Professional Advice for Those Caring For Flood-Damaged Guitars

Roy Bowen and Scott Leedy of RS Guitarworks in Winchester, Kentucky had it in their hearts to reach out to Houston area musicians, documenting their experiences gained while working with flood-damaged guitars during the big flood in Nashville back in 2010.  The Unbrokenstring Crew is honored and blessed to be able to publish this document for your edification.  This supplements my previous post, which was general in nature and included electronics.  To wit:

 

Guitar Flood Triage

Below is a list of steps that we developed while restoring guitars from the Nashville flood and Hurricane Sandy.  The following steps should be taken as soon as possible.

 

  • First remove strings.

 

  • If truss rod is not removable, loosen truss rod ½ turn, add a couple of drops of penetrating oil on the threads then tighten ¼ turn.  On vintage Fender or Gibson guitars where the truss rod can be removed, remove truss rod lug. Oil the threads then re-install snug but not tight.  You want to make sure threads are lubed so the truss rod does not rust in place.

 

  • Remove all parts from body including hardware and electronics.  Wood will try to move and solid items like screws & tuners will not let it move.  This can cause cracking of the wood, as well as cause rust staining in the wood.

 

  • On bolt on instruments remove the neck.

 

  • Take all hardware and place it in bags filled with uncooked rice and leave it until you are ready to re-assemble.

 

  • All electronic parts such as pots and switches should be cleaned with a quality electronics cleaner and then stored in uncooked rice as well.

 

  • Air-drying of the wood is best after parts have been hand dried inside and out.  Keeping guitars in a small room with a dehumidifier can also help.

 

  • Do not try to use any cleaners on the finish or hardware of the guitar until it is properly dried and stabilized.

 

  • Do not try to tape down loose binding or wood coming un-glued as it may damage fragile finish loosened by water

 

  • Get the guitar to a qualified repairman as soon as possible.

 

Be sure to visit http://www.rsguitarworks.net to tell them THANKS and to check out their restoration work with other water-damaged guitars.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Some Advice for Musicians Whose Gear Was Water-Damaged by Hurricane Harvey

Shortly after the Shuttle Explosion in 1986, the computers onboard the Challenger orbiter were retrieved from the floor of the Atlantic Ocean.  Each ‘set’ of boxes was sent to a different NASA Center for analysis.  One set came into the IBM Federal Systems lab in Clear Lake, Texas, where we dried, partially disassembled, and reassembled the hardware in hopes of recovering any clues regarding the accident.  I was the sub-contract manager at IBM at the time and was tasked with engineering support for the effort, including electrical test, micro-soldering, cable assembly, and such.  I am proud to report that the unit came back to life after two weeks of salt water immersion, and the data in the memory core was intact up to the point that vehicle power was lost; That information contributed greatly to the accident timeline.

So I want to weigh in on some strategies for musicians who found that their gear was water-damaged in Hurricane Harvey, which is still affecting Coastal Texas as I write this.  Let’s get going!

  1. Don’t turn anything on to see if it still works.  Odds are, it won’t.  And it won’t because you turned it on, dumbass.
  2. Unplug everything.  Your power is probably off anyway, but it never hurts to be sure.
  3. Remove ALL the batteries.  This includes tuners of all kinds, even the ones built into an acoustic guitar, guitar pedals and effect units, portable recorders, laptops, microphones, everything.  Same process as when your cell phone falls in the toilet.
  4. For all stringed instruments, slack the strings.  You don’t have to remove them, but just remove the tension.  Loosen the pegs on your violins/violas/cellos/basses to slack the strings; don’t bother with the fine tuners.
  5. For instruments with truss rods in the neck (guitars, basses, etc.) slack the truss rod.  Just a half a turn in the direction of ‘more loose, not more tight’ is the way to go.  For most instruments, that’s counter-clockwise.
  6. Drum heads on banjos and drum kits should be slacked as well, if the shell was wet.
  7. Many woodwinds will be OK if you were treating them with sweet oil on a regular basis.  The case will be in worse shape than the instrument.  Wipe everything with a dry towel and let it air dry for a week or two.  Inspect any pads and remove the reed; the reed will need to be replaced anyway unless you use synthetic reeds.

