Carvin MTS3200 Amp Head is the Victim of Hurricane Harvey

The Unbrokenstring Crew knew that it would only be a matter of time before gear submerged in Hurricane Harvey’s floods came onto the secondary market, be it CraigsList, OfferUp, or even as used gear at a national retail music chain that I will not name here, but go by the initials “Guitar Center.”.

Who could turn down this awesome piece of gear at a great used-equipment price?  But this guy blow fuses.

 

Carvin is an excellent brand.  Their musical instruments are expertly crafted, and the electronics are top drawer.  And this amp head has three channels!

 

The rear panel of this unit shows all the versatility you could possible ask for in a tube head.

 

The select-able tetrode/pentode bias switch and a ‘cabinet-voiced’ line out signal jack are cool touches.

 

Serial number, for those who are curious.

 

The tube chart is silk-screened right on the chassis.

 

But when we open the unit up and turn it over, we see rust.  Some of the tan residue is rosin solder flux, which is OK.  But at the very top of the picture is a black pit in the end of a socket pin, which has almost entirely rusted away and will require replacement.  Most electrical component leads have a core of iron, which is then tin plated for solder-ability.  If the tin is intact, water is not an issue.  But how many component leads have literally rusted away?  Has this unit been wet?

 

The reverb tank is functional, but shows signs of water exposure.

 

These springs are very hard steel, so they rust and deteriorate very quickly.

 

Confirming our wet theory, the Tolex on the bottom of the case is coming loose.

 

Did I remove those screws and not notice the rust?

 

Looking closely at the hold-down clips for the tubes, they are completely rusted.

 

The steel chassis is coated in white enamel, which is really Top Drawer.  But receding flood waters left mud.

 

Tear-down is in order to assess the condition of the unit.

 

Everything has been wet.

 

This is the component side of the circuit board that holds the power tube sockets.  All this crusty solder flux tells me that the rosin is ‘activated’ with phosphorus, a Good Thing to make good solder joints, but a Bad Thing if it gets wet.

 

The preamp tube sockets show the same reaction with the phosphorus.  This will all need to be cleaned and reworked.  Some of these leads are completely hollow as the iron core has rusted away.  It will be better to replace the sockets.

 

Electrical problems around the circuit board caused the preamp tube on the left to overheat.

A complete overhaul and rebuild of this unit would be necessary to restore functionality and reliability.  Most components should be replaced, including sockets and connectors.  However, the customer purchased this amp because it was in his price range.  The repair quotation was not in his price range.

If you are shopping for gear and see signs of water damage, such as loose Tolex, rusty hardware, or dried dirt where it shouldn’t be, you should consider having a tech go over the equipment to assess the condition and find potential reliability problems before you buy.  Rusty transformer laminations are particularly troublesome, as the rust pierces the insulating coating between laminations and allows eddy currents to flow, potentially overheating the transformer.  Transformers are expensive to replace.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Epiphone PR-5E Acoustic Gets New Electronics

This wonderful instrument was rescued from an abandoned house.  It sounded good acoustically, so the new owner asked if the Unbrokenstring Crew could repair the electronics and get it playable again?  Let’s get to work!

This instrument is only a few years old, purchased and then cast aside.

 

An online source for specialty guitar parts had a 2018 model of the electronics.  Can we make it work?

 

The mounting scheme uses four screws in the corners.  Cleats will be added to the guitar so that the screws hold.

 

But the REAL advantage of the 2018 electronics is that the enclosure matches the curve of the body.

 

Common wood items such as yard sticks, tongue depressors, popsicle sticks, and paint stirrers are made from birch, the straight-grained ‘poor relation’ to maple.  So the paint department lady at Home Depot gave me this stirrer.

 

Cleats to tightly hold the electronics in the body are fabricated by hand.

 

Next, the cleats are sanded to fit the curve of the body on the inside of the bout.

 

These are ready to trial-fit.  The bevel on the corner, lower-left side, clears an internal brace in the guitar.

