CA Guitar Repair Blog: Yamaha AES620

Part One | Part Two | Part Three

It had been a while since I'd last seen this Yamaha AES620. Seven years, in fact. In all this time, quite a few things had changed. For one, owner Izzat had installed a trio of rather ill-fitting set screw dome knobs. They'd have to go, of course. He'd also pointed out, amongst other things, that the electronics were beginning to malfunction and needed to be upgraded.

Components to Be Upgraded

I was also informed that the original bridge-position Seymour Duncan JB had died somewhere along the way; and another tech had replaced it with a nondescript "Zebra" humbucker. This gave rise to a new problem, though, as the Zebra was way too powerful, and completely overwhelmed the stock Yamaha neck humbucker.

Nondescript "Zebra" Humbucker

Now, Izzat had recently acquired a used Gibson humbucker. Might it be a better match for the Zebra than the stock Yamaha humbucker? With this in mind, we proceeded to measure the DCR of all three pickups. Our readings indicated that neither the Yamaha [9.08K] nor Gibson [8.06K] would be a suitable match for the Zebra [16.36K]. The only solution, then, would be to discard the Zebra, install the Gibson [8.06K] in the neck position, and relocate the Yamaha [9.08K] to the bridge.

Zebra Humbucker DCR - 16.36K

Gibson Humbucker DCR - 8.06K

Yamaha Humbucker DCR - 9.08K

The Zebra was desoldered and removed without much difficulty, but the Yamaha was another story. The bottom two pickup ring screws were frozen in place, and the heads were so rusty that there was no way to remove them with a screwdriver. Thank goodness I was able to remove the pickup itself, leaving the ring in place.

Then, using careful taps with my smallest chisel, I was able to dig into the wood and pry out the two screws from the side. This, however, left two gaping holes. The obvious solution was to plug them with dowels, wood dust and super glue; and recoat any bare areas with conductive shielding paint.

Damaged Pickup Ring Screw Holes Plugged

Another point of interest was that while installing the Zebra, the tech responsible had modified the stock control configuration of Neck Volume/Bridge Volume/Master Tone to Master Volume/Neck Tone/Bridge Tone. Izzat preferred this new configuration; and requested that it be retained. "Okey dokey," said I.

And so, the AES620 was rewired as per Izzat's specs using three Alpha A500K Long Shaft pots, an Epiphone three-way toggle switch; and new barrel jack. Caps of differing values were installed, 0.015uF for the neck and 0.022uF for the bridge.

Epiphone Toggle Switch Wired In

Epiphone Toggle Switch Installed

Alpha Pots and Barrel Jack Wired In

Electronics Upgrade Completed

Meanwhile, the AES620 was also stripped of all hardware so that everything could be cleaned, derusted and serviced. Parts too far gone to be saved were simply replaced. The fretboard was cleaned with naphtha and reconditioned with lemon oil; while the frets were degrimed and polished. Last but not least, the trio of ill-fitting set screw dome knobs was replaced with white transparent speed knobs.