Ibanez Compressor Pedal CP10 Repair

Mysteriously, this pedal just went mute while playing.  Can the Unbrokenstring Crew get it going again?

I find this to be a unique design.  But I cannot help but think that the assumption was made that everyone uses their right foot to run the pedal.  Using your left foot is a little awkward.

 

Let’s make a quick tour of the unit.  The pointers on these molded knobs are actually easy to see when the unit is on the floor.  The LED indicates that the unit is in circuit and active.

 

Pushing this little tab out allows the pedal pad to open.

 

The 9v battery goes here.  This switch is actually soldered to a small circuit board underneath.

 

Removing the bottom cover exposes the circuit board.  The black shiny sheet in the middle is an insulator.

 

The circuit board tips out like this.  But, there’s more!

 

The controls are located on a smaller circuit board underneath.  Out it comes!

 

These bushings align the shafts of the controls in the holes.  They just push in like grommets.

 

Now we can get to everything.  The switch itself is left installed in the housing.

 

Troubleshooting begins, using my massive Marshall Stack as an output indicator.

 

The signal is traced to here.  And then the signal disappears.  Can you see it?  I can’t either.

 

This capacitor is open-circuit.  No signal shall pass this way again.

 

Here is a replacement.

 

The replacement goes here.

 

The new cap is soldered in and the flux is cleaned away from the board.  Because I’m OCD like that.

 

Everything is working again.  We’ll put this unit back together and do a final test!

 

This looks no different than the first picture.  Except, this one works.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Wireless Shure SM58 Battery Leaked

This microphone was part of the estate of an amateur journalist. As she moved into treatment and into hospice, there were other concerns besides removing the batteries from unused equipment. Could the Unbrokenstring Crew revive this unit and make it usable again?

This microphone is a basic SM58 capsule coupled to a battery-operated VHF FM transmitter.

These are often seen in many performance venues as well as in worship, news-gathering, and business settings.

 

The 9v battery has leaked.  We will need to disassemble the unit to clean up the mess.

 

These VHF units are on frequency allocations that are shared with other services and may be subject to interference.  However, these units work well if you are fortunate enough to be in a part of the country where interference is low.

 

The microphone capsule is built into the head of the microphone, which unscrews from the electronics.  Connections between the capsule and the electronics are reliable regardless of how many turns are necessary to tighten the threaded bodies together.

 

The gold fingers touch those rings seen in the previous picture.

 

This inside snap ring keeps the electronics inside the housing.

 

Before we remove the electronics,we need to get the switch actuators out of the case.  The cover removes easily enough.

 

The switch actuators come straight out.

 

This is looking good!

 

This is the complete analog FM transmitter.

 

Working with the battery contacts is much easier now that the case is out of the way.

 

Reassembly is the reverse of disassembly.  Wow, that’s profound…

 

These big tweezers are all I need to get the inside snap ring back in place.

 

Reassembled, the new battery is installed and we have a green light!

 

The receiver indicates that an FM carrier is present.

 

We have an intermittent problem with audio out of the microphone.  We need to look at the capsule.

 

I guess we’ve screwed the pooch by now.

 

The wires are cracked where they emerge from the solder joints.  These will be reworked.

 

This brass adapter goes between the capsule and the rest of the housing.

 

We are back together again!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Maxtone CB Wah Wah Pedal Repair

George had this wah pedal in his collection but realized one day that it didn’t work.  Could the Unbrokenstring Crew help?

These pedals are common but there is very little literature available on them.  That won’t stop us!

 

On the bottom of the unit, we find this text.

 

And, we find this text.  Not made in PRC (Peoples Republic of China!)

 

The power jack is the older mono 3.5mm jack often seen on period pieces such as this.

 

Peering between the pedal and the base, we see the rack and pinion that runs the potentiometer, and the bypass switch.

 

When we open the unit, we see that the potentiometer has come loose from its mounting fork.  The battery has not leaked.  In fact, it’s still reading nine volts!

