WARNING:  Modifying X10 hardware as described in this section will void the
warranty of the hardware. Any modifications you do are at your own risk
and the results are entirely your own responsibility. You may end up
damaging the hardware beyond use. Remember, X10 devices are connected
directly to the power line, and can kill you. If you feel uncomfortable
about any of this, don't do it. The modifications in this section have been
tried by one or more people. They may not work for you, due to variation
in technical skill, or variation in X10 equipment lots. Again, you are on
your own; use at your own risk!

Q501. How do I modify appliance modules for momentary operation?

Normally appliance modules turn on and stay on in response to an ON
command, and off in response to an OFF command. In response to an ON
command appliance modules modified as described in this section will pulse
on then off twice, returning to the off position.


        1. Make sure module is off, unplug it and then take cover off.

        2. Locate 330K resistor below the IC chip. Remove it.

        3. Reassemble and test the module.

The module clicks twice because each X10 command is issued twice. Thus the
two commands causes two on/off cycles. If you would like the module to be
normally on, make sure that the module was left on before you start the

Q502. How do I add local dimming capability to wall switch modules?

There are X10 wall switches with local dimming capability, but these are
not as widely available and reasonably priced as the X-10 WS467. This
switch has a local on/off toggle and a slide button to lock it off. The
light it controls can be dimmed only from a remote X10 transmitter.

The difference in circuitry between the switches with and without local
dimming capability is minor. Those with local dimming capability have a
jumper wire where those without local dimming have a resistor and
capacitor. To convert a switch without local dimming to one with local
dimming, you will need to remove the resistor and capacitor and replace
them with a wire. You will need  a jeweler's flat-blade screwdriver, a
soldering iron, and a desoldering bulb or solder-up wick. You may find
needle nose pliers to be helpful as well.


        1. Make sure the switch is functioning properly before starting.

        2. Take the module apart all the way. Using the screwdriver,
press down on the tabs at the four corners of the back cover, and pop the
cover off. Be careful not to break the tabs. Remove the circuit board from
the case by prying the side of the case away from the side of the board
with the screwdriver far enough so that the PCB can clear the tabs which
hold it in place. As the PCB comes out, be careful not to lose the small
metal tab or the tiny spring-loaded rod which form part of the cutoff
switch. Also remove the plastic piece which holds the cutoff switch
assembly in place; removing the switch assembly now will make it easier to
reassemble the switch properly later. The following is a crude ASCII
diagram of the component side of the WS467 PC board, showing relative
locations of various components.

 |                                 |          TRIAC
 |                                 |            /
 |                                 |          /
 |                                 |        /   Notes: The WS467 has a small
 |                                 |      /     1/4 watt resistor soldered
 |                                 |    /       between holes 1 and 2, as
 | |---------------|               |  /         well as an electrolytic
 | |     I C       |           |-| |/           capacitor soldered between
 | |---------------|  o 1      | |/|            holes 3 and 4. Remove these
 |                2 o          |-| |            components and solder a
 |                    o            |            jumper wire between holes
 |                   3   o         |            1 and 3 to restore local
 |                      4          |            dimming.
 |                                 |
 |                                 |
 |                                 |
 |                                 |
 |   (Other circuitry omitted      |
 |     for clarity.)               |
 |                                 |

          WS467 PC Board
          Component Side

        3. Once the switch has been disassembled and the PCB removed from
the case, examine the component side of the board closely while referring
to figure 1. Locate the small electrolytic capacitor and 1/4 watt resistor
located just below and to the right of the IC on the board. They share a
common connection. Note that there is probably a larger 1/2 watt resistor
in close proximity to the correct one - make sure you pick the right
resistor. Now flip the board over and locate the 4 pads to which these two
components are soldered. After warming up your soldering iron, use the
solder wick or desoldering bulb to remove the solder from those pads, and
remove the components from the board. NOTE: you could also simply cut the
components off the board, leaving the lead stubs soldered in place, but
desoldering the components will result in a much neater job.

        4. Again referring to the diagram in figure 1, install a small
jumper wire between holes 1 and 3. Solder the wire to the pads on the foil
side of the PCB.

        5. Reassemble the case, pop the circuit board back in, and pop the
back cover on. Turn the switch over and look closely into the hole where
the cutoff switch assembly fits. There you will see a pair of small metal
protrusions as well as a shorter metal contact area. Replace the small
metal tab into its position between the two taller metal protrusions,
positioned so that the other end of the metal tab can contact the shorter
metal contact area. Pop the cutoff switch assembly back into place, making
sure that neither the tiny spring-loaded rod nor the metal tab fall out
while you do so.