Now that everything is stable, let’s consider the recovery options.  The challenges we face are as follows:

  • Acoustic instruments made of wood are not damaged by a little water.  A lot of water will swell the wood and stress/break the glue bonds.  The sooner the liquid water is removed from the surface of the wood, the sooner we can begin the process of drying the instrument.  Wipe it down with a dry towel, inside and out.  There are instances of classical guitars stored in a basement in Central Europe that had absorbed TWICE THEIR WEIGHT in water that were successfully dried and returned to play-able condition.
  • Acoustic instruments made of wood ARE damaged by too much drying.  Shrinkage causes the wood to pull away from glue bonds and pull away from itself e.g. crack.  This Peavey neck became over-dried in hot attic:Fortunately, we have (and will continue to have) PLENTY of humidity so a good, slow, open-air drying over the next couple of weeks will cause the least damage to our acoustic instruments.  Resist the urge to pull out the hair dryer!
  • Solid body instruments are, more impervious to liquid water by virtue of the fact that they are usually finished in polyurethane or other rugged finish.  Again, wipe it down with a dry towel.  We’ll come back to work on the controls in a moment.
  • Martin guitars with the composite bodies, and Ovation guitars with their famous ‘bowls’ may be difficult to recover.  The sound board expands and shrinks at a different rate than the rest of the guitar.  Ovation will (upon request and sufficient $$) replace a wet top with a new one.  The Music Factory in Pearland has done this with a few of their new Ovations following the last hurricane.  I have not spoken with Martin but my guess is, you might have to call them and discuss the options.  Many of the composite/laminate guitars are under $500 which limits the range of repair options.

The areas of concern with our electronics fall into these categories: (1) cabinets and grille  (2) loudspeaker cones  (3) controls and switches.

Note that I did not say anything about the electronics themselves.  Electronic assemblies built after, say, about 1990, are mass produced by a process that uses water as a cleaning solvent.  This is called ‘aqueous cleanup’ and is almost ubiquitous in all electronic assembly shops around the world.  Your electronics will fare fare better in the flood than you think, particularly if we don’t energize them while wet.

  1. Let’s start on the cabinets and grilles.  Remove the grille and dry what you can with a towel.  The frame is almost always wood, and the fabric is almost always a synthetic.  The wood should be allowed to dry slowly over the next couple of weeks.  Do not apply any heat.  The frame may still warp a little, but we will deal with that when we reassemble the cab.
  2. Wipe all water from the cabinet, paying particular attention to the inside and bottom of the cabinet.  Remove the reverb tank, if it is present, and set aside.  Again, with the cabinet, a slow dry may be all it needs.  If the cabinet is made from particle board, you will see swelling which may spoil the appearance of the unit.  The particle board will never be as strong as it was before it got wet.  If your cabinet is particle board, you might convince yourself that Harvey has given you permission for an upgrade to a pine or plywood cabinet.
  3. Carefully remove any remaining liquid water from loudspeaker cones.  Let everything dry out for a week or two.  Then GENTLY push the cone evenly forward and back and listen for any rubbing or scratching noises.  If you don’t hear any noise (called ‘motor noise’) you may be OK.  Unfortunately, some magnets have a high concentration of metallic iron, which will rust (and swell) in the presence of moisture.  If the rusting is bad enough, the loudspeaker needs to be reconed or replaced.

Let’s take a look at the electronics.  The controls and switches on guitars and the controls and switches on amplifiers are treated in a similar manner.  Circuit boards and wiring harnesses are not hard to clean up if you are handy.  If you are comfortable disassembling your amp head or accessory, then Read On.  If not, there are many shops (not just mine) that are on Facebook that are competent to perform these repairs.  I am detailing these procedures so that the do-it-yourself-er can have some confidence to proceed, and also so that the non-do-it-yourself-er can speak competently with your chosen tech.