 

You can see the fork where the potentiometer mounts.  All of the hardware is present and accounted-for.

 

We have re-mounted the control where it belongs.  This requires some adjustment, as we will see later.

 

From the outside, we can more clearly see the rack and pinion that drives the potentiometer.  Also, the bypass switch is really high.  This needs to be adjusted first so that it switches only when the pedal is all the way down.

 

Here we see the bypass switch is mounted much lower.  When the pedal is pressed downward, we hear a clean ‘click.’  This is an indication that it is adjusted correctly.

 

On the inside of the unit, the jam nut is tightened so that the switch stays in this position.

 

A little bit of petroleum jelly serves as a lubricant for the rack and pinion.  The screw to the right adjusts the mesh ‘pre-load,’ keeping the teeth aligned, yet minimizing the sideways load on the shaft bearing inside the potentiometer.  The gears are ‘slipped’ until the desired portion of the pot shaft rotation is in the correct place (relative to the pedal) to give us proper ‘wah’ action.

 

The actual ‘wah’ circuit is little more than a treble boost/cut circuit.   Now that everything is together, the unit is tested with a guitar and amplifier.  Now that we have confirmed that the portion of the pot rotation is OK for this unit, all the screws are tightened.

 

George said that he installed a new battery, so this one stays.

 

We are all back together and ready to return to the pedal board.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Ibanez / Stratus TS-9 Clone Pedal Repair

What do we have here? This pedal is completely custom inside and out.  Who made it?  And why does it not work?  Can the Unbrokenstring Crew decipher this jewel and get it working again?
Matt received this as a gift after a live show, from an appreciative fan.  It has an honored place on his pedal board.

 

Google is of absolutely NO help deciphering any of this text.

 

Very nice circuit board!  This is a Tube Screamer circuit, with several types of LEDs and diodes selectable in the clipping circuit.  Nearly every aspect of the circuit topology is ‘bend-able’ in this pedal.  Very cool!

 

This unit uses a very nice, high-quality Burr Brown operational amplifier chip and precision components throughout.

 

Our principle problem is immediately apparent.  See the broken wire on the output jack?

 

We have another broken wire on the switch.  Solid (unstranded) wire is easy to work with, but is prone to cracking and breaking more quickly than stranded wire.  But solid wire is widely used in the pedal building world.

 

Stratus is a supplier of ‘build your own clone’ pedal kits.  Their catalog confirms that this is a Tube Screamer clone.  Oh, and we found more broken wires.

 

The common ground circuit at the output jack relies on the conductivity of the enclosure.  When the enclosure is painted, as this one is, one can have an intermittent electrical connection.  Here, I’ve removed the jack to scrape some paint and add a toothed lock washer for better connection to the pedal enclosure.

 

This tool is handy to keep jacks from turning while the nut is tightened.  These are designed for hollow-body guitars, but work almost anywhere a quarter-inch jack is found…  for instance, here.

 

I wonder whose cat this is?

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Sovtek Small Stone Pedal Refurb and Update

The modulation rate control on this wonderful Sovtek Small Stone phaser effect pedal had broken. While the unit is in the shop, could the Unbrokenstring Crew also add a 21st century DC pedal power jack to the unit?

Like a message in a bottle, this pedal has the look and feel of a relic from another planet. Even the switch looks like alien technology.

Removing the top cover reveals a heavy steel plate that holds the major components.  Look at the LED holder!

The control for the phase modulation had disintegrated.  Not much was left holding the shaft in place.

The back side of the modulation control was not out of the ordinary beyond the Cyrillic alphabet. Perhaps it could be rebuilt using parts from another similarly-sized potentiometer.

We have removed the old potentiometer from the circuit.

The tabs on the back cover of the potentiometer can be peeled back in order to disassemble the unit.

Interestingly, the internals of this control are completely different than what we might expect from a domestic control.  This potentiometer is a ‘reverse audio taper’ component.  The Russians achieved this by mounting the resistive element on the opposite side of the main wafer of the control, effectively reversing the direction of the taper.