        6. Install the switch in the wall, and test normal operations
(local on/off control, remote on/off/dim control, and the function of the
cutoff switch).

        7. Finally, test the local dimming function: Press and hold the
button on the switch. The light will come on, and then slowly cycle through
a bright-to-dim-to-bright sequence. Release the button when the desired
level of lighting is achieved. A quick tap on the button will turn the
light on and off.

Q503. How do I modify the maxi-controller to accommodate more than 16

The maxi-controller controls 16 units on a single house code. For those of
applications with more than 16 units (and the thoughts of grouping units
together or gluing a dime to the house code select slot aren't that
appealing), a maxi controller can be made to control an alternate house
code with the addition of a momentary contact pushbutton.

The following procedure modifies the maxi-controller to use house code I
normally and control house code K with the push of a button.


        1. Open the maxi-controller. There is no need to remove the
circuit board.

        2. Install a miniature normally open momentary contact push button
switch (e.g. RS 275-1571A) in a hole *carefully* drilled in the back of the
top piece of the case so the switch will stick out the back when all is
done). Avoid the components and the mounting post. Position it roughly
behind the red LED on the Powerhouse brand of the maxi. Another way to
describe its location: If you have the standard label 1-16 in position, the
button goes behind approximately 12 (maybe a bit towards 11).

        3. Using a short jumper wire, solder one post of the switch to pin
7 of the IC (GI 8417) and the other lead to pin 10. Use as little heat on
the IC pins as possible to get a good solder joint without destroying it.

        4. Reassemble making sure nothing is shorting (jumper leads, etc.).

        5. Set house code rotary to position I and test units on house
code I. To operate house code K, push in pushbutton and hold it while
selecting the unit(s) and the operation (on,off,dim,bright,all lights on,
or all units off).

Note that the pins 7 to 10 mod will also allow you to control house codes
J/L, H/F, G/E, B/D, A/C, P/N, or O/M by changing the rotary switch.

Untried variations:  Using the chart below, you could connect via
pushbutton pins 7 and either 8, 9, 10, or 11 alternatively or more than one
if necessary to produce a desired combination. If you absolutely had to
produce a house code alternative where you need to turn a 1 into 0 instead,
you could use a normally closed pushbutton and cut a trace.

Maxi controller with GI 8417 IC (can jumper a "1" from pin 7)

 PIN     8   9   10  11
 ---    --  --   --  --

 J       0   0   0   0
 I       0   0   0   1
 L       0   0   1   0
 K       0   0   1   1
 H       0   1   0   0
 G       0   1   0   1
 F       0   1   1   0
 E       0   1   1   1
 B       1   0   0   0
 A       1   0   0   1
 D       1   0   1   0
 C       1   0   1   1
 P       1   1   0   0
 O       1   1   0   1
 N       1   1   1   0
 M       1   1   1   1

Q504. How do I modify the mini-controller to control more units?

This answer should be read in conjunction with the instructions for
modifying the maxi-controller in Q503.

Unfortunately, the truth table for the mini-controller appears to be all
different for that for the maxi-controller, and there isn't a real good
place to mount the pushbutton. Besides, if you really need to control a
bunch of units, you wouldn't have the mini-controller in the first place.

However, the following seems to apply:

Mini controller with 8925 IC (can jumper a "1" from pin 3)

 PIN     5   6    7   8
 ---    --  --   --  --

 M       0   0   0   0
 O       0   0   0   1
 E       0   0   1   0
 G       0   0   1   1
 C       0   1   0   0
 A       0   1   0   1
 K       0   1   1   0
 I       0   1   1   1
 N       1   0   0   0
 P       1   0   0   1
 F       1   0   1   0
 H       1   0   1   1
 D       1   1   0   0
 B       1   1   0   1
 L       1   1   1   0
 J       1   1   1   1

Q505. How do I modify the mini-controller to control all units for a
single housecode (i.e. all "bands")?

The X10 mini controller is capable of addressing four of the sixteen X10
unit codes. A slide switch on the controller allows the user to select the
"band" of units 1-4 or 5-8. A simple modification allows the selection of
two additional bands, 9-12 and 13-16. This covers the entire spectrum of
X10 units accessible from a single house-code.

This modification applies to the "Radio Shack" branded mini controller,
number 61-2677B. By visual inspection of the circuit board and internal
components, it appears that this modification also applies to "Stanley"
branded mini controller number 360-3090. It appears that both of these
units were manufactured for X10 for sale under the distributors' own brand
name, and are essentially identical inside.

