CA Guitar Repair Blog: Harley Benton MB-20BK Electric Guitar Gets Some Help

Preamble

This Harley Benton MB-20BK Electric Guitar was at CA Guitar Repair in 2024 for servicing, restringing and a setup; and left the shop with all stock appointments retained. Fast forward to last month, and owner Amirul's here once again with his main squeeze. This time around, he's requested a pickup swap and shielding, besides servicing and restringing. No hay problema, mi amigo! Now, let's take a look at what's been done so far.

Electronics Evaluation and Upgrades

The first thing I did after detaching the neck from the body was to disassemble body-mounted hardware and electronics for evaluation and servicing. Following this, I checked the bridge ground for continuity, and discovered to my delight that it was working as it should.

Hardware and Electronics Disassembled

Bridge Ground Checks Out OK

Next, the stock 500K mini pots were evaluated. As they were caked in salt and grime, they would not be retained. The stock open frame toggle switch, meanwhile, was tarnished and showed signs of corrosion. As such, it too would be replaced. Subsequently, electronics upgrades agreed upon included a shielded output jack cable, full-sized Alpha A500K pots, an Epiphone toggle switch, a K73-16 0.022uF tone cap; and Switchcraft output jack socket.

Mini Pots Encrusted in Salt

Tarnished Toggle Switch

Upgraded Components

Test-fitting the replacement Alpha pots proved to be frustrating, as the existing pot mounting holes were way too small to accommodate full-sized pots. And so, these holes were carefully enlarged with a tapered reamer, after which the Alpha pots slid into place rather easily.

Alpha A500K Pot Will Not Fit

Reaming the Pot Mounting Hole

Alpha A500K Pot Now Fits Nicely

Evaluating the Replacement Humbuckers

The used Epiphone humbuckers, a gift from Amirul's dad, needed to be checked thoroughly before being installed. Thankfully, both were working. DCR readings were 9.07K for the neck, and 9.66K for the bridge.

Pickup Upgrade - Epiphone Humbuckers

Neck Humbucker DCR is 9.07K

Bridge Humbucker DCR is 9.66K

Matters of Shielding

As Amirul had specifically requested that shielding be installed in his MB-20BK, we first had to clean the pickup and control cavities. Here, a small wire "toothbrush" and razor blade came in very handy for removing most of the dried polish residue and embedded dust particles.

Cleaning the Pickup Cavities

Cleaning the Control Cavity

With the cavities adequately prepped, the first coat of conductive graphite paint was applied with an artist's brush. A total of six coats were laid down nice and thick, with about an hour's drying time in between coats.

Applying Shielding Paint - Pickup Cavities

Applying Shielding Paint - Control Cavity

Once the final coat had dried completely, I was able to test shielding continuity with an ohmmeter set to x1K ohms. Thankfully, the readings obtained were invariably 0 ohms, indicating that the shielding paint would do its job. Oh, I almost forgot the control cavity cover shielding. Now, although the cover came with stick-on metal foil shielding, continuity was inconsistent. This being unacceptable, an additional layer of copper foil shielding was applied, and this worked like it was supposed to.

Testing Pickup Cavity Shielding

Testing Control Cavity Shielding

Testing Control Cavity Cover Shielding

Cleaning the Fretboard and Frets

I remember thoroughly cleaning and oiling the amaranth fretboard on this MB-20BK the last time it was here, as well as polishing all 24 jumbo frets. Well, looking at the first pic below, it's as if none of that ever happened. No worries, though. We'll clean things up with abrasive pads, sandpaper on a popsicle stick, naphtha, and lots of elbow grease.