Trouble-shooting a BL L-500XL pickup...

[quarry]

OK guys, I think I need some help on this one...


Elsewhere here, I posted about re-wiring a Kay ES-335 copy.
First, I merely removed the stock bridge PU and replaced it with a Bill Lawrence L-500XL (as requested by the client). All turned out good, til the client returned it to say there was no output from the 500XL!!!

I decided to pull out the entire electronics, and rewire. I did so, using the standard Epi Sheraton II diagram as a guide.

The 500XL still had to output. So I wired the 500 directly to the output jack, and still nothing!

I cut the cable from the pickup, and re-dressed the wires, and tried again (in case the wires were broken, etc) still no output.

I can't imagine the 500XL can just die??? Anyone got any ideas what else I can try?

BTW - I absolutely KNOW I did have output before I returned it to owner the first time! I remember thinking how trebley and thin the pickup actually sounded - nothing like what I was expecting (since this is supposed to be the "Dime Bag Darrell" pickup). And I adjusted the PU height to get the bridge and neck volume levels fairly even...


Other tidbits: I used brand new 0.022uF caps, and tested all four 500K pots (they all checked out!).... New 22 gauge wires... and a new output jack...
The switch is the original, but tests out OK.... (I used it in another circuit, and it switched fine)...

When testing the PUs directly to the output jack, I used test leads with alligator clips on them to temporarily connect the leads...

Extra resources:

The L-500XL wiring diagram:





The Epi Sheraton wiring diagram:

[ChrisK]

Measure the resistance from the Red wire to the Black wire.

Measure the resistance of the bare wire to the Red and to the Black wires.

What are they? ("Nothing" is not a permissible answer, it's 0, something Ohms, or over range.)

While you're at it, measure the resistance from the Red wire to the Green/White junction. Measure the resistance from the Black wire to the Green/White junction.

[quarry]

ChrisK, thanks for the reply. Here are the Ohm meter results...

S= bare, outter sheilding
B= black wire - ground
G= green wire (used for coil splitting)
W= white wire (used for coil splitting)
R= red wire - hot lead

S - R = infinite
S - G = infinite
S - W = infinite
S - B = zero
R - G = infinite
G - W = infinite
R - W = infinite

This does not look good to me. But I await your opinion...

[ChrisK]

S - R = infinite, Good, no shield short
S - G = infinite, Good, no shield short
S - W = infinite, Good, no shield short
S - B = zero, Hmmm, this should be infinite

R - G = infinite, if R - G is a coil, it is open (bad)
G - W = infinite, if W - G is a coil, it is open (bad), if it is a wire from each coil, it is a good thing (not shorted)
R - W = infinite, if R - W is a coil, it is open (bad)

R - G and R - W pretty much covers the coil with the red wire. It is open and hence is bad. G - W from your drawing appears to be a wire from each coil, and a reading of infinite is good (when they're not joined).

Where is R - B?

Per your drawing;

R - G is a coil, it measures open and is bad.

W - B is a coil. Since S - B read zero and S - W read infinite, it measures open and is bad.

This does not look good to me.

For these to be open, either the pickup cable was pulled on and wires in the pickup were broken, or enough current was caused to flow through the coil to burn out the wires like a fuse.

AWG, I actually DO fill my head with this stuff since knowing the models is key. Many years ago, stranded in a desolate place, finding a spool of 16 gauge hookup wire and an Edison screw-in house fuse base (and a house fuse), I was able to effect electrical repairs to a car's cooling system (fusible link as well), and escape. There was no cellular connectivity, heck they'd just been invented. There wasn't a telephone either.

Rule of thumb (well, logarithms). A 12 gauge wire is good for 20 amps. Each 10 gauges indicates a reduction of a factor of 10 in current carrying capability. From 12 gauge to 42 gauge is 30 gauges or 10^{^3} in current reduction. 20 / 1,000 =20 mA.

If each coil was 5,000 Ohms, one would have to develop 100 Volts across each coil to cause this current to flow. However, since most wire turns are not open to the air, less current might cause damage. After all, 100 volts and 20 mA is 2 watts, and after a while, damage could well happen.


Either the pickup cable was pulled on or high voltage was presented to the jack, either in the form of an amp failure or a significant energy voltage transient.

Was it connected to a home-made amp?

[quarry]

Don't know if this is of interest to anyone, but I finally found the true cause to my "fried" 500XL...

Just check out these pictures. I noticed this as I was replacing the pickup with the new 500XL I just got in the mail...



Hmmmm.... that's interesting! They bored the wiring hole right in the path of the pickup cover screw hole!
I wonder if the screw was long enough to actually touch the wiring???



OMG! Lookie there... a puncture hole! Who'da thought?!?!

Guess I'll be grinding one pickup cover screw down an eighth of an inch or so.....

[ChrisK]

Oh, so the pickup wasn't broken of damaged, just screwed? ;D ;D

These puzzles are a lot easier to diagnose when you actually disclose all of the clues!


Now, a conundrumium has arisen; either that screw caused several open circuits in the wire (anti-shorts - hmm, must have been an insulating screw), your measurement skills are way questionable (you measured open on all but one readings), your test leads are screwy, or you didn't actually find the problem (just maybe the cause).

Maybe, the screwed cable was anchored and the pickup was tugged on, thus breaking the wires.

[newey]

We'll add this to the list of "things you'd never think could go wrong but did . . " Assuming, as ChrisK points out, that this was at least the instigator of the problem.

If so, I'd say that the illustrious Mr. Murphy was not only in the house, he had the Gold Circle seating.

[cynical1]

Years ago in another life I worked for the phone company. Nails and screws where the two biggest offenders in bad or erratic connections. Rats came in a close third, but that's another story...

Good catch.

Happy