There was an earlier model of the mini controller that was available from
Radio Shack, and possibly other sources. Legend has it that the old unit
was even easier to modify for access to all four bands. In fact, one
legend says that the unit was equipped with a four-band switch, two
positions of which were simply blocked off by the plastic bezel sticker
applied over the plastic cabinet. I don't know what the truth is, not
having one of the old mini controllers to study. What I do know is that
this modification was not developed for the old controller.

The old mini controller had four switches for the unit codes, plus
individual switches for ON, OFF, DIM, BRIGHT, ALL LIGHTS ON, and ALL UNITS
OFF. To turn on unit three, one would depress two switches:  3 and ON.

The new mini controller does not have ON and OFF switches apart from the
unit codes. Instead it has an ON and OFF switch for each of the four unit
codes. (In the case of the Radio Shack unit, there are four rocker
switches, up for ON and down for OFF. The Stanley unit has individual
switches for 1 ON, 1 OFF, 2 ON, 2 OFF, etc.)  Pressing one of these
switches sends both the unit code and the ON or OFF command. The user can
then follow up by using the DIM or BRIGHT switches, or the ALL LIGHTS ON or
ALL UNITS OFF switches.


        1. Unplug the unit and open the case by removing the four
phillips-head screws. Put both halves of the case in a safe place. When
handling the printed circuit board, observe the usual precautions for
static-sensitive devices.

        2. Locate the place where the existing "band" switch is located.
This is nothing more than a plastic handle on a metal slider that runs in a
trough molded into the top part of the case. The slider makes contact with
three large pads on the printed circuit board.

        3.The hardest part of the modification is finding a new switch to
use for the four-position band selector!  It is possible to use a two-pole
four-throw rotary switch. I'll let you figure out how to do the encoding
if you decide on that. I found a suitable switch in my junk-box and
mounted it in a position that replaces the old band switch. This entailed
some amount of cutting and gluing on the plastic case. I will assume that
you are doing the same. Find a small slide switch that has four positions.
It should have two rows of five contacts. As the switch is moved, it
should short two adjacent contacts at a time. Looking into the pins in the
back of the switch, one should see the following connection pattern for
each switch position:

     position 1         position 2         position 3         position 4
   +-------------+    +-------------+    +-------------+    +-------------+
   |1--2  3  4  5|    |1  2--3  4  5|    |1  2  3--4  5|    |1  2  3  4--5|
   |             |    |             |    |             |    |             |
   |A--B  C  D  E|    |A  B--C  D  E|    |A  B  C--D  E|    |A  B  C  D--E|
   +-------------+    +-------------+    +-------------+    +-------------+

Physically, the switch should fit in pleasingly with the rest of the panel.
This usually means that it should be rather small. This is a good time to
decide exactly where to put it. The most logical place is directly in place
of the existing band switch. This may require hacking away part of the
printed circuit board.

        5. Orient the printed circuit board in front of you, such that the
foil side is down, and the power cord attaches to the board on your left.
The big chip should be slightly right of center, and most of the components
will be near your belly. Make sure that the chip has 24 pins, and is
marked 78567. To your right of the chip is a small metal-can transformer.
Further right and up, should be an electrolytic capacitor, around 1000 mFd
at 25 V. The capacitor's negative lead is well marked. Locate the
positive lead.

        6. If the new switch does not physically replace the old one,
disable the old switch by removing the slider from it.

        7. Looking into the back of the switch, wire pin A to 4 to IC pin
11. Wire switch pin B to 3 to D to the + lead of the capacitor. Wire
switch pin C to IC pin 12. The result should look something like this:

      |            |
      |  +---------|---+
      |  |1  2 _3_ 4  5|
      |  |    /   \    |
      |---A  B  C  D  E|
      |  +------|--|---+
      |         |  |
      |         |  `-----> to capacitor +
      |         `--------> to IC, pin 12
      `------------------> to IC, pin 11

The intent of this circuit is to impress one of four binary codes on the
IC's pins 11 and 12. This tells the controller chip which band of X10
units to address. The logic levels to be presented to the chip are
provided by dead air and the + lead of the electrolytic capacitor. The
truth table is:

   unit     switch     switch    |  pin 11   pin 12
   band     position   shorting  |  sees     sees
   -----    --------   -------- -+- ------   -----
    1-4        1       1&2, A&B  |  cap      air
    5-8        2       2&3, B&C  |  air      cap
    9-12       3       3&4, C&D  |  cap      cap
   13-15       4       4&5, D&E  |  air      air