 

One shim goes here.  Note the angled pieces, which will catch the screws in the electronics.

 

To protect the finish, low tack painter’s tape is used all around.

 

These clamps will hold the cleats in place as the hide glue sets up.

 

Both cleats are installed and the hide glue is curing.

 

Additional reinforcement is added in the corners to give the screws more material to grip.  These bits will be in compression, so they don’t need to be super-strong, only tough.

 

Before we get too far, we need to do another trial fit.

 

I think we’re going to be good here!

 

I will pre-drill the holes where the screws will be installed.  This should minimize splitting of the small cleats.

 

The actual drilling will be finger-powered, using this pin vise.

 

All four holes are pre-drilled.

 

Yes, I know.  This isn’t terribly interesting.

 

The screws are installed.  Not bad!

 

The jack plate holds the battery and has both 1/4th inch phone plug and balanced XLR connections.  It was temporarily removed to give more access to the interior of the instrument.  The new electronics hook right up to the jack plate.

 

This is a new one on me.  This battery was in the guitar when it came in.  The Golden Thumbs-Up Emoji Award!

 

And, while we’re here, we’ll clean the instrument, string it, and do a setup.

 

The electronics come alive!

 

This is a cool tuner.  The LCD screen has a pointer that swings across its face.

 

Beauty is skin-deep, but what really counts is just below the surface.  This rescued guitar is ready to make music!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

TC Helicon VoiceLive3 Pedal Refurbishment

A lot of capable technology lives in this device.  However, if the musician can’t select a configuration because the big rotary selector knob broke off, then it’s e-waste.  Can the Unbrokenstring Crew bring this pedal back from the dumpster?

Pedals live on the floor, and there is plenty of dust to attest to to the fact that this unit has been working hard exactly where it was born to be.  No harm in cleaning and detailing this unit before we’re through!

 

The main issue here is the broken rotary encoder.  We have the knob, but not the shaft.

 

Time for a quick tour before we begin.  This pedal serves both vocal and instrument duties.  Flexible monitoring options are available, as well as 3.5mm stereo headphones out and line-in capability.

 

Separate paths are maintained through the unit for vocal and instrument signals.  Stereo effects are available.

 

Midi, USB in and out, and a power switch complete the rear panel.  That black rectangle above the USB ports is a cleat to tie off the power cord, to make it a little more difficult to pull the barrel plug out of the power jack.

 

It takes a lot to get into this box.  Let’s start at the bottom.

 

The bottom lid is off.  So far, so good.

 

The footswitches are VERY old school, rugged American made switches, proven reliable since the middle of the century.

 

Let’s remove the sides next.  This bracket on the side panel supports the bottom circuit board.

 

These are the external screws on the sides.

 

These are Torx-head cap screws, giving the device a cachet of ‘tamper-proof-ness’ unless you have the right tools.

 

Next, the rear panel comes off.  More Torx screws.

 

Under the side plates, metal plates support the unit to make a very strong metal box surrounding everything.

 

At last, we can get to the next layer.  The unit is still upside down.

 

I’m documenting where cables go.  This is a front-panel indicator assembly.

 

More cable documentation.  See the Ruffles potato chip?

 

Most of these cables will be marked with a Magic Marker to identify them for reassembly.

 

Next, the front panel is removed.  These knobs pull off.

 

There are no lock nuts under these controls.  Interesting…

 

We have a few more screws to keep track of.  Many of these are a certain length, and shall be returned to the right place.

 

The LCD is tilted back to gain access to a few more Torx cap screws.  Our final objective is in sight!

 

The broken rotary encoder is on the same circuit board as the LCD.  To minimize stress on the circuit board, the old rotary switch is cut away, leaving the individual leads in place.  These individual leads are much easier to de-solder.

 

The holes where the new encoder goes are cleaned and ready to go.

 

This rotary encoder is a special order part.  Not just any component will fit.