So, it appears that we need to find a control that is close to the physical size of the old part, so we can reuse the knob.

We are working in millimeters here, in case you are wondering.

An aluminum bushing allows this smaller shaft to fit in the Russian knob.  Perhaps we have another degree of freedom in our search for a proper replacement.

This bushing can be removed…  a good thing that will allow us to do some gun-smithing if we need to do so.

The knob is not quite big enough to allow a quarter-inch shaft to be substituted.

So, we located a reverse audio taper control custom-designed for Neve recording consoles.  Yeah, I got connections.

This part has an appropriately-sized shaft that will permit us to use the original knob.  Good news!

The new control is wired into the circuit in the same manner as the old one.  Teflon spaghetti tubing handles the high-temperature insulation duties here.

These little spacers were rattling around in the enclosure after the circuit board was removed.  Where do these go?

Turns out, they are spacers that go on top of the cast bosses in the bottom of the original box.

The new power jack is mounted and wired into place, along with new steel Switchcraft in and out jacks.

The whole arrangement is now fitted back into the case.

An internal nine volt battery is used for powering this unit for checkout.

We have a winner!  Time to tighten down the screws and button this unit back up.

Here is the top cover with the new control installed.

The case cover is now back on.

The owner wanted to leave no question regarding whose pedal this was.  Mine!!!  Mine!!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

 

Digitech GSP1101 Effects Processor Repair

A frantic spouse called to explain that she was vacuuming and hit this ‘thing’ and broke this little piece off it.  Could I fix it before her husband found out?  The Unbrokenstring Crew to the rescue again!

01GSP brokenThe gain knob on this unit is a rotary encoder.  This component is available from several vendors.

02GSP what to doShe kept the knob, which is GREAT news, because although the rotary encoder is available, the knob is not.

03GSP salvage knobThe remains of the shaft of the rotary encoder was removed from the knob.  So far, so good.

04GSP opensesameLet’s get to work replacing the broken rotary encoder.

05GSP knobs offAs is the usual case, all the knobs come off first.

06GSP board looseThe circuit board lifts away easily.

07GSP spacer1These cool little plastic spacers set the geometry of the rest of the buttons and controls.

08GSP spacer2We will put this piece away somewhere safe while work elsewhere continues.

09GSP remove oldTo minimize the stress on the circuit board while removing the old component, the body of the broken rotary encoder is cut away from the component leads at an angle perpendicular to the circuit board.

10GSP part goneWith the component cut away from the circuit board, de-soldering the legs becomes trivial.

11GSP clear backThe component legs are gone.  This is a high-quality circuit board, double-sided copper and plated-thru holes.

12GSP clear frontBoth sides of the circuit board are cleaned up.

13GSP new partHere is the new part, ready to be soldered onto the circuit board.

14GSP reassemble1We are ready for reassembly.  That plastic spacer is re-installed as it was before.

15GSP reassemble2The cable carries all the signals back and forth to the front panel.  I like this bit of orgami.

16GSP reassemble3The circuit board is held in place by the bodies of the controls, which are in turn bolted to the front panel.

17GSP knobs onEverything is back together, ready for testing.

18GSP power onThis looks good!  While we were at it, we will do a factory reset.

19GSP final testNow, everything is as it once was.  And the husband was scolded for leaving his toys on the floor, where she could hit them with the vacuum.  Maybe I could sell him a rack case?

Thanks for reading all the way through!

CONTACT – David Latchaw EE
281-636-8626

Vintage Boss Chorus Ensemble Pedal Refurb

Wonderfully-preserved from the era when one could still see Stevie Ray Vaughn perform live, we find a Boss Chorus Ensemble pedal that had been stored for decades.  In the years since, many advances in computer sound modeling has made an infinite universe of tone available to the aspiring guitarist.  However, there is just ‘something’ about the Real Thing.  The owner wanted this wonderful piece of history refurbished and placed back into service.

Years of storage in the high Houston humidity has taken a toll on the outside.  What’s up with those screws on the HIGH/LOW input level switch?