        7a. Rotary switch option. This version is untested, but should
work. It is for rotary switch lovers out there. Get a 2-pole 4-throw
rotary switch and wire it as follows:

        .------------------------------> to capacitor +
        |     |              |  |
        1_ 2  3  4        1_ 2  3  4
        |\                |\
          \- - - - - - - - -\
           \                 \
            O                 O
            |                 |
            |                 `--------> to IC, pin 12
            `--------------------------> to IC, pin 11

You probably want to avoid binary or BCD-encoded thumbwheel switches because
the base station coding scheme is offset slightly from normal binary coding
(and the switch output). You would have to relabel the switch positions, not
to mention blocking off the unused positions.

        8. Put the box back together. Screw it shut again before applying
power. Try it out.


Q506. How do I modify the mini-controller to control only units 9-12 or

Read in conjunction with Q505.


        1. Open mini-controller and pull back the circuit board. Be
careful not to let all the switch tops fall out.

        2. Locate the three pads underneath the slide switch. Notice that
the unmodified mini selects 1-4 or 5-8 depending on whether the center
position makes connection with one side or the other.

        3. To modify the mini to control only units 9-12, solder a jumper
such that all three pads connect together.

        4. To modify the mini to control units 13-16, simply remove the
slide switch.

Untried variation #1: If you solder the jumper as to not interfere with the
slide switch, then you could jumper just one side and then use the slide to
select 1-4 or 9-12 or .. jumpering the other side, 5-8 or 9-12.

Untried variation #2: If you mangle the slide switch so that it only has
the contacts on one side or the other, you could use the slide switch to
select 1-4 or 13-16, or .. removing the other side 5-8 or 13-16. A possible
problem here is that the half-mangled slide switch may not "sit right".

Q507. How do I modify the mini-controller for momentary operation?

The following answer comes from


When a Mini-Controller is modified as below, your key presses are undone as
soon as you release the key. Thus pressing 'on' and then releasing, sends
an 'ON' and then a 'OFF' command. This is also true for 'All Unit'
commands. This mod only works on model 'MC460' Mini-Controllers, and not
the 'MC260' (If anyone knows how to identify the two, please post).


Inside the mini controller, connect pin 3 and 14 of the black IC marked
78567. You may want to make the connection with a little switch to return
the controller to normal mode.

Q508. How do I repair a "blown" X10 lamp module?

X10 lamp modules have a bad habit of dying premature deaths. Most of the
time, the problem can be traced back to a bad triac. Why the triac is the
weak link has been debated hotly. It is possible to "resurrect" the module
by simply replacing the triac. Caution must be stressed here; there are a
lot of triacs available, but whichever one you use must have an isolated
tab. The most universally available replacement is from Radio Shack, part
number 276-1000 [Does this part actually have an isolated tab?], or Digi-
Key part number L4008L6-ND. In addition to having an isolated tab, it also
has a higher rating than the original one, so will be less likely to fail.

If you don't know a triac from a mouse trap, you'd better not try to
replace it.

Q509. How do I defeat local control of lights and appliances?

A standard appliance or lamp module will turn itself on if the power switch
on the device it is connected to is switched on. This provides local
control. This is not always desirable, however. Local control depends on
the current draw through the module; if it exceeds a certain value, the
device turns on. Some devices (compact fluorescent lamps, for example)
seem to have low impedance and keep switching themselves on even when
explicitly turned off. This local control can be disabled for appliance


        Inside each module, there is an integrated circuit labeled "PICO-
570" or "PICO-536C"  Cut the lead that goes from pin 7 of this integrated
circuit to the hot AC connection.

Q510. How do I add a relay output to the power horn?

The following answer comes from


I have always wanted to add a relay output to the power horn. With this
feature, I can switch on a more powerful outside bell, an autodialer, or
any other load upon detection of a violation. When I opened the case, I was
surprised to learn that unit was already designed to do just that, except
the necessary components have been left out. There even are two holes in
the back of the unit for screw terminals that are covered by a small
sticker. After tracing the circuit, I selected some replacements listed


The procedure requires the installation of eight components that should be
commonly available. Open the case by removing the four screws in the back.
On the PC board you will see near the bottom (side away from the AC plug)
the silk screening for the relay output portion. Install the following
components (all resistors 1/4 watt with exceptions):

  R30 - 1Kohm (1/2Watt)
  R32 - 12Kohm
  R33 - 12Kohm
  R34 - 200Kohm
  R35 - 200Kohm
  D16 - Any Silicon Diode (not Zener)
  RL1 - Your relay (see note below)
  TR8 - 2N2222 Switching Transistor

For the screw terminals, you can use a set taken from an unused (X-10)
alarm sender, or you can decide on your own interface. The relay could be
tricky. I was lucky and was able to find a relay that fit after some
modifications. It does appear to me however that Radio Shack sells micro
relays that would fit.