 

This is a workmanship check of the solder-side of the rotary encoder.

 

And here is the component side.  Again, not just any part will work here.

 

We can take a break and do the clean-up prior to reassembly.  Compare this with the first picture.  Yes, the LCD window has been cleaned and polished.

 

Reassembly is the reverse of assembly (wow, that’s profound.)  The correct fasteners must be reinstalled at each step.

 

Everything is back where it belongs.  Remember the Ruffles potato chip?  That is actually a dab of adhesive that secures the flat ribbon cable.  A dab of silicone will be added in a moment to secure the ribbon cable again to the same spot.

 

Looking good!  Everything initialized.  The factory reset procedure is complete.

 

Somehow, I thought that this was an appropriate preset screen to display.  I think we’re done!

 

Here is a video showing how the rotary encoder works to change presets and configure the unit into different operating modes.

Support this band! – Fake Believe

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Mackie Thump Active Loudspeakers Need Tweeters

Two active loudspeakers have the same problem – the high-frequency driver has quit.  Does the Unbrokenstring Crew have what it takes to get into these loudspeakers and do the repair?

The enclosures of these units are molded from a very durable plastic material.

 

So are we dancing?

 

The rear panel has a crossover frequency control, equalization, overall volume, and audio inputs.

 

The bottom of the real panel has an input power IEC jack and an on/off switch.

 

The ‘Suggested EQ Settings’ suggests to me that this is a little more consumer than pro.

 

Perhaps we can gain access to what’s wrong by removing the loudspeaker.  These nice Allen-head machine screws hold the loudspeaker frame to the case.

 

With the loudspeaker out of the way, we realize that we cannot really get any tools inside to replace the high frequency driver.  We will need to split the case apart, which is no big deal but at least thirty screws are used!  Let’s get the electric screw driver warmed up and get to work.

 

The first thing to remove is the handles.  This flat-head screw comes out with the aid of a magnet.

 

Inside the handle, a nut falls out when the screw is removed.  I’ve retrieved the nut with a magnet.

 

The nut is held in place in this molded socket.  This may be interesting to reassemble.

 

This one foot long screw driver bit will allow us to reach all of the screws.

 

Some of the screws are long.

 

Some of the screws are shorter.  We make note where they all go.

 

Here is the foot-long screw driver bit at work.

 

There are screws holding the case halves together underneath the plate of the amplifier.  Off it comes!

 

More screws come out.  Glad I got this long bit!

 

The plate that the amplifier is mounted on is gasketed in place with this L-shaped plastic strip on two sides.

 

At last, we are in!  The two sections of the enclosure come apart.

 

And here is the high frequency driver that needs replacement.

 

To completely separate the two halves of the case, this cable to the pilot light can be removed.

 

These drivers are held in place with four screws.

 

Interestingly, the voice coil inside the driver is intact, yet the unit did not work.  This tells us that the voice coil had separated from the diaphragm.

 

The exact replacement, like the original unit, is made in China.

 

The new driver is installed with four screws.

 

All of those screws go back in where they came from.

 

And there are a lot of screws!

 

I used blue tape to keep the nuts captive while the handles were reinstalled.

The handle screws are easily tightened as the nuts are held captive in the plastic socket.

 

Now that the handles are tightened down, the blue tape keeping the nuts in place can be removed.

 

A little originality is necessary to finish the job.

 

At last, these units are ready for testing and return to service!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Intermittent Fender Acoustasonic 150

A fellow musician gave Charles this amp, which was nice gesture.  However, the friend said that it was intermittent.  Could the Unbrokenstring Crew turn this gesture into a reliable amp?

Styled as a unit from the Fender Brownface era, the exterior certainly checks all the boxes for Brownface goodness, with the Correct knobs and silk-screened front panel true to the archetype.  One channel is reserved for an instrument, and the other channel is tailored to vocal performance, including a dual XLR/quarter inch jack for a microphone.