Forget that stuff made in China.  This is the real thing, from Japan!

Since when was an electric guitar considered “HOUSEHOLD ELECTRONIC EQUIPMENT”?

The nomenclature for the input and output jacks appears on the top of the unit.

Let’s make a quick tour of the unit.  This is the left half of the front panel.

This is the right half of the front panel.

Several pictures of the circuit boards were made, to verify that the service literature used for this refurb matched reality.  This is the top half of the circuit board’s component side.

This is the bottom half of the component side of the circuit board.  Those fuses are on the AC output of the power transformer.

Most of the screws in the bottom of the unit were missing.  This unit was balancing on two feet.

The interior layout is actually pretty cool, well-representing the line-powered Japanese gear of the period.

I’m going back through and documenting where the various wire colors go.  Note that the wires are just tacked to brass eyelets swaged into the circuit board.  The AC power wires get their own riveted tie points.

Looking closely at the wiring.

Wiring closeups.

More wiring closeups.  This is factory wiring, I believe.

More colored wires.

The black ground wire gets its own lug.

A quick jab of the soldering iron frees the circuit board from the wiring harness.  All passive components were checked and anything that was out of spec was replaced.  Most of the forty-year-old electrolytic capacitors were replaced.

The outer jacket of the AC cord dry-rotted.  This looks gnarly, but the inner insulation seems to be fine.

A new cord is identified with the same outer diameter and wire gauge.

The blue and green wires are the input to the primary wiring of the power transformer.  Note the cable clamp pressed into service as a strain relief for the power cord.

The old cord is gone.  We can keep the cable clamp and move it to the new cord set.

This grommet would not ‘fly’ with UL today, but was fine for the 1980s.  This will be used again.

The new cord is stripped back.  Note the authentic cotton filler.

The cotton mop is trimmed away and the original cable tie is slipped on the new cord.  Next comes the grommet.

The original strain relief was retained.  The white and black wires were later terminated to the green and blue wires seen above.

Both foot switches were ruined.  Out they come!

This is the wiring side of the original ‘effect/bypass’ switch.

Out it comes.  The escutcheon is in rough shape.  Maybe we can freshen it up.

Here we’re trying to salvage some of the original hardware.  A sideways blow the old foot switch damaged the threads.

Here is the wiring side of the chorus/vibrato switch.  This switch was intermittent.

Rather than desolder the wires, I trimmed them off square.  They will be stripped and re-terminated on the new switch.

A pair of DPDT foot switches will adequately replace the foot switches in this unit.

The original trim nuts were in good shape and will be reused, to preserve the original appearance of the unit.

Now let’s move our attention to the potentiometers and switches in this unit.

The nuts were rusty but in good shape otherwise.  Here, one of my deep sockets with the felt cover is used to remove the nuts.  The felt prevents the socket from marring the soft aluminum face plate.

Note the letter “C” after the first line of text.  This denotes a reverse taper pot, used for the vibrato rate control.

Vibrato depth control is a linear taper control, thus the letter “B.”

The chorus intensity control is a linear control as well.

And who would have guessed that the level control was an audio taper potentiometer?

Each potentiomenter was flushed with Blue Shower.

A blast of Rid-Ox really does the trick on dirty contacts.

Some synthetic lubricant keeps the shaft turning smoothly.

Until I get the air compressor line plumbed to the bench, Air In A Can will have to do to dry everything out.

This process leaves everything spotless and clean, inside and out!

A soft tooth brush works well with the crinkle finish paint used on this unit.

The toothbrush cleans the grooves around the indicator lamps.

A lint-free cloth carries away four decades of gunk.

Before going further on the outside, we need to get under the front panel.

With the potentiometers and switches removed, the aluminum panel lifts right out.

Placing the aluminum panel flat on a carpeted surface, gentle pressure will allow us to remove dents.

With the front panel set aside, we can turn our attention to the power switch.  This switch needs cleaning as well.

It gets a treatment similar to the one given the potentiometers.  This is much better!

