PreSonus StudioLive 18.0.2 Mixer Is Resurrected from the Dead

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Richard relied on this unit for much of his sound, and when it went dark, he had to get it fixed or change his entire setup. Could the Unbrokenstring Crew bring it back to life and preserve Richard’s workflow?

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Our Cajun neighbors designed and engineered the mixer.

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Two screws hold on the side trim pieces.

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Once the screws are removed, the whole trim piece slides to one side and all these machined studs come out of the slotted holes. Nice.

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These side panels provide most of the mechanical strength of the finished assembly. Lots of little black screws hold them on. The red plastic tray on the right keeps them off the floor.

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Inside the panels, we see tell-tale signs that the Magic Smoke has been released. Please understand that Magic Smoke is a very, very technical term.

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Whenever the Magic Smoke is seen escaping from electronic components, they stop working. Therefore, all electronics must operate based on the principle of Magic Smoke. And you thought it was voltage and current…

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The fasteners used throughout the unit are tiny Torx machine screws.

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Sooner or later, all those knobs will need to be removed. For now, we will just remove the top row of knobs.

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Now we can separate the rear of the unit from the front and back.

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Power and data go thru these cables. I snapped a pic to be sure that they are oriented correctly when the unit is reassembled.

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The brick red connector is a push-on terminal that connects the chassis grounds together. It must come off, but it’s in a recessed spot between circuit boards.

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But the chopsticks came in handy and the ground terminal is free.

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More pics to document where the cables go.

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This is where the AC power is applied to the power supply assembly.

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The safety ground is the green and yellow wire. AC hot and neutral are applied via the mesh-covered cable on the right. A fuse, surge suppressors, and a temperature-dependent resistor are seen here, along with AC-line-rated filter capacitors and a filter choke. BTW the fuse is fine.

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AC power is rectified and stored in the large capacitor in the foreground. The rectifier array is seen between the yellow blocks in the lower right hand side of the circuit board.

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After years of service, the capacitors are swelling. Look at the top-facing end of the black cans seen in this picture.

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When electrolytic capacitors swell, the chemicals inside are reaching end-of-life. The capacitor begins to dissipate more heat and energy storage in the capacitor itself become less efficient. And this cap is next to a heat sink, which likely is warmer than the surrounding areas on a good day.

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More swelling. These eventually pop and make a huge mess.

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Looking at the reflection on the top of this device, we see signs that Magic Smoke escaped from this part.

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This part is a power field effect transistor (FET) and will be changed out. Electrically, each pin is shorted to the other.

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Magic Smoke has escaped from the end of this diode.

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More magic smoke was seen in the vicinity of this part. These are cheap enough that it will be replaced.

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Here is the new power FET, ready to be bolted in place. Only after the FET is fastened in place will it be soldered to the circuit board, assuring us that the solder joints will not be under mechanical stress.

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I tried to match components, but this big red gaudy storage capacitor was the only color available. Esthetics Fail. Sorry.

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Every electrolytic capacitor in the power supply was changed. The suspected bad semiconductors have been replaced as well.

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Fortunately, whoever did the circuit board design silkscreened the voltage values next to the pins where these voltages can be measured.

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Armed with that information, we can test the power supply and verify that it is functional before connecting anything else that may be damaged if the power supply is not functional.

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We are ON THE AIR! Everything works as it should. Except…

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Can you see the cloudy area on the left edge of the LCD? That is not a reflection. That is more Magic Smoke. The LCD is fully functional, but this is just plain unacceptable.

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To gain access to the LCD, we need to disassemble the keyboard portion of the unit. And remove the rest of the knobs.

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With more screws removed, we have access to the LCD assembly.

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Opening the LCD allows for the inside of the lens to be cleaned and polished, removing the Magic Smoke.

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While the keyboard is apart, the sheet metal panel can receive a little TLC.

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Aw, what the heck. While we’re here, let’s inspect the remaining circuit boards, looking for aging capacitors and signs of Magic Smoke.

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An effects processor IC is seen here, along with many hybrid analog gain blocks. No schematic would help us through this maze. But everything here is in Tip Top Shape.

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Reassembling the panels together is best done with the unit on its side.

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Having the unit on its side allows access to all the internal cabling that needs to be reconnected. Glad that we had all the pictures!

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Some of the small cables need to be reconnected at the last step as they are barely long enough to reach their destination.

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Oh, and here’s that chassis ground terminal. We got it apart somehow…

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So here we see it almost mated. This step was completed with some very long needle nosed pliers.

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With the LCD cleaned, this unit appears ready to test again.

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All functions work. All lights light up. Life Is Good!