 

No metal shredders allowed.  This unit has a tweeter, and an electronic gain structure that does not distort.  Just the thing for Charles’ acoustic act.  This badge still has the protective plastic in place.

 

The speaker cabinet is sealed.  This polarized connector keeps three pairs of audio signals from the amp going to the correct loudspeaker and tweeter.

 

On the back side, we find the ON/OFF switch and the IEC power socket.  Most of the rear panel is slotted for ventilation.

 

This is a solid state unit, with plenty of pep to be loud.

 

The internal architecture permits stereo operation, as is shown by the FX loop connections.  I did not play around with the USB functionality, but it’s in the manual.  We have bigger fish to fry.

 

Name, rank, and serial number, please.

 

This circuit board holds all the connectors for Line Out and effects loop functionality, as seen on the rear panel.

 

This assembly is an AC to DC power supply on the left, and an efficient Class D audio amplifier on the right.

 

Digital signal processing (DSP) is used to create the reverb and other effects.  The DSP functions are on the mezzanine board on the left.  The thin white cable in the center is the USB cable.  The main printed circuit board handles the clean audio chain and the connections to the front panel controls.  The flat cable on the right brings power from the AC to DC board and sends audio to the amplifier.

A lot of surface-mount components are found in this unit.  Those little cans are electrolytic capacitors; black squares are integrated circuits.  Each of those little black squares does the job of two vacuum tubes.  I feel old and obsolete.

 

The check mark probably means that someone tested this at the factory, I guess.

 

So the audio processing hardware is seen at the top of the picture and the power stuff is at the bottom.

 

The AC wiring comes from the switch directly to the circuit board, where there are filters and a fuse.

 

This power stuff is actually a switching power supply, which efficiently creates the various operating voltages.

 

If you look closely at the gold rings on the circuit board, you will see solder that looks ‘strange.’  It does.  Gold atoms mix into the molten tin/lead alloy while the solder joint is in the liquid state.  The gold makes the solder brittle.

 

The entire circuit board is gold plated.  This plating is among the flattest finishes available for bare circuit boards, perfect for surface mount technology (SMT) components but is a metallurgical compromise for thru-hole components..

 

As you can see, for thru-hole technology components such as these pins sticking through the board, the results of the soldering action can leave something to be desired.  Do you see the holes in the solder joints?

 

Now that those holes are fixed, we can focus on the real source of the intermittent operation.  Do you see that light blue resistor with two red stripes hiding behind the capacitor and the heat sink?

 

That light blue resistor was soldered here.  Or to be more precise, it was soldered there at one time.  The cracked solder joints became intermittent conductors.  Here I have removed the resistor and cleaned away the old solder in preparation for making a new pair of solder joints, free of gold contamination.

 

Another issue with this amp is that someone has been playing with the loudspeakers.

 

This loudspeaker fits the cabinet perfectly, but electrically, it is a 40 ohm (yes, forty ohm) loudspeaker, designed for use in a public address paging system (you know, that mess that you hear at the doctor’s office playing MUZAK, mercifully interrupted by an announcement for someone to call a telephone extension?  Yeah, that.)

 

The Correct part is available.

 

Who would have thought that you could actually replace a bad loudspeaker with a new one of the correct type?

 

Do you like those TV shows where they have a build-up to the ‘Big Reveal’?  I don’t either.

 

Fortunately, we have the correct part and are ready to install it.

 

Once we replace the grille, you will never know the difference.

 

See, I told you that you couldn’t tell the difference.  This unit plays beautiful music and the functionality is solid.

 

Support this musician, winner of a Texas Music Magazine 2018 Album of the Year:  http://www.charlesbryantmusic.com/

 

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

 

Rickenbacker Rick-O-Sound Bass Repair

Craig is a Ric Man.  This beautiful blue bass in only one of his many Rics.  This one has problems with getting both pickups to work.  Could the Unbrokenstring Crew get all this sorted out?

This instrument plays beautifully and has no real discernable setup issues.  However, the wiring seems to be amiss!