With the individual pieces reconditioned, it’s time for reassembly.

Controls and switches were installed and wired.  The wiring harness was returned to its factory layout.

We’re starting the process of restoring all the connections made by the colored wires.

Testing was performed with a sheet of cardboard between the circuit board and the metal chassis.

I spotted these parts at a local hardware store.  These screws and bumpers are perfect for replacing the rubber feet.

This guy is ready for another four decades of vintage guitar sound.  This unit sounds AMAZING!

Thanks for reading all the way through!

CONTACT – David Latchaw EE
281-636-8626

Fender Twin Custom Foot Switch Repair

Matt complained that the reverb function of his amp was erratic when he used the factory foot switch.  Could the Unbrokenstring Crew look it over and find the rat?

Let’s take a tour of the unit.  This one is in excellent shape.  Meet the ‘normal’ channel,’ on the left side.

Effects channel is in the middle.

Everything in this amp works well.  I wonder what the issue is?

Name, rank, and serial number, please!

One thing I really like about this unit is the ON and STANDBY switches sport dust boots.  Good practice to keep these switches trouble-free for years to come!

The foot pedal goes here.  This is a stereo jack, to support two functions.  Is this the problem?

Matt supplied the foot switch.  This looks as if it has never been out of the studio.

Inside the unit, we see cast frame Eminence units.  Very nice!

The tube diagram is as it should be.  I understand that the schematic is the same as the original Blackface Fender, only updated with modern components and largely built upon a printed circuit board.  Nice stuff.

No reverb here!  There is an intermittent within the pedal.

The vibrato section works fine, so we need to investigate the foot switch on the right.

Let’s verify that everything is OK here.  Very clean inside!

Amazingly, the reverb foot switch does not actuate every time it’s pressed.  A new unit is pulled from stock.

Here is the new reverb switch.  Now, the reverb is functional, but there is another source of intermittent operation.

Aha!  At the plug end, the wire insulation has pulled back, allowing the inner conductors to touch the case and each other.  This is a mess!

There are actually three conductors in the factory cable; two are used for switch functionality and the third is the braid, a ‘common’ conductor for both circuits which doubles as a ground shield as well.

Here, I’m carefully pulling one conductor out of the center of the braid while leaving the braid intact.

Here are the three ‘wires’ that we need.

I pulled the braid until it was a solid conductor.  This piece of clear tubing will insulate it from the other wires in case the insulation on the wires pulls away again.

This is the finished termination.  I had to use a big iron on the solder joint to the outer shell, and the insulation is a little worse for wear.  I’ll do better next time.  A tie wrap was added on the exiting cable to help the strain relief do its job.

Everything is back together and works per spec.

Another satisfied customer!

Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Big Muff Pi Pedal Refurb and Update

Matt owned this pedal FOREVER and needed to put it to work in the studio for a project.  But, the foot switch had disassembled itself years ago, and the audio jacks were worn out.  This pedal needed an update to the 21st century, adding compatibility with the distributed power in a pedal board.  Could the Unbrokenstring Crew make this happen?

The knobs and controls were in great shape.  Beyond the audio jacks, switching, and power, the unit works great.

With the top cover removed, we see the VERY heavy gauge frame that takes the force from the foot switch.  Yes, stomp boxes get stomped on!  The LED mounting scheme is obviously some Soviet military hardware.

The top view of the circuit board show the ‘in’ and ‘out’ jacks.  The originals are plastic and completely shelled out.

The circuit board is more Soviet military goodness.  Clearly, this board was ‘hand taped’ and not laid out with an automated.CAD program.  I’d call this ‘one step beyond hand wiring.’

Note that all the wiring insulation is white.  This harness started out as ribbon cable, and each wire was pulled out of the ribbon as it was wired to place.

A modern epoxy-sealed foot switch is trial-fitted.  This one is triple-pole double-throw on/off to handle both the required functionality of the old switch and to implement ‘true bypass’ when the effect is deselected.

Here is the user-side of the foot switch.  We need to be sure that the mushroom button is installed as high as possible to simulate the height of the old foot switch.

