: JeffVolp@att.net
If you don't receive a response within 24 hours, try: JeffVolp@beyondbb.com