  • Compressed air is your friend.  The air blast will remove any liquid water present.  After disassembling your gear, get compressed air underneath components, connectors, transformers, anywhere there is a place where water can reside.  Those little cans of ‘electronic dusters’ are cool but expensive.  Pull out the air compressor.  Pull the bottom plate off your pedals to gain access to anywhere water may be lurking.  Remove those pick guards and blow everything dry.  Open up those battery boxes (you did remove the batteries, didn’t you?)  Dry everything!
  • Switches need a rinse and then lubrication.  I use ‘Blue Shower’ as a rinse, which is for cleaning television tuners.  There are other products that work as well.  Google “CAIG” read up, and go shopping at Fry’s for some of the CAIG products they carry.  Start with the CAIG F5 stuff as a rinse, then the CAIG GOLD stuff as a protector lubricant.  I use the CAIG GOLD product as well as some MIL-SPEC stuff (because I Am Cooler than you and can get MIL-SPEC stuff and you can’t.)
  • Hit the input and output jacks with a little CAIG GOLD on a cotton swab.  This is just good routine maintenance, and is particularly vital now that your instrument may have been wet.
  • For controls that were working fine before the flood, I would just use a shot of the CAIG Fader Lube (same aisle at Fry’s) as a water displacer and a lubricant.  Don’t try to rinse good controls because you may displace the factory lubricant and put it where it may create noise on the resistive element.  Keep It Simple.
  • Cables may be problematic.  My advice would be to toss the wet ones and get new ones.  My reasoning is this: Cables are often the weak link in any setup, even when new.  You know this.  Water will deteriorate cables because it will penetrate each end of the cable.  Copper and its alloys react readily in the presence of water and contamination (dirt from flood waters, for example.)  Also, the connector itself may be compromised by corrosion, as will be the solder joints or compression welds performed when the cable was new.  It will only get worse.  Toss the cables.  Just do it.  Life is too short.
  • For pictures of what I do with controls, check my previous post on https://www.unbrokenstring.com/noisy-controls-in-an-swr-red-head-bass-combo/
  • Most guitar pickups are encapsulated with wax or epoxy.  While the pick guard is off, blow out and dry what you can reach.  There may be some very fine wires exposed where they may be damaged, so don’t go crazy with the towel.
  • Reverb tanks have small transformer wound with small wire, like guitar pickups. Also, the springs are fairly delicate. Do what you can to dry them out before rust and oxidation set in. If they need to be replaced, reverb tanks may be purchased on-line for $30-$40 or so.
  • The CAIG Fader Lube is a very good lubricant for tuning machines.  While you’re at it, give them a shot of lube, directing it in such a way that it can enter the tuning machine.  Rinse.  Repeat.

UNDER NO CIRCUMSTANCES USE WD-40 ON YOUR GEAR.

 

WD-40 is good for your wet car ignition, but it has fish oil in it, which is just plain nasty considering that this is the 21st century and you can get modern products for your equipment.  Some people swear by WD-40, and I use it on lawn equipment and tools.  When people use it on electronics and musical instruments, I swear AT them.

Now that you are Poseidon and can command water to go away, here’s another tip.  If your flood water was muddy or contaminated, you can use clean water at anytime on most electronics.  This includes switches, controls, circuit boards, and all the stuff we’ve mentioned so far.  Your electronics were built in a factory that used water to clean the final product.  You can do this, because you know how to remove water.  And you are Poseidon.

FYI, full disclosure – I don’t own stock in CAIG.  However, their products are Top Drawer and are available at Fry’s in the hard-hit Southeast Houston area where I work and live.  In the Northwest part of town, ACE Electronics has the Blue Shower and equivalent lubricants.  These are the products that are available NOW (er… when the power comes back on and the roads are passable..) and are not vaporware.  Just tryin’ to help.

Again, there are several VERY COMPETENT shops in the Houston area that are willing and able to assist with an attempt to recover water damaged gear.  Check the musician groups on Facebook, and do a search for ‘repair’ before you post anything.  Turns out, some guy posts the same question every week or so, looking for a good repair shop.  And the same answers keep coming up again and again.  Don’t be that guy.  I am booked solid out through the end of September and may not be able to take on your work right away.  If you care to contact me directly, I can discuss some options and recommend some Good People who can get you going again.

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Noisy Controls in an SWR Red Head Bass Combo

This combo amp really turns heads whenever it is played.  However, over the decades, the controls have become noisy. Time for the Unbrokenstring Crew to do some remedial magic and get this unit back in top form!

This unit has a 1U rack space under the head unit, which is a nice touch!