For those of you who know your ‘one-line’ electrical symbols, you know that these two terminals are ‘no connect.’  What?

These ‘no connect’ terminals are used to mount the current-limiting resistor for the LED.

So the current-limiting resistor is moved to its own spot in the wiring harness.  Yes, that is clear heat shrink tubing.

More ‘one-line’ electrical symbol goodness.  The body of the switch is phenolic.  It is badly cracked and ready to shatter.  Had I been able to find the missing switch hardware, this switch could not be returned to service anyway.

And for those of you who understand the Cyrillic alphabet, this pic’s for you.

The input and output jacks will be desoldered.  The gray plastic is quite brittle after all these years.

Now that they have been removed, we can complete the schematic.  Those jacks have switches in them that need to be analyzed in isolation.  The switching function is not necessarily what Western manufacturers utilize in their jacks.

The printed circuit board is temporarily reinstalled so that we can check the fit of the new jacks.

The new jacks are genuine Amphenol units, professional grade, as they say.

The terminals are bent slightly inward to clear the internals of the pedal.

The stereo jack functions as a power switch, disconnecting the ground to the 9v source when the plug is disconnected.  Both jacks need to be oriented in such a way to minimize mechanical interference with the circuit board.

The original jack escutcheons really dress up the jacks!

All new wiring was made with silver wire with a white Teflon insulation, matching the original SovTek wiring harness.

The new switch is installed.  Unlike the original foot switch, this switch is wired as ‘true bypass’ when the effect is off.

The edge of the circuit board was trimmed away to allow clearance to the body of the new Amphenol jacks.  The trace that was cut is for the sleeve terminal, which is duplicated in the array of remaining pads.

This pic shows the orientation of the notch in the circuit board to the body of the new connector.

A new 9v power jack is added between the two in/out jacks.  This jack is compatible with the ‘Boss’ pedal power “standard” with negative in the middle and 9v on the sleeve.

To reassemble the pedal, the top frame goes on first.

The cover goes on next.  This is beginning to look like a pedal again!

Matt would use the 9v power jack in the studio, but the functionality of the pedal with a 9v battery remains unchanged.

Here is a look at the finished unit, updated with steel jacks and the 9v pedal power capability.  This unit works well!

Thanks for reading all the way through!

CONTACT – David Latchaw EE
281-636-8626

 

Behringer Europower Mixer

Behringer has terminated its retail sales agreement with The Big National Retail Music Store Chain, which was probably a smart move on their part.  Fortunately, service literature from Behringer is fairly easy to obtain these days.  So, the Unbrokenstring Crew launches off into another mission sortie, this time to repair this powered mixer.

This unit needs new power FETs in the output circuit.

This unit still has a price tag on it!

Made In China pretty much tells the story these days…

I believe the date code is in the format of MMYY.

The entire power output stage is mounted on this massive aluminum heat sink.  This will be fun!

The power devices are held against the heat sink with spring tabs and screws, which can be removed with a Phillips screwdriver.

I cleaned off the conductive grease so that this thing could be handled without making much more mess than I had already made.

The discrete devices in the amplifier all test OK, so new power FETs were ordered.  These are a complimentary, matched pair of N-channel and P-channel devices.

Applying heat sink grease is logistically easier with a cotton applicator.

Both faces get a little compound.  We want complete, void-free contact between each device and the heat sink.

This is the Big Squish.

The plastic output jacks were busted up pretty badly, so new ones were installed.

The power FETs form a Class A-B push-pull stage.  Per the documentation, between five and six millivolts are measured at the test points when the idle current is correctly set.  Exercise for the Graduate Student: knowing the voltage developed across a resistor that can be easily identified on the schematic (available for download) what is the bias current?

After testing, I went back into the unit and replaced the bipolar transistors that drove the gates of the power FETs.  Now this thing really does a yeoman’s job of battling against the Silence.

Thanks for reading all the way through!

CONTACT – David Latchaw EE
281-636-8626