 

More than a few of you will have heart palpitations seeing this head stock.

 

Two output jacks allow a mono mix of both pickups as is usually found with most multi-pickup instruments, plus a special “Ric-O-Sound” jack that presents the signals from two pickups as two separated signals, accessible with a stereo cable (TRS.)  This gives the player the ability to run two preamps, two effect loops, two separate amps, etc.

 

Immediately after looking under the pick guard, we find a loose wire.  Poor soldering here.

 

This isn’t even tinned.

 

Here is another broken wire, another ground wire.

 

We have a stack of three inside-tooth lock-washers under each output connector.  Not much spring action available from the teeth of these locking washers, so they don’t really lock.

 

A magnet is the quickest way to clear all this extra hardware out of the control route.

 

This is the stereo jack handling the “Ric-O-Sound” duties.

 

The mono jack handles the single-ended output from this instrument.

 

Soldering workmanship on the switch needs some attention as well.

 

Disconnecting each pickup allows us to do some cleanup in the wiring cavity.  The neck pickup is ohmed-out.  The neck pickup is sometimes called the ‘treble’ pickup.

 

And we do the same with the bridge pickup.  This pickup is also called the ‘bass’ pickup, which seems redundant.

 

Perhaps this soldering was done with plumber’s solder.  It is awfully dull.

 

Another look at the switch.  Not much to brag about here.

 

The ground connection to the control is redone.  Smooth and shiny is the name of the game when soldering.

 

I labelled the controls BV (Bass Volume,) TV (Treble Volume,) BT (Bass Tone,) and TT (Treble Tone.)

 

Now that the controls are identified, we can install the knobs in the Correct location.  Yes, they were in the wrong place.

 

Earlier I pointed out the stack of three inside-tooth lock washers.  Here’s why I mentioned it:

 

When stacked, the teeth have nothing to push against.  The teeth are literally hanging out in space.

 

A flat washer in the middle will provide some ‘resistance’ for all the teeth to press against, thus restoring the action of the lock washers to that of being, er, well, lock washers.

 

The jacks are Imperial measurement and this washer must have been metric.  A little gun-smithing is in order.

 

The output jacks are wired and tightened into their correct locations.

 

Testing shows no output.  It has something to do with this volume pot.  What the hey??

 

This is the hey.  This bit of conductive solder debris was underneath the volume pot, shorting the ‘stapled’ contacts seen in the previous picture to each other, and thus, shorting the output to ground.

 

Together again, and it’s playing in stereo!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Ampeg B2-RE Bass Amp Gets New EQ Potentiometers

Bass players use SERIOUS hardware, and this Ampeg B2-RE is a serious, heavy, high-end bass amp.  So why in the world does Ampeg use those tiny little plastic slide pots for the equalizer controls?  The Unbrokenstring Crew digs in.

Ampeg is a name that needs no introduction nor elaboration.

 

Three of the plastic handles are broken off.

 

A tour of the rear panel shows the cooling fan, the quarter-inch speaker jacks and Neutrik jacks for output power.

 

The preamp and power amp can be separated using these jacks,  An effects loop is nice, and a balanced output for the poor sot in the control room is a nice touch.  The balanced output has a switchable attenuator.

 

A look inside shows a big green circuit board that handles the power amp duties.  This view is dominated by the toroidal power transformer on the right.  The ribbon cable on the left carries power to and signals from the preamp board.

 

And here is the preamp board.  Interesting, the slice potentiometers for the EQ are located on their own circuit board on the left side of this picture.

 

The preamp board needs to come out to get to the slide pots.  This end of the cable comes loose easily.

 

Screws hold the preamp board in place in the chassis.

 

All the knobs come off, as well as the nuts beneath them.

 

The input jack has its own nut and washer.

 

While we’re here, an inspection of the unit reveals a solder joint on the path to failing.  This is an easy fix.