 

Let’s take a look around the inside of the unit. The power transformer and heat sink dominate the center of the unit.

 

The preamp is hybrid solid state / hollow state.

 

Looking at the rear of the front panel, we see the input jacks and equalization controls directly mounted and hand-wired to the circuit boards.  Most of the work we need to do today is right here.

 

The configuration switches are seen here.  That big black block in the middle is the top of the heat sink.

 

We see the fan here, which blows the length of the heat sink.  The power transformer has a bit of tape and foam on it.

 

Looking at the inside of the rear panel, we see the power jacks and fuses.  Can you see the bridge rectifier?

 

This big potentiometer dominates the rear panel, setting the line out level.

 

From this angle, we can see a the filter capacitors.  Electrically, this unit is very solid.

 

Each control is rinsed out with some Blue Shower cleaner.  The cleaner is applied from the rear of the potentiometer, rinsing the crud away from the resistive element.

 

Then the control is dried with some compressed air in a can.

 

This anti-corrosive cleaner/lubricant works well on the actual resistive element and wiper.

 

This synthetic lubricant is just the ticket for lubricating the shaft.

 

After reassembly, the unit is checked out.  Note the ease by which the loudspeakers are connected to the head unit.

 

This unit is now fully functional, with no more control noise.  Back together it goes!

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

Ampeg BA115 Bass Combo Amp Repair

Mysteriously, this modern Ampeg bass combo amp quit working.  Could the Unbrokenstring Crew make it right?
The unit appears to be completely dead, with power present at the fuse holder.  Let’s go inside to take a look around.

 

More goodness from St. Louis Music.

 

This picture documents the wiring polarity on the main driver coil.  This needs to be right when reassembling the unit!

 

And the one on the right is the ” + ” terminal.

 

The screws that hold the chassis in the chassis come in from the sides of the enclosure.  The captive nuts in the chassis have sharp corners on them, which snag the Tolex covering that wraps inside the enclosure.  If you ever venture here, beware!  TIP – slip a thin scraper or putty knife between the chassis and the cabinet to keep this from happening.

 

The circuit board is separated from the front panel of the chassis.  Note the white nylon spacers on the jacks to the right and the inside-toothed lockwasher on the rotary encoder to the left.  These come off now and are stored with the knobs lest they fall off and get lost on their own.

 

Do you see what I see?  This white wire carries the AC power neutral to the main circuit board.  The flag terminal came off the main circuit board.

 

The solder used in this unit is ‘lead-free’ and compliant with RoHS, the directive to remove harmful substances from the supply chain.  This kind of solder is brittle, so solder joints made with lead-free solder often fail from cracking stress.

 

This is the other side of the circuit board.  The solder fillets are OK but the mechanical joint failed entirely.

 

Rosin activated flux was added and the old solder removed.

 

Here is another failed joint undergoing rework.  This one is at the DC common point of the amplifier.

While we’re at it, let’s look for other failed joints.  Can you see these?  These are still electrically OK but will fail soon.

 

Let’s put this guy back together.  The shiny metal plate next to the circuit board is the heat sink for the power semiconductors in this unit.

 

These pics were made earlier to document the location of the flying wires attached to the circuit board.

 

These wires carry DC power to an off-board circuit.

 

That shiny metal heat sink gets a new coat of silicone heat sink compound, to minimize thermal resistance to the chassis.

 

Power is applied.  Look, we have an indicator light now!

 

Before final assembly, let’s take one last look around.  See those components stapled to the rear of the cabinet?  That is the crossover network for the tweeter.  Yes, I said stapled.

 

This is the pair of wires that go between the chassis and the crossover network.  When the chassis is installed, this hole will be resealed with RTV to control the moving air behind the main loudspeaker.

 

All back together except for the grille, which you saw.  This unit works very well for a solid state unit.  It is loud, and light-weight.  The future holds many more years of service.for this unit.

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

Kustom KPC15MP Powered Monitor Repair and Refurbishment

This powered monitor/PA box was badly abused but could become the basis for a good keyboard amp.  Could the Unbrokenstring Crew put it back together and make it gig-worthy?

All of the parts are here, but they are rattling around inside.  Electrically, it worked, but the third-world construction techniques rendered the unit worthless for loading in and out of a venue.