The relay will close as soon as the horn starts blaring (and vise versa).
Your current rating will certainly depend on the relay you choose. If you
are so inclined, you could even disconnect the piezo horns, and have a unit
that silently turns on a load upon an alarm violation.

Changing the reaction time of the Horn:

After some poking around I found out specifically how the Horn is
triggered. A capacitor is charged a small amount every time an ALL UNITS
OFF command is received after an ALL UNITS ON command. When this voltage
reaches 7.0 Volts, the Horn starts a-blarin'. This usually takes 20
seconds after the alarm system is triggered, an amount that I think is just
too long. The capacitor that determines the reaction time is C13, located
near pin 18 of the 78566 chip. The 'stock' value of this capacitor is
22uF, and it takes five transitions of the command to trigger the horn. By
using a 10uF capacitor this amount is reduced to only two needed
transitions. Summary:

        Standard Horn (22uF) trigger time is 20 seconds.
        Modified Horn (10uF)                 8  seconds.

The quick reaction time will hopefully cause the intruder to stop his break
in attempt sooner.

Effects of Combining the two Mods:

If you want the load that is switched by the relay be flashed on and off,
you can combine the two modifications. The on to off duty cycle can be
changed by changing C13. Actually what I have done is to socket C13, so
that I can open the case and easily change the reaction time of the horn.


I ( am curious to know if anyone finds this mod
useful. Please let me know any questions or comments. Have fun, and I
will trust that you will not hold me responsible for your failures (only
for your successes 8-).


One of the great shortcomings of the X-10 wireless security system is the
lack of an interface to external devices, like a strobe and/or siren, to
alert neighbors of a burglary or other emergency situation. The following
modification adds that capability.

When an alarm is activated, the base (receiving) unit wails its siren and
sends out alternately, at about one second intervals, the signals ALL
LIGHTS ON, ALL UNITS OFF. This has the effect of flashing all lights on
the same house code. You can buy a remote, plug-in power siren which has
been designed to trigger when it receives 4-5 on-off cycles, alternating
its two-tone horn in synch with the ON-OFF signals. However, it is not
suitable for outdoor installation.

As noted by others, the power siren circuit board contains space for an
optional external relay interface circuit, although units with this option
seem never to have been produced. It would provide a low-voltage contact
closure (30VAC, 2A max.).

In this note I will describe how to make the modification, based on
schematics from X-10 engineering and my own testing. This improves upon
earlier recommendations in the X-10 FAQ.


Install the following components in their marked location on the circuit

    R30      470 ohm 2 watts     do not allow to touch other components
    R31      2.7 K   1/2 watt    just fits: do not substitute or leave out
    R32      2.7 K   1/4 watt
    R33      100 K   1/4 watt
    R34      100 K   1/4 watt
    R35      150 K   1/4 watt
    R36      1 K     1/4 watt
    C18      10 uf   16 volts    + on board is marked with a diamond
    D16      1N4001  1 AMP diode
    TR8      TEC9014 (almost any 100ma NPN switching transistor will work)
    RL1      5 volt, 72 ma DIP relay, Radio Shack #275-243

Remove R8 (or just clip the leads). There may be a resistor in parallel
with R8, remove it also. This was used to keep the unregulated and
unloaded + supply from floating up too high, and is now taken care of by

Activated (and unmodified), the unit consumes about 70ma, powered on the -
side by a 100ma regulator. The relay modification consumes an additional
70 ma, over-taxing the power supply and regulator. Even though it will
still work for a brief time when activated, you risk having the regulator
shut-down or the transformer overheat. To get reliable operation within
safe-area limits, change the wiring to the piezo elements. The unit comes
from the factory in which all four elements are wired in parallel. Change
the wiring so that they are in a series-parallel configuration, reducing
their current drain from 50ma to 12.5ma, and reducing their total sound
level from 105db to 99db.

