StewMac MXR PHASE 90 User manual

MXR PHASE 90
SCRIPT MOD
INSTRUCTIONS

THIS MOD GIVES
YOU TWO SOUNDS
FROM YOUR STOCK
PHASE 90.With the ick of a switch
you can have your stock“block” sound and the
coveted vintage “script” sound that you’ve heard on
thousands of recordings. It’s like getting two pedals
in one.
If you run into issues with this modication,
a StewMac tech advisor is a click or call away:
stewmac.com/contactus or 1.800.848.2273
MXR is a registered trademark of Dunlop Manufacturing Inc.

Guitar Tech Screwdriver
and Wrench Set
#3693
Hammer & metal
punch or nail
Kester Pocket-Pak Solder
#0505
Solder Sucker
#0503
Solder Wick
#0504
PARTS LIST
[1] Black and white
pushback wire
[2] 1/8" heat shrink - 2" length
[1] Mini toggle switch
[1] MXR Phase 90 Script
Mod instructions
Fine-gauge
Wire Stripper
#1606
Wire Cutter
#1607
1/4" Drill Bit
#4850
Solomon
SR-965
Soldering Station
#0501
TOOLS YOU’LL NEED

CONNECTING THE NEW SWITCH
For your new switch to be connected properly, an understanding of tinning and soldering is necessary.
TINNING
Tinning is an important part of the soldering process as it helps to make stronger solder joints. Tinning a
wire is done by heating the wire with a soldering iron and then melting a layer of solder on it. If the wire
you plan to tin is made up of many strands of wire, follow all of the steps below.
1. Strip roughly 1/4"of
the wire sheathing from
the end of the wire you
intend to solder.
2. Twist the wire
strands of the exposed
wire rmly. Don’t twist
solid core wires.
3. Dab a tiny amount
of solder onto the end
of your soldering iron.
4. Touch the soldering
iron with its dab of
solder to the exposed
wire closest to the
sheathing. This will help
to hold the iron in place
as it heats the exposed
wire. Wire will heat
within a few seconds.
5. With the iron still touching the wire, take a
length of solder and touch it on the exposed end
of the wire and slide it along the wire slightly
towards the sheathing and iron. The solder will
nd its way into the braids of the exposed wire.

MORE HELPFUL
SOLDERING TIPS
AND TRICKS
•Keep your
soldering tip clean
by wiping it often
on a damp sponge.
• Also keep it tinned by
occasionally melting
a little solder onto it.
•Don’t blow on the
hot solder or touch
anything until the joint
has cooled completely.
A good solder joint
is shiny – a sign that
it was left to cool
undisturbed.
• Plan so each joint
is only soldered once.
Resoldered joints
are messy and more
likely to fail.
SOLDERING
1. Insert tinned wire through lug hole
before soldering and bend to secure.
2. Melt a small amount of solder onto
the tip of the iron (“tinning” the iron).
3. Hold the tip against the connection
until the connection reaches soldering
temperature. This should take just a
few seconds.
4. Feed solder to the connection, not
to the iron. Stop feeding solder once
the lug hole is lled. Keep the iron on
the connection for a second longer;
this pause gives time for all of the ux
to cook out of the joint. After the joint
has cooled, trim away the excess wires.

DESOLDERING
Much like soldering, you run the risk of damaging the circuit board while desoldering. If too much heat is
applied to a circuit board the solder pad can pull away from the board, breaking its electrical connection. A
solder sucker and solder wick are your best friends when desoldering. Here are a few tips on how to use them:
1. USE A SOLDER SUCKER
Depress the plunger on the solder
sucker to prepare it. Tin your
soldering iron, apply it to the
solder joint, and hold the solder
sucker a fraction of an inch away.
Within a few seconds, the joint
will liquefy. As soon as it does,
push the button on the side of
the solder sucker and remove
the soldering iron from the joint.
Inspect the solder joint and
repeat the process until all of the
solder is removed.
2. USING SOLDER WICK
Solder wick is a at, braided
wire that can be used to remove
solder from a joint. Simply place
the wick on the solder joint and
press your soldering iron against
the wick, heating the joint
through the wick. The solder will
liquefy and absorb into the wick.
Keep inching the wick down as
it absorbs solder so it does not
become saturated.
3. LIFT THE LEAD
Once the solder is removed from
the joint, use a pair of pliers to lift
the lead from the circuit board
contact. If the lead doesn’t want
to come up, heat the solder joint
up to liquefy the residual solder
which will free the lead. Once
the lead is lifted, use the solder
sucker or solder wick to remove
any leftover solder.

