Ibanez / Stratus TS-9 Clone Pedal Repair

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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

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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

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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

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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

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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