 

The slide potentiometers used by Ampeg are special for a couple of reasons.  One reason is, they have this nice vinyl flap over the slot that helps keep dust out of the internals of the potentiometer.

 

The potentiometer board is held down with these screws and brackets.  This needs to come apart next.

 

The other thing that makes these slide potentiometers special is that they use three legs to attach to the circuit board.

 

Here is the exact part number that needs to be specified when purchasing replacements.

 

A similar part is available from other sources, but if you look closely, the ‘pin-out’ does not match.  The correct part is in the foreground, and the ‘new’ incompatible part is seen in the background, with the ‘1736’ marking, which is probably a date code of year = 2017 week = 36.

 

I was curious if the slider and handle could be removed from the new parts and substituted into the old pots.

 

The interior view of the slide pot.  The black plastic thingie with the fingers, on the left, is the wiper, and the black strip on the right is the resistive element.  The fingers slide along the resistive element to achieve the variable resistor function.

 

Oh, drat.  The sliders are a different thickness.  We won’t be able to use the new parts to repair the old controls.

 

So, a week later, a batch of the new controls come in.  We are going to change them all out.

 

What do you think, folks?  Should I clean up the front panel and remove all these presets?

 

The new parts are installed.

 

The workmanship appears to be pretty good, if I do say so myself!

 

Back on the air, this Ampeg is ready to really rumble through its four hour burn-in!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Boss BCB-60 Pedal Board Repair

This pedal board quit completely during the church service.  Joe got it going again by rewiring around everything after he realized that the power supplied from this pedal board died.  Could the Unbrokenstring Crew get to the bottom of this issue?

Joe has his name on everything!  This pedal board is actually a big rugged tool case, with a self-contained power supply for all the pedals.  Velcro holds everything in place.  As this problem did not actually involve any pedals, they were removed before we got this unit to repair.

 

This is the model number.

 

This is the serial number.

 

Company name and nation of origin.  Not China!  (Yes, I am one of those people.)

 

This panel distributes audio and power in and out.  When power is applied, there is no power out.

 

This is a closeup of that panel.  HINT: You can use any 9v negative center power source, with sufficient capacity.

 

Audio jacks are on the right, and power is on the left.  This whole assembly is wired like a loop-back panel.’

 

Removing the connectors allows full access to the circuit boards.

 

Interestingly, the middle board shares power.and audio.  See the diode?

 

Examination of the solder joints reveal excellent workmanship.

 

This diode on the center board is a anti-polarity-reversal diode.  This prevents bad power from reaching the pedals.  When this diode has failed open-circuit, it prevents ANY power from reaching the pedals.

 

This diode is equal or better than the original part and is the highest-spec’d part that would fit on the board.

 

Reassembly is the reverse of disassembly.

 

Audio and power functions are now completely restored!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Peavey MKIII Bass Head Needs Un-Smoked

This solid state Peavey Bass head is also capable of handling mixer, equalization, and preamp roles for public address, monitor, and other sound reinforcement roles.  But power amp quit!  Can the Unbrokenstring Crew help?

The AutoMix function that Peavey developed has been discussed elsewhere in the blog.  Lots of EQ knobs here!

 

Note the graphical EQ and bi-amp capability.

 

Woah!  An Instrument System!  Ooh.  Aah.

 

On the rear panel is the power switch and speaker connections.

 

Peavey mixes and matches front panels (inputs, preamp, eq) and rear panels (ps, power amp) to build different heads.

 

As is the case with many pieces of electronics, the City of Los Angeles Fire Department approves this unit!

 

Name, rank, and serial number, please.

 

The blue circuit board at the top is for connections to the power transistors.  The I/O connections are to the left and the power supply filter caps are seen here.

 

More blue boards at the top, for power transistors.  Driver transistors are found on the square heat sinks.  Do you see the problem yet?

 

This circuitry is all preamp and tone circuitry.

 

This sucker got HOT!

 

The worst damage was to components that were near the root cause.  They burned because the transistor on the aluminum heat sink suffered an internal short circuit.