 

For instance, the control panel was literally kicked inside the enclosure.  Yes, those are wood brads fired from a nail gun.

 

The trim plate was easily removed.

 

To get a good look inside, the main loudspeaker was removed.

 

There are all kinds of things rattling around inside this unit.

 

The horn driver is shot.  Proceeding with exploratory surgery, the lens is coming out.

 

This driver is threaded, which implies that if it needs to be replaced, a standard compression driver can be selected.

 

This driver is probably a Chinese copy of a Motorola unit.  The series resistor is all this unit has for a crossover network.

 

Disassembling the driver reveals this one-inch cone.

 

Behind the cone is this piezo driver.  It has come loose from its mounting and one of the connecting leads is broken.

 

The piezo element was glued on to the back of the cone.  This is some fine Far East engineering!

 

The resistor in series with the compression driver has miraculously survived the abuse.

 

I am a big fan of these compression drivers.  They are low-cost, covered by a warranty, and compatible with this setup.

 

In this application, it is an equal or better replacement for the plastic driver that we are removing.

 

These crimp-terminals are handy, although we may use some insulated ones that are the same size.

 

This crossover network is compatible with the new compression driver and loudspeaker, plus it is adequately sized for the power levels involved.

 

The only weakness out-of-the-box is that the large inductor needs additional support, particularly if this crossover network is installed in gear that will be loaded out for gigs.  The shiny glue is actually hide glue.

 

Here is the crossover network in its new home.  The main power transformer is on the left and the power amp with the large black heat sink is on the right.

 

Shifting out attention to the user interface, the control panel is separated from the piece of MDF board.

 

A quick inspection of the power amp reveals that it is functional.  However, temperature cycling and vibration have broken a couple of solder joints.  These will be repaired before returning the circuit board to service.

 

I tried to drive the brads out of the MDF the same direction that they were driven in.  However, they were VERY firmly stuck in the wood.

 

I decided to just trim them flush and get on with the process.

 

This black marker is adequate to disguise any exposed MDF around the control panel.

 

This piece of MDF will be glued and screwed in place from the inside of the cabinet.  Here we are pre-drilling the MDF to prevent the screws from splitting the thin material.

 

These screws will be driven from inside the cabinet.

 

Oh, look here!  More stuff rattling around inside the cabinet!

 

I wonder where this goes?

 

The control panel is about ready to reinstall.

 

A little glue is spread around the inside of the main cabinet where the control panel will be fastened.

 

The control panel goes here.

 

A socket wrench drives the bit, seating the screws.  Not much room here for a powered driver.

 

This is another view of the control panel mounting scheme and the 100 watt amplifier.

 

The AC power for the amplifier is filtered by the yellow across-the-line capacitor seen on its own circuit board.

 

Time to start putting things together for real.

 

We’re drilling a hole to mount an L-pad attenuator that allows the user to set the level of high frequency audio coming out of the horn.  The fixed resistor seen above will be eliminated by this L-pad.

 

The L-pad level control looks almost factory.

 

The main loudspeaker seems OK.

 

Some closed-cell foam is installed around the loudspeaker to seal the cabinet.  Peeling the white paper backing reveals  an adhesive back that keeps the foam in place.

 

More foam is used to seal the space around the horn lens.

 

I might drop something down inside the horn lens while working with this unit, so I stuffed a rag in the lens to catch whatever I might drop.

 

The edge of the horn driver magnet just touches the back of the control panel circuit board.  Oops.

 

A durable insulator was fabricated from a bit of junk mail.

 

Now, this thing is LOUD!  We shall declare this bit of reconstructive surgery a success!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Fender Rhodes Electric Piano Amp Refurbishment

A Southeast Texas area church had a wonderful Rhodes Piano that needed some attention.  Whenever the unit was powered on, a loud hum was all that came through the speakers.  Time for the UnbrokenString Crew to go to work!

The Fender Rhodes Piano consists of a keyboard section, containing keys, action, and tuned rods that work in the same manner as tuning forks. The rods vibrate when struck, and the motion is sensed by a coil not unlike a guitar pickup. From there, the signal is sent to the other section, a powered stereo loudspeaker assembly seen here.