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Fender MIM P-Bass Gets Upgraded Pickups

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A famous Houston Jazz Cat sought out the services of The Unbrokenstring Crew after hearing about us by word of mouth. This instrument was at home on the stage and in the studio, but just needed a little something more. Could The Unbrokenstring Crew supply that ‘little something more’ and get it done before this Friday’s gig?

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This instrument was a dead-stock, straight-ahead jazz bass, just a little funk added in for fun.

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We will reuse the strings, so they are just pushed back through the bridge to get them out of the way. The original bridge pickup is already loose from the body.

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A peek under the cover shows the smooth, unscrambled, automated winding used on these factory pickups.

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To access the neck pickup and get to the wiring more easily, the pick guard is removed.

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Black and white wires go to the neck pickup. So far, so good.

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And, black and white wires go to the bridge pickup. We need to keep all these wires straight. Or gently curved, as the case may be.

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The burned insulation and cold solder joint on the tone pot tells me that the factory wiring was done in a hurry. The Unbrokenstring Crew is in a hurry, but not this much of a hurry.

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The original neck pickup ohms out at 5.14k ohms.

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The original bridge pickup is not that different, measuring 5.51k ohms. The original pickups were labelled and returned to the owner.

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Our Jazz Cat chose these pickups for his instrument.

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Rio Grande pickups are built here in Houston, Texas. FYI, for the last five years, customers of The Unbrokenstring have asked to have Rio Grande pickups installed in their instruments more than any other brand.

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The Unbrokenstring Crew is curious about how these new pickups measure up. On the screen of the Fluke meter is the resistance reading of the new neck pickup. A lot of wire is used to make this pickup!

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This is the resistance of the new bridge pickup.

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Wiring for the bridge pickup is snaked through the bore in the body, along with the cavity ground wire. The pick guard does not cover this part of the instrument, so cavity wiring needs to be tunneled through the body.

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The bridge pickup settles into its new home.

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Wiring the neck pickup is a little easier as the control route extends to the neck pickup cavity route. With the wiring done and everything temporarily in place, a quick sonic check is performed with my Massive Marshall Full Stack.

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The J-Bass is reassembled and ready for re-stringing.

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If you look closely, the brand name on the pickup covers can be seen. Pickup height is approximately same value as was used to install the original pickups, but our Jazz Cat already has his #1 Phillips screw driver ready and will set the ‘just right’ height by ear.

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Fender Vibro Champ Combo Amp ‘Almost’ Lost to Hurricane Harvey

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Texas Amplification, operated by the late Darryl Shifflett, built some of the finest Fender Blackface clones available. Much of the inventory of Texas Amplification was subjected to the flood waters of Hurricane Harvey. This newly-completed combo amp was high enough to escape immersion, but did not escape the subsequent rain, humidity and condensation. Could the Unbrokenstring Crew make this new unit like-new again for its new owner?

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The nickel plated feet and corner hardware are new, but a light coating of rust from the screws has leached onto the hardware. The Tolex covering appears to be unaffected by the water.

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Here’s a close-up of the rust. Not a big deal, but this triggers my OCDC (like obsessive-compulsive disease with a bit of AC/DC tossed into the mix.)

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The back panels of the amp are held on with the Correct screws, but they are showing signs of iron rust as well.

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This back panel is plywood. It had been wet but had been slowly drying out and was no longer warped. Surprisingly, the Tolex covering was still glued in place.

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This bit of Tolex covering, however, had become unglued.

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The Jensen loudspeaker was high and dry, but we’ll check it for any damage.

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The loudspeaker is more-easily inspected by removing the baffle board.

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With the baffle board out, it’s easy to verify that everything is in good shape.

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More importantly, no apparent water damage had occurred here! The Unbrokenstring Crew is fairly certain that this amplifier was at least partially submerged at the height of the flooding. This loudspeaker and grille cloth appear unaffected!

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Rust Biox is a tool of the museum curator. When old objects are carefully cleaned and restored for display in a museum, such as old weapons or other artifacts, Rust Biox slowly removes iron rust while preserving the un-oxidized material under the rust. This was once sold in the United States as an automotive rust remover, but did not become a ‘hit’ and was removed from the market. The Unbrokenstring Crew, however, is just cool enough to have a source.

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After each item is processed with Rust Biox, a water rinse and hot air dry prepares it for re-use.

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The feet of the unit are nickel-plated steel over a rubber bushing. Here, the bushing is separated from the metal foot for processing.

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These screws hold the feet onto the bottom of the amplifier cabinet.

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The metal feet are restored. Next, the Rust Biox will remove the rust stains from the rubber feet.