 

The heat of the electrical fault was high enough to melt solder, which happens around 650 deg. F.

 

A matched set of driver transistors were installed and the circuit board cleaned.  The destroyed components to the right have been removed and will be replaced.

 

The new parts are mounted just above the circuit board.  We can get flame-proof resistors now, unlike when the unit was built with in the 1970s.

 

More collateral damage was found on one of the blue boards.  This solder trace acted as a fuse at its narrowest point.

 

The circuit board is now cleaned up and the gap is bridged with a bit of 16awg solid copper wire.

 

Some of the power transistors were shorted as well, so all of them are now replaced with a matched set of eight.

 

These parts are still made by ON Semiconductor, the heir apparent to the Motorola semiconductor product line.

 

The electronics are back together.  The filter capacitors are original, but are still in great shape, so they remain in service.

 

And, of course, after all the components and circuit boards are in flames, the fuse finally does its job.  Of course.

 

With a new fuse, the electronics are connected again and initial tests begin!

 

This unit is back on the air!  This unit is almost hifi sound quality, with endless bottom end.  Good Job Peavey!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Warmoth FrankenCaster: It Lives!

This offset-waist project guitar is playable and is actually very cool.  The owner had ‘gotten in over his head’ and broken a few screws and buggered a few others.  Could the Unbrokenstring Crew whip this instrument into shape again?

The easy part is to install gold Gibson speed knobs on the controls.  There are a lot of good parts in this instrument.

 

Looking more closely, the neck pocket will need some serious attention.  What’s going on here?

 

This is what’s going on.  If you look at the high and low strings, you will see that they are not the same distance from the edge of the fret board.  This neck is not lined up with the body of the guitar.

 

It is easy to remove the truss rod cover because these screw heads are already sheared off.

 

The heads of the screws around this pickup were mangled to the point that a regular Phillips screw driver would not engage them anymore.  Here we’re using a pair of cutters to twist the screw out while a magnet serves as a sentinel to keep pieces of metal that will inevitably shave off the screw head away from the magnet in the neck pickup.

 

Wow these are long.  These go most of the way through the body.

 

We are still working on this one.  This is really tough.

 

Note that the head is chewed up pretty badly.  New screws are already in stock.

 

No springs or tubing are underneath this pickup, bur rather a chunk of too-thick too-hard foam.

 

Now we know where this body came from!

 

And the neck is from Guitar Fetish.  Here, I marked where the body ends with a dotted line.  More on this later.

 

So what can we do about these broken screws?

 

No problems removing the tuners…  these screws were busted off as well.

 

To remove the broken screws, we apply heat to the body of the screw.  This dries out the surrounding wood so that it shrinks slightly.

 

I used the same technique with the wire cutters to grasp the body of the broken screw to twist it out easily.

 

Rinse and repeat for the remaining broken screws.

 

Now that everything is apart, I need to fix this neck pocket.  First, we get the bottom flat.

 

Then we get the sides flat.  This body was painted after it left the factory, so we have plenty of over-spray in the neck pocket that we need to clear out with this scraper.

 

I believe that we are down to real wood again.

 

Acoustic coupling occurs best when the neck and body fit tightly, ‘bone on bone,’ if possible.  I really like this wood hardener, which is essentially solid Lexan dissolved in a light solvent.

 

This raw wood will take a few coats to seal and harden.

 

As the old cowboy on the cattle drive once said, “Be sure to look back to see if the herd is still behind you.”  Periodic fit checks are always a good idea.

 

This neck is beautiful because of the thick layer(s) of polyurethane finish.  However, the polyurethane layer may get in the way of acoustically coupling the neck to the body.  Here, I’m hatching the area where I will scrape away finish.

 

Again, the luthiers’ scraper is the perfect tool for removing finish evenly and smoothly, leaving the surface exactly flat.

 

That is much better!  Not shown: the finish on the end and sides of the neck where it meets the body is also removed.

