December, 2018 - Unbroken String

Boss DD-20 GigaDelay Pedal Needs Direction

December 30, 2018 by latchaw

Every function on this pedal works properly. Except, the user cannot select menu functions without a lot of hassle. And, the delay time can only be increased, not decreased. Can the Unbrokenstring Crew decode the mystery and make this unit a little less of a pain in the rear to use again?

The unit turns on and works, but the delay time knob only increments. This makes it almost impossible to select any function or mode unless the user spins the knob all the way around to wrap back to the beginning of the menu. And there is, like, three hundred menu items.

Everything is accessible from the bottom. The vertical strips are Velcro hook material, to hold the pedal in place on the pedal board.

The black plastic rectangle on the left is a battery box. On the right is a stack of circuit boards.

Removing the circuit boards involves removing the nuts on these jacks.

The ribbon cables interconnect the two main circuit boards.

The metal piece around the jacks is really part of the noise shielding of the box.

We can tip out the bottom board now that the jacks and power adapter jack is free from the rear panel.

Interestingly, this little crescent moon-shaped piece is a bushing that makes a small hole out of a large one. This may have been a design feature for another model of pedal, or, more likely, the result of an engineering change. Or, my favorite theory, a design screw-up.

Back in the early days of electronics, stiffened cardboard was coated with wax to make insulating sheets called ‘fish paper.’ Nowadays, we have synthetic equivalents. This insulating sheet separates the two circuit boards.

To gain access to the top circuit board, we need to remove the control nuts on the top side. This is the knob for the delay select function. The knob works fine, the function it performs does not.

This plastic bushing covers a larger hole and allows the knob to be recessed below the plane of the top panel.

These other controls are more conventional in their mounting scheme. Those hex drive screws are for looks, and only hold the bezel down on the top of the pedal enclosure. We don’t have to mess with them today.

At long last, we are able to remove the upper circuit board.

We already have a pretty good idea that the rotary encoder for the delay function is not working properly. To verify that, the unit is partially reassembled for electrical test. The cardboard is more insulating material to keep everything from shorting out. Kinda like home-made fish paper.

The unit is running and the oscilloscope can tell us if the two phases of signal are coming from the rotary encoder. The answer is, one phase is missing. Thus, the rotary encoder can only appear to electrically ‘spin’ in one direction.

So, it’s time for the old rotary encoder to come off the circuit board. A soldering iron will melt the solder and this Solda-Pullit will remove the molten solder.

The new rotary encoder is installed, as shown. This rotary encoder also has a built-in momentary switch that is actuated when the shaft is pushed down towards the circuit board. Or, in use, when your foot taps the knob while playing.

Pretty nice workmanship, wouldn’t you say?

Re-assembly is the reverse of dis-assembly. There are a lot of parts here, so this unit will go back together with the help of all the pictures we took earlier.

The insulative sheet goes here.

The bottom assembly goes here, with the requisite white cables. Don’t forget to re-install the little crescent-moon-shaped piece where the connectors poke through the back panel. I did, the first time. Oh, yeah, and the metal shield, too.

Many of the Boss pedals use this barrel connector for power. The shell of the pedal housing slide into the slots molded in the connector to firmly hold the power connector in place. Note that not all barrel connectors have these slots. If you ever replace a Boss pedal power connector, verify that the replacement part has the slots.

This is a little better shot that shows the proper orientation of the shield plate. The little sharp fingers around the outside edge should point away from the middle of the pedal, so that they can ‘bite’ into the pedal housing.

The red and black cable carries power from the internal battery box that we saw in the picture above.

The unit is cleaned up and all the knobs reinstalled. Ready for test!

All functions work flawlessly, PLUS the rotary delay time knob both increases and decreases delay time and allows the user to scroll up and down through the menus. I think we’re done here!

Thanks for reading all the way to the end!

CONTACT – David Latchaw EE
281-636-8626

Carvin MTS3200 Amp Head is the Victim of Hurricane Harvey

December 23, 2018 by latchaw

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

December 23, 2018December 16, 2018 by latchaw

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

December 23, 2018December 9, 2018 by latchaw

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

December 23, 2018December 2, 2018 by latchaw

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.