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Interestingly, this line may have been the ‘high water mark’ and so this unit could have been partially submerged. Furniture polish will clean and condition the Tolex covering to like-new condition.

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Heat from the hot air pencil softens the Tolex adhesive. The hot Tolex is pressed into place and allowed to cool.

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The hot air pencil has done the trick! This cabinet appears to have never been wet.

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The electronics are brand new, with no signs of water damage or corrosion.

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The Fender Vibro Champ is a single-ended Class A design, a low-parts-count, simple-to-build amplifier with surprising response and tone.

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All magnetics used in Texas Amplification products are procured through Mercury Magnetics. Top-of-the-line!

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The violet jewel in the pilot light tells us that we are ready for business!

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All back together, this amp is running a four-hour-long burn-in to verify that it is 100%. …And dry out anything still wet. This unit was delivered to its new owner, who promptly placed it in his recording studio.

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Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Squire Jagmaster Gets a Total Make-over And Then Some! Part Four of Four

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In Part Three of this project, The Unbrokenstring Crew installed a unique cut-out switch in the pick guard of this guitar. One more thing… Now that the instrument is play-able, the original plastic Squire nut is cracked. Grrrr…

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The old Squire nut came out in pieces.

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Let’s make a new one from Vietnamese water buffalo bone. The blank we’ll use today is shown above the old Squire plastic nut.

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Not to brag or anything, but these bone nuts are truly a renewable resource that I am privileged to legally import from overseas. CITES can go bite it.

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The eighth inch chisel easily cleans whatever glue Squire used to install the original plastic nut.

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This slot is ready for the new nut.

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Sorry, that’s as clean as I can get it.

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The new blank nut is thickness-sanded to fit the slot. I’m doing this by hand because the blank is very close to the proper dimensions to begin with.

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The inside radius is established by using the actual neck as a radius block.

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The side contour is also established by hand, on the actual instrument.

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The actual height of the fret wires is measured in order to calculate the depth of the string slots. This dial indicator measures the installed height of the fret wire above the finger board.

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Here, we’re gluing the new nut right to the finger board using hide glue. A water-based adhesive could cause the wood to swell; shrinkage over the next few months as the wood dries out would throw off the accuracy of the nut slot depth. Can’t have that!

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The old nut is used as a template to establish string spacing. A couple of old strings are used to align everything.

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Now that we know the fret height, string gauge, and string spacing, we can begin establishing the string slots. At the nut, the string slot depth is constant across the radius of the finger board, regardless of the string diameter.

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With a set of old strings in place, the top of the nut can be quickly contoured so that the top of the nut will not protrude above the strings. The geometry of the top of the nut is established in part by the diameter of the strings, which is, of course, not constant across the radius of the finger board. This three-cornered triangular file belonged to my father.

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This old triangular file is just the thing to contour the nut further, smoothing out sharp corners and preparing the nut for polishing.

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Note that the string centers are just below the top of the nut, and that the top of the nut is no higher than any string.

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This is the instrument, as delivered. The Vietnamese water buffalo bone is a spectacular material for musical instruments: incredibly hard, uniform throughout its bulk, and capable of a fine polish without additional waxes or oils, making a visually attractive nut and providing a stable, polished string slot that allows for smooth and stable tuning without binding or sticking. What more could you ask?

I think we’re finally done with the Jagmaster Make-Over!

Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626

Squire Jagmaster Gets a Total Make-over And Then Some! Part Three of Four

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In part two of this series, The Unbrokenstring Crew converted this instrument to a Tune-O-Matic bridge with a Bigsby tremolo. Now The Unbrokenstring Crew will add a cut-out switch to this instrument.

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Matt has specified this exact spot where he wants the cut-out switch installed. The sharp point of an Exacto knife marks the exact center of the hole where the new switch will reside. Because that’s why they call it an Exacto knife.

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We need to remove the pick guard, so off come the strings. Again.

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This nylon washer is used in the Bigsby system to, among other things, set the working height of the lever. Keep track of this!

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A pilot hole is bored where the Exacto knife made the mark seen earlier.

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The copper foil around the new switch hole is cleaned. We are now ready to install the new switch.

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The resistor is installed across the contacts to limit the audible ‘pop’ that you sometimes hear when switching low-level circuits, like the circuits found in guitars.

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Step Three is complete. This switch is not a push button, but is a spring-loaded momentary, center-off switch. Matt can quickly flick it from side to side for a very cool effect.

But wait! There’s more! In the last installment of this project, the cheap Chinese plastic nut has cracked. Tune in to see how The Unbrokenstring Crew upgrades the nut. Like A Boss.

Thanks for reading all the way to the bottom!

CONTACT – David Latchaw EE
281-636-8626