 

The speaker cabinet is two-faced e.g. loudspeakers fire from both the player’s side and the audience’s side.  A pair of loudspeakers are assigned to each output of a stereo amplifier.  The pairs of loudspeakers are across from each other in the cabinet, one firing forward and the other one back.  This enhances the swirly, phased sound of the instrument.

 

These loudspeakers are Fender branded CTS units.  The metal box in the background contains power and input circuitry.

 

CTS built these loudspeakers in June of 1975.

 

This part number indicates that these are 32 ohm AlNiCo loudspeakers.  This is a standard-issue Rhodes Piano unit.

 

This voice coil is totally cooked.  The motor drags badly in the magnet.

 

This voice coil is open-circuit but moves smoothly in the magnet.  Is a repair possible?

 

There is the broken voice coil wire.  This wire is really cooked, so we will elect to replace the loudspeaker with a pair of modern 8 ohm units wired in series, to yield the proper 16 ohm load to the amplifier.

 

We have removed the panel at the end of the cabinet.  The power transformer is visible to the right.  Each channel has a separate input here.  Also, a special cable from the Rhodes keyboard attaches here.

 

The power cord for this unit is no different than an extension cord.

 

Instead of a regular extension cord, we will use a SmartPower unit to power-up the unit and protect it from surges.  Think ‘mini-Furman unit.’  I also sell these, BTW.

 

These transistors read as short circuit.  I think we now know everything we need to know to make an intelligent quotation.

 

Name, rank, and serial number please.

 

One output of the power supply assembly is 25vdc for the keyboard section.

 

The keyboard voltage is set by a potentiometer accessible through this hole.

 

The power supply filter cap is in great shape for its age!

 

Likewise, these guys look great and test good.

 

Everything here is as it should be.

 

Steven removed one of the damaged loudspeakers.

 

Over the years, the gasket glued itself to the cabinet.

 

A little extra cleanup won’t hurt a thing.

 

The circuit board for the power amplifier is a hand-drawn affair, typical for the 1970s.

 

The board designer was nice enough to add is some text that would help the amp tech find his/her way around.

 

Some power resistors were burned up.  All of the components to the right of the transformer were replaced.  The transformer is for inter-stage coupling, not power.

 

Some power transistors were hand-selected for duty in this amplifier.

 

The repaired amplifiers are re-installed in the bottom of the cabinet.

 

We are ready for final test!

 

Amplifier design has certainly changed over the years.  This is a unique design that has withstood the test of time very well!  The customer was VERY pleased with the finished job.  Weather Report Cover Band, anyone?

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Peavey Citation MK IV Two Channel Guitar Amp Head Repair

Rod had this Peavey head kicking around and thought it was time to put it to good use. However, it didn’t work at all. Could the Unbrokenstring Crew work its magic and bring this road warrior back to life?
A quick scan of the front panel shows that the input circuit sports the sort of flexibility that the Peavey Marketing Department loves to explain to anyone who would listen…
Each channel has independent gain, and a master volume to Rule Them All.  Effects can be inserted via the front panel.
On the rear panel, we have parallel speaker jacks and the usual ground/no-ground power switching.  Peavey often married different front panels, which contained preamp circuitry, to different rear panels, which carried power and audio amplifier components.  The ‘series’ number goes with the power amp, not the front panel.  We Got This.
Name, rank, and serial number, please.
Pulling the front panel, we see that all of the components are mounted on one circuit board.
I took a few pictures to be sure that the wiring and cables were returned to the same spot when we are through.
The cable to the right is just wired to the power indicator.  The other two carry signals.
This is a better view (to be sure that they cables are properly oriented on their pins.
The front panel is free of the rest of the unit.
All of the controls and switches will be cleaned so this assembly comes completely apart.
We can now clean and lubricate everything now.

 

Can you spot the broken solder joints?
Someone has been here before!  This needs to be cleaned up, too.
The Blue Shower is a good cleaner.  The DeoxIt contains a lubricant for the potentiometers.  Good Stuff!
Back Together it all goes!
This screw hole was stripped out.  First, we will soak the stripped hole in the wood with this wood hardener.
Next, a birch dowel is cut to partially fill the hole.  The dowel reduces the apparent diameter, allowing the screw to hold.
With the stripped hole repaired, we are back in business!
This unit plays very well, and all the controls and switches are Like New!

