CA Guitar Repair Blog: Fender MIJ ST72-55 Overhaul

Evaluating the Electronics

Electronics-wise, there's certainly something not quite right with this ST72-55. I did put the guitar through its paces prior to disassembling it, and noticed that in all switch positions and even with the volume and tone knobs full on, the output was lifeless and muffled. In short, this ST72-55 does not sound anything like a typical SSS Fender Stratocaster.

With the volume and tone knobs popped off, it's evident that at least one of the pots has been replaced. All three pots feature split knurled shafts, but that's where the similarity ends. While the volume pot has 18 splines, Tone Pot 1 [neck] and Tone Pot 2 [middle] have 24 splines.

A Mix of Gotoh and CTS Pots

Upon unscrewing the pickguard, it's quite obvious that the electronics in this ST72-55 have been "modified" to a fair extent, for want of a better term. It's nice to see that a previous owner has taken the trouble to install aluminum foil shielding in the body cavities as well as on the back of the pickguard.

Aluminum Foil Pickguard Shielding

Aluminum Foil Pickup Cavity Shielding

Aluminum Foil Control Cavity Shielding

The most obvious non-original components are the large tone capacitor and CTS pots, most probably someone's idea of an "upgrade." While the electronics are generally badly tarnished and in dire need of servicing, the PCB-based five-way pickup selector switch has it the worst, with rust clearly visible on the blade and metal housing. Considering all this, as well as the substandard soldering and gnarly wiring; it's no wonder that this Strat sounds anything like one.

A Trio of Ceramic Single-Coils

Closer View of the Electronics

Rusty Pickup Selector Switch

Switch Lugs and Wiring

Gotoh B500K Volume Pot

Gnarly Volume Pot Wiring

Tone Pots and Capacitor

Tone Pot 1/Neck - CTS 250K

Tone Pot 2/Middle - CTS 250K

MIJ Output Jack and Wiring

Replacement Parts

As one might expect, Pak Long is not all all happy with the current state of his guitar's electronics. At least, however, he now knows why his ST72-55 has sounded peculiar all these years. I'm pleased to say that he's approved my proposal to replace and upgrade a number of components. These upgrades include a Switchcraft #11 output jack, a Mallory 150M 0.022uF capacitor, a Gotoh DM-50 five-way selector switch, Alpha A250K pots, pickup height screws and tubing, stainless steel pickguard screws, and also a full rewire with Vintage Push-Back Wire.

Switchcraft #11 Output Jack

Mallory 150M 0.022uF Capacitor

Gotoh DM-50 Five-Way Selector Switch

Alpha A250K Pots

Vintage Push-Back Wire

Pickup Height Screws and Tubing

Stainless Steel Pickguard Screws

Volume and Tone Knob Problem

The inner splines of the current volume and tone knobs are virtually non-existent. It's almost as if someone had deliberately scraped them off, and then forced the knobs onto the Gotoh and CTS pot shafts. If this be the case, do lend me your ears for a minute. Folks, I do not condone this "DIY shortcut" at all. Scraping off the inner splines alters the knobs permanently, for one. And as for forcing the knobs on, the pressure exerted might very well damage the pot wiper and resistive track; and you'll end up having to replace the pot in question.

Current Knobs - Damaged Inner Splines

I've tried fitting these knobs onto brand new CTS and Alpha pots, but to no avail. At best, I've been able to push them halfway down the shaft, but no further. And, in case it crossed your mind, forcing them on is never an option. The good news is that I tried a set of unused 18-spline knobs, and they fit nicely on the Alpha A250Ks. So you see, it's worth the extra effort buying the right set of knobs for your pots.

Will Not Fit a CTS Pot

Will Not Fit an Alpha Pot

18-Spline Replacement Knobs

Fits an Alpha A250K Pot Perfectly

Pickup Issues

I do admit, the three single-coil pickups are cruddy and the plastic covers need to be given a good scrub with soap and water, as my late Mama would say. And they will, believe me. However, what really troubles me are the exposed coils and brittle black and white pickup leads. Besides being cut a wee bit short, they could snap off at any point without warning. There's also the issue of dull solder joints for the hot and ground leads. These might actually be cold, and one day totally fail.

Middle Pickup - Brittle Leads

Dull Solder Joints

What are we going to do, then? Well, for starters, let's wrap those exposed coils in pickup coil tape. This should keep them safe and sound for a long time yet. We'll also desolder those brittle plastic-coated leads and replace them with Vintage Push-Back Wire leads. And while we're at it, let's use yellow for the middle pickup hot lead, just to differentiate it from the neck and bridge. Sounds like a plan!

Covers Taken Off - Exposed Coils

Coils Wrapped in Pickup Coil Tape

Black and White Leads Desoldered

Vintage Push-Back Wire Leads Installed

Wiring in the Pickups and Replacement Electronics

With the pickups sporting brand new leads, let's now install them into the pickguard, and wire them to the replacement switch and pots. Do take note that Tone 1 is connected to the neck pickup, and Tone 2 to the bridge, leaving the middle pickup "wide open."

Pickup Height Screws and Tubing Installed

Pickups Installed

Pots and Switch Installed

Pickups and Electronics Wired In

Closer View of the Pots and Switch

Following this, we'll solder the leads to the output jack and tremolo claw; completing the circuit. The final step will be reattaching the pickguard with those brand new stainless steel screws, and checking to see if everything works.