DISASSEMBLE THE PEDAL
Remove the four screws that
secure the back of the pedal
housing. Pull the knob o of
the front of the pedal, unscrew
the mounting nuts for the
potentiometer and the switch,
and unscrew the mounting
nuts for the instrument and
power jacks on the side panels.
Gently push the switch and the
pot shaft from the front of the
enclosure and the board should
come right out.
MXR
phase 90
INPUT
OUTPUT
SPEED
11

R28
LOCATE R28 ON THE PCB
R28 is the resistor just above the output jack.
Desolder and lift the leg of R28 that is closest to
the edge of the board (pictured). If you are having
trouble suciently heating the solder, ip the board
over and desolder the back of the pad. After the
solder has been removed from the pad, carefully
lift the resistor leg from the pad. To do this you
might need to heat the leg and the pad with your
soldering iron. Be careful not to break the other leg
of the resistor as you are lifting the left one.
In the next steps you will prepare the switch to
attach to the R28 resistor. The switch will take the
resistor in or out of the circuit, letting you change
between the stock “block” sound and the vintage
“script” sound.
22

INSTALL A WHITE WIRE ON THE SWITCH
Cut one 2" section of white wire, strip roughly 1/4"
of insulation from the end of it, and tin the freshly
exposed wire. Wrap the wire through the eyelet of
one of the outside solder lugs on the switch and
solder it. Even though it's called“pushback wire”
you must strip the insulation to make a solid solder
connection.
INSTALL A BLACK WIRE ON THE SWITCH
Cut one 2" black wire, strip roughly 1/4" of
insulation from the end of the wire, and tin the
freshly exposed wire. Wrap the wire through the
eyelet of the middle solder lug on the switch
and solder it.
3344

HEAT SHRINK SOLDER JOINTS
Add a 1" length of heat shrink to each solder joint
and use a heat source to shrink the insulation over
the solder joints and wires.
55TIPS ON HEAT SHRINKING
1. Heat shrink is used
to insulate an
electrical connection,
like a solder joint, to
prevent the connection
from shorting.
2. Slide the heat shrink
all the way up to the
switch, completely
covering the solder joint
and solder lug.
3. Wave the ame from
a lighter or the tip of a
soldering iron near the
positioned heat shrink
until the wrap constricts
to a rm hold. Allow
heat shrink to cool.

INSTALL THE BLACK WIRE
Slide another 1" length of heat-shrink over the
black wire that you just soldered to the new switch.
Solder the free end of the same black wire to the
lifted leg of R28. Use a heat source to shrink the
insulation over the joint you just soldered.
INSTALL THE WHITE WIRE
Feed the free end of the white wire through the
hole vacated by the lifted leg of R28. Solder this wire
to the solder pad on the back of the circuit board.
6677

1/2”
1-3/8”
DRILL A HOLE FOR THE
NEW SWITCH
Measure approximately 1-3/8"
down from the top of the pedal
enclosure and 1/2" over from
the side of the enclosure. Mark
this location with a nail or a
center punch to help keep your
drill bit in place while you start
drilling the hole.
Use a 1/4" drill bit to drill a hole
in the pedal enclosure where
you just left a mark.
88

FINAL ASSEMBLY
AND TESTING
To install the switch, guide it
into its hole rst, positioning the
body of the switch so the switch
will ip side to side and not up
and down. Once the switch is
secured, then reinstall the rest of
the components back into the
pedal housing.
Re-attach the back panel with
the four mounting screws. Plug
in your guitar and an amp, and
take your MXR Phase 90 for
a test drive. When the switch
is engaged, the pedal should
be noticeably warmer and
less harsh. If you experience
intermittent signal or other
irregularities, pull the back panel
o the pedal again and inspect
your solder joints.
MXR
phase 90
INPUT
OUTPUT
SPEED
99

21 N. Shafer St., Athens, OH 45701
800-848-2273 stewmac.com
©2019 StewMac. All rights reserved. • #2217 Updated December 2019
TECHNICAL SUPPORT:
If you have any questions before, during, or after
attempting these modications, please don't hesitate
to reach out to our Tech Support Team. They are
available by email at [email protected]om, and by
phone M-F 9:00AM-5:00PM ET at 1-800-848-2273.
DISCLAIMER: Performing the modications
outlined in these instructions will void any warranty
on your pedal. StewMac is not responsible for any
damage caused by attempting these modications.