             --| |--    --| |--
          __/       \__/       \__      (piezo element wiring change)
            \       /  \       /
             --| |--    --| |--

You should maintain consistent polarity when rewiring the elements, and if
you are clever, you can do it by removing one brown wire at the top, switch
the polarity of the other brown wire at the top, and use the wire you
removed to relocate and extend the blue wire to the opposite side (cover
the exposed connection). Since you are going to hook up an external siren
presumably, the loss of indoor volume should not pose a problem (I think
it's too loud anyway).

Finally, you need to install screw terminals in the slots provided. I used
terminals taken from an X-10 door/window sensor in which I permanently
soldered the wires connecting to the magnet. Before installing them, you
must break off the side tabs which are on top and next to the screw,
otherwise the rear cover of the case won't fit. They don't quite stick up
as high as I'd like, so if anyone has a better source of screw terminals
I'd like to know. Now, remove the adhesive cover plate on the rear cover,
and write in red marker next to the terminals "30 volts, 2 amp max."

Please send corrections, suggestions, experience to .

Q511. How do I change the crystal in my CP290?

From a post by

  I wondered about the accuracy of the internal clock in the CP-290.
  Necessity being the mother of invention, I have figured out how to increase
  the accuracy at least tenfold. Instead of drifting 30 seconds per
  week, my CP-290 now drifts less than 30 seconds a year.

  The CP-290 is clocked by a two-transistor crystal oscillator running at
  32.768 kHz. The power consumption of this oscillator is very low, which
  allows the CP-290 to run on battery backup for long periods. This
  oscillator is used to run the clock whether or not it is connected to AC
  power, i.e., the power line frequency is not used.

  To open the CP-290, unplug it and remove the battery. Next, remove the
  four screws holding the case together, one in the battery compartment and
  three under the rubber feet in the remaining corners. Remove the battery
  compartment and the screw near the power transformer that holds the main
  circuit board in place. When removing the main circuit board, watch out
  for the ribbon cable. It's pretty stiff, and the wires might break if you
  flex it too much.

  To improve the accuracy of the clock, I removed the original 100 ppm watch
  crystal and replaced it with a 20 ppm part (Digi-Key sells several).
  Next,I removed 33 pF capacitor C17 and replaced it with a 15 pF fixed
  capacitor in parallel with a 5-15 pF variable capacitor. I used NPO
  ceramic capacitors for maximum temperature stability.

  The oscillator circuit is located along the right side of the circuit
  board, about halfway between the ribbon cable and the battery compartment.
  The crystal is a small cylinder about 1 cm long and a few mm in diameter,
  and is covered by a blob of silicone to keep it in place. After installing
  the new parts, I removed the solder flux with alcohol so the stray
  capacitance of the flux wouldn't affect operation.

  To trim the oscillator, I used a frequency counter with 0.1 ppm accuracy.
  The clock signal can be probed at the end of R35 nearest to the battery
  compartment, or at wire jumper L21 near tuned transformer TC3, or on pin 39
  of the 80C48 microcontroller IC1.

  People who don't have access to a good frequency counter/standard will have
  to trim the oscillator the old fashioned way: by trial and error. If this
  is the case, you might want to program the CP-290 to turn off a non-
  existent module once an hour. The LED on the front panel will blink each
  time the CP-290 transmits, which will allow you to determine whether the
  clock is drifting.

  When adjusting the frequency, keep the CP-290 at the same temperature at
  which it will normally be operated, and allow the circuitry to warm up for
  at least 10 minutes first. It doesn't matter whether you run it on battery
  power or AC because the oscillator's supply voltage is regulated. I
  recommend using battery power for safety.

  You may have to use different capacitor values depending on how far and in
  what direction the frequency is off. Lower values of C17 make the
  oscillator run faster, and higher values make it run slower. If you make
  C17 too small, the oscillator won't run at all. You can tell whether the
  oscillator is running because the front panel LED will blink every few
  seconds when the CP-290 is on battery power. If it doesn't blink, the
  oscillator isn't running. Also, if you try to change the frequency too
  much, the oscillator will become unstable and drift with temperature. This
  happened to me with the original crystal, which is why I replaced it with a
  better one.

Q512. How do I repair a broken wall switch module?

From a post by Edward Cheung:

In most cases, the failure was in a hiwattage resistor near the 'bottom'
of the module. Look at how a wall switch is normally mounted inside a
wall box.  Call the part closest to the floor the 'bottom'.  When you
disassemble the wall switch, look for a 1/2 watt ~68Ohm resistor near
the bottom of the module.  If it has a brown crack on it, you know that
you have located the overheated/dead part.  Replace it with a 1 watt

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