Monday, August 19, 2013

'62 Strat pickup repair

This morning I had in my shop a bridge pickup from a 1962 Fender Stratocaster.  The pickup was not producing any sound when installed in the guitar and when hooked up to a mulitmeter, showed no resistance.  This means that there is an open circuit somewhere between the positive and the negative lead wires.  It is important to be very careful when working on this type of vintage gear in order to preserve the original tones of the guitar, so a number of steps were taken to carefully diagnose the source of the problem.

First, upon removing the cover I could see that this pickup uses Formvar wire, a common wire of the period, which gives it that coppery look.  There is a thin layer of wax on the pickup meaning it was at some point wax potted.

I could see that the wire leading to the black, negative wire is leading to the center of the bobbin and the wire leading to the white, positive, wire is coming from the outside.  This means that the wire was wound onto the pickup in a clockwise direction. If you point your finger at the left eyelet where the black lead wire is connected and then follow the wire on a path around the magnetized poles about 8,000 times and then end at the right eyelet you can see that this pickup was indeed wound in a clockwise direction.

When I oriented a magnetometer over the poles I could see that this pickup is South up with an average of 27 gauss.  A bit too much magnetism for a bridge pickup for my taste, but in the interest of preserving originality I left the magnets alone.

Next I inspected the condition of the actual Formvar wire and I could see that there was no visible damage.  My next step was to heat up the solder on the eyelets and add a little bit more solder.  This connection can get dirty over the years and cause a bad connection.

Eureka!!  After doing that I tested the resistance again and sure enough this pickup is reading about 5.44 thousand ohms of resistance, just right.  I am done and the original tone of the pickup is preserved.

If heating up the eyelets had not worked my next step would have been to disconnect the finish and unwind a few coils to try to find a break.  As a last resort I would have removed all of the old wire and solder, rewound the pickup with vintage-spec wire and waxed it.