 

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Blackstar HT5RH Guitar Head is Dead

This five watt head had gone nearly silent. The national retail chain that sold it told the owner to purchase a new one, because that’s their business model. Could the Unbrokenstring Crew repair this unit and bring it back to life?

At five watts, this head is bedroom-friendly, yet there are plenty of opportunities for distortion and tone shaping.

 

Interestingly, there are three options for outboard speaker cabinets as well as all of the usual in’s and out’s.

 

The back comes off with these screws.  But it appears to be stuck in place!

 

I speculate that when the unit was built, the Tolex glue was still fluid and squeezed out between the back and the frame, sticking the rear cover in place.

 

The chassis is held in with these screws.  No surprises here.

 

This is a hybrid solid state / tube unit, with a 12AX7 triode pair in the preamp section and a dual triode 12BH7 pressed into service as a push-pull tube output stage.

 

There are two different versions of the schematic available.  They can be easily identified by checking the number of conductors in that big ribbon cable that connects the rear panel circuit board to the main circuit board.  This particular unit uses the cable with 21 conductors.  Thanks to Armando Garcia at Mars Electronics who furnished this schematic!

 

In the foreground are the big heat sinks for the voltage regulators.  The rear panel wiring board is in the background.

 

Viewed from the other side, the main circuit board contains the preamp circuitry.

 

The preamp uses DSP techniques to create the reverb effect and the tone-shaping functions of this unit.

 

This is the preamp tube.  It’s fine.

 

This is the 5 watt output tube.

 

This part checked OK but it is a little weak.  We will continue to use this unit for troubleshooting purposes.

 

This is the pin-straightener from my tube tester.  The Chinese tubes have a little larger envelope than the JAN versions of these tubes, so the tube is a tight fit in the straightener.  If the tube envelope is too large, the pins can be straightened using the same tool, but the pins are inserted from the other side of the straightener.

 

So the output drive signal is split into an in-phase and out-of-phase copy, and applied to the grid of the output tube.  But the plates of the 12BH7 are stuck at +300 volts.

 

The primary windings of this output transformer are shorted to each other.

 

Let’s get this transformer off the chassis and take a closer look at it.

 

These Chinese transformers are usually not worth fixing, but this transformer is hard to find.  Some exploratory surgery shows us that the problem is deeper in the windings and not readily repairable.

 

So, out it comes entirely.  The search is on for a replacement.  The original manufacturer has no stock.

 

Hammond makes a versatile aftermarket unit that is available through distribution.  We can make this work!

 

The frame of the transformer is just a little bit larger than the original part.  One of the mounting holes is being moved.

 

Placing the magnet near the site where the drill is working helps keep those pesky metal shavings under control.

 

The new transformer is bolted in place and some Thread Locker is applied to the bolts to keep it in place.

Here the output leads are threaded through the insulating grommet in the chassis.

 

The input wiring is soldered into place, so the leads are trimmed to length.

 

To preserve the original wire insulation colors silkscreened on the circuit board, short pieces of the original wiring were left in place and butt-spliced to the new output transformer harness.

 

This unit is ready to test.  Pretty neat looking!

 

Surprisingly, this unit has a bias pot and a balance pot.  However, there is no commonly-available information available for the technician to set these.  So, I wrote this procedure:

BALANCE ADJUSTMENT

  1. Set DMM to mV range
  2. Affix DMM probes to TP6 and TP7
  3. Switch POWER ON; switch STANDBY ON after five minute warmup.
  4. Adjust BALANCE pot for 0V display on DVM
  5. Switch all power OFF

BIAS ADJUSTMENT

  1. Affix black DMM lead to ZD2 cathode (banded end) near Input Jack. This is a convenient GND.
  2. Affix red DMM lead to D20 anode (not banded end.)
  3. Switch POWER ON; switch STANDBY ON after five minute warmup.
  4. Adjust BIAS pot so that DMM display is 46mV.  This puts about 10mA of idle current through the 12BH7.

Recheck BALANCE and BIAS adjustments as they are slightly interactive, particularly if the internal sections of the 12BH7 tube are not matched.  Follow all the usual precautions of removing power and working safely around high voltage!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626