Wonderfully-preserved from the era when one could still see Stevie Ray Vaughn perform live, we find a Boss Chorus Ensemble pedal that had been stored for decades. In the years since, many advances in computer sound modeling has made an infinite universe of tone available to the aspiring guitarist. However, there is just ‘something’ about the Real Thing. The owner wanted this wonderful piece of history refurbished and placed back into service.
Years of storage in the high Houston humidity has taken a toll on the outside. What’s up with those screws on the HIGH/LOW input level switch?
Forget that stuff made in China. This is the real thing, from Japan!
Since when was an electric guitar considered “HOUSEHOLD ELECTRONIC EQUIPMENT”?
The nomenclature for the input and output jacks appears on the top of the unit.
Let’s make a quick tour of the unit. This is the left half of the front panel.
This is the right half of the front panel.
Several pictures of the circuit boards were made, to verify that the service literature used for this refurb matched reality. This is the top half of the circuit board’s component side.
This is the bottom half of the component side of the circuit board. Those fuses are on the AC output of the power transformer.
Most of the screws in the bottom of the unit were missing. This unit was balancing on two feet.
The interior layout is actually pretty cool, well-representing the line-powered Japanese gear of the period.
I’m going back through and documenting where the various wire colors go. Note that the wires are just tacked to brass eyelets swaged into the circuit board. The AC power wires get their own riveted tie points.
Looking closely at the wiring.
Wiring closeups.
More wiring closeups. This is factory wiring, I believe.
More colored wires.
The black ground wire gets its own lug.
A quick jab of the soldering iron frees the circuit board from the wiring harness. All passive components were checked and anything that was out of spec was replaced. Most of the forty-year-old electrolytic capacitors were replaced.
The outer jacket of the AC cord dry-rotted. This looks gnarly, but the inner insulation seems to be fine.
A new cord is identified with the same outer diameter and wire gauge.
The blue and green wires are the input to the primary wiring of the power transformer. Note the cable clamp pressed into service as a strain relief for the power cord.
The old cord is gone. We can keep the cable clamp and move it to the new cord set.
This grommet would not ‘fly’ with UL today, but was fine for the 1980s. This will be used again.
The new cord is stripped back. Note the authentic cotton filler.
The cotton mop is trimmed away and the original cable tie is slipped on the new cord. Next comes the grommet.
The original strain relief was retained. The white and black wires were later terminated to the green and blue wires seen above.
Both foot switches were ruined. Out they come!
This is the wiring side of the original ‘effect/bypass’ switch.
Out it comes. The escutcheon is in rough shape. Maybe we can freshen it up.
Here we’re trying to salvage some of the original hardware. A sideways blow the old foot switch damaged the threads.
Here is the wiring side of the chorus/vibrato switch. This switch was intermittent.
Rather than desolder the wires, I trimmed them off square. They will be stripped and re-terminated on the new switch.
A pair of DPDT foot switches will adequately replace the foot switches in this unit.
The original trim nuts were in good shape and will be reused, to preserve the original appearance of the unit.
Now let’s move our attention to the potentiometers and switches in this unit.
The nuts were rusty but in good shape otherwise. Here, one of my deep sockets with the felt cover is used to remove the nuts. The felt prevents the socket from marring the soft aluminum face plate.
Note the letter “C” after the first line of text. This denotes a reverse taper pot, used for the vibrato rate control.
Vibrato depth control is a linear taper control, thus the letter “B.”
The chorus intensity control is a linear control as well.
And who would have guessed that the level control was an audio taper potentiometer?
Each potentiomenter was flushed with Blue Shower.
A blast of Rid-Ox really does the trick on dirty contacts.
Some synthetic lubricant keeps the shaft turning smoothly.
Until I get the air compressor line plumbed to the bench, Air In A Can will have to do to dry everything out.
This process leaves everything spotless and clean, inside and out!
A soft tooth brush works well with the crinkle finish paint used on this unit.
The toothbrush cleans the grooves around the indicator lamps.
A lint-free cloth carries away four decades of gunk.
Before going further on the outside, we need to get under the front panel.
With the potentiometers and switches removed, the aluminum panel lifts right out.
Placing the aluminum panel flat on a carpeted surface, gentle pressure will allow us to remove dents.
With the front panel set aside, we can turn our attention to the power switch. This switch needs cleaning as well.
It gets a treatment similar to the one given the potentiometers. This is much better!
With the individual pieces reconditioned, it’s time for reassembly.
Controls and switches were installed and wired. The wiring harness was returned to its factory layout.
We’re starting the process of restoring all the connections made by the colored wires.
Testing was performed with a sheet of cardboard between the circuit board and the metal chassis.
I spotted these parts at a local hardware store. These screws and bumpers are perfect for replacing the rubber feet.
This guy is ready for another four decades of vintage guitar sound. This unit sounds AMAZING!
Thanks for reading all the way through!
CONTACT – David Latchaw EE
281-636-8626
This microphone is a basic SM58 capsule coupled to a battery-operated VHF FM transmitter.
These are often seen in many performance venues as well as in worship, news-gathering, and business settings.
The 9v battery has leaked. We will need to disassemble the unit to clean up the mess.
These VHF units are on frequency allocations that are shared with other services and may be subject to interference. However, these units work well if you are fortunate enough to be in a part of the country where interference is low.
The microphone capsule is built into the head of the microphone, which unscrews from the electronics. Connections between the capsule and the electronics are reliable regardless of how many turns are necessary to tighten the threaded bodies together.
The gold fingers touch those rings seen in the previous picture.
This inside snap ring keeps the electronics inside the housing.
Before we remove the electronics,we need to get the switch actuators out of the case. The cover removes easily enough.
The switch actuators come straight out.
This is looking good!
This is the complete analog FM transmitter.
Working with the battery contacts is much easier now that the case is out of the way.
Reassembly is the reverse of disassembly. Wow, that’s profound…
These big tweezers are all I need to get the inside snap ring back in place.
Reassembled, the new battery is installed and we have a green light!
The receiver indicates that an FM carrier is present.
We have an intermittent problem with audio out of the microphone. We need to look at the capsule.
I guess we’ve screwed the pooch by now.
The wires are cracked where they emerge from the solder joints. These will be reworked.
This brass adapter goes between the capsule and the rest of the housing.
We are back together again!