 

A pin vise holds the proper-sized twist drill to resize these holes for the Correct pickup screws.

 

A little canned air clears out the cuttings from the holes.

 

Over-sized screws held the pick guard in place.  The Correct screws are smaller.  Here, a small dowel is glued into each hole, which will be re-drilled with the proper-sized hole.  This is hide glue shown here; just fine for this duty.

 

Once the hide glue is cured, each dowel is trimmed flush.

 

I jumped ahead to show how the Correct screws are nearly flush with the top of the pick guard.  Almost factory.

 

This single-coil pickup reads as an open circuit.  That tiny wire is broken.

 

The tiny wire is broken because these black and white leads can twist around.  Hot-glue now holds them stationary.

 

The pickup is working now.  Here is some new, softer foam in place to hold the pickup in position.  Leo Fender would have used short pieces of vinyl tubing on the screws to act as a spring, but these covers go all the way to the bottom of the cavity route, so the foam is the best option for this setup.  Oh, and you can’t see it, but the copper pulled out when the original foam was replaced, so this guitar has copper in the pickup route and under the pick guard.

 

Here is the actual pickup.

 

And here is the separate cover.

 

The Correct screws are not nearly as hard to drive as the other screws.

 

More Guitar Fetish goodness!  The metal parts of the guitar should be tied to a single point, not at various places along the signal path.  This soldered wire ties the metal body of the pickup to one side of the audio path, and has got to go.

 

That connection is now cut open.

 

A separate layer of foil is wired to the single point ground.  The connection to the bridge and strings is accomplished with another sheet of foil and this outside-star lock washer.  Again, the mechanical ground is not part of the signal path.

 

Everything goes together as it should.  See how the star washer makes the connection between the bridge and foil?

 

The Correct controls are marked T for tone and V for volume.  The switch is ready to wire.

 

The new wiring is accomplished with solid wire in Teflon tubing.  The pickup wiring is the vintage ‘push-back’ wire, which is actually really easy to use and can be very clean-looking as the insulation is cut without resorting to wire strippers.

 

When the control plate is in the correct position, new holes are bored for the screws.

 

The neck plate needs some attention.  This metal polishing paste is also what I use to polish fret wire.

 

These holes are reamed to the proper size for the Correct screws.

 

The tuners are going on!  A bit of red felt is glued to the face of the socket so that the finish is not marred.

 

These new screws going into the correctly-sized holes are very well-behaved now.

 

The truss rod cover screws will now live in properly-sized holes as well.  The pin vise is getting a workout today!

 

The customer uses these strings.  We need the guitar strung so that we can get the neck straight.

 

Note that the outside E strings are equidistant from the edge of the fret board.  The screws attaching the neck to the body are tightened at this point.

 

Now that the neck is properly positioned, we can finish the setup.  The truss rod is adjusted to make the neck perfectly straight.  Do you see the slip of paper next to fret 9?  It is used as a feeler to see that the ruler is in contact with the fret board all along the neck.  A piece of paper is about 0.0015 inch thick or so.  It is used to check for fit between every fret on the fret board.  Yes, that makes a difference!

 

This neck is brand new, and so the frets had never been leveled.  Just a tiny bit of sanding was all it took.

 

Here I am taking a measurement of fret wire height.  I need this shortly to file the nut slots.

 

Frets are polished.

 

Fret board is cleaned and conditioned with oil.

 

Here we are cutting the nut slots to depth (about 0.006 inch plus the fret wire height measurement made earlier.)

 

Once the nut slots are at the right depth, the rest of the nut is sanded away to make the slots shallow.  We need to sand a little bit more away near the high E and B strings, and maybe next to the D string.  We’re getting there!

 

The instrument is back together and sounding good!

 

This is a closeup of the saddle barrels.  These are factory intonated and are VERY close to correct.  How do they do that?

 

Our patient is making her debut at the studio.

 

First Note.

 

I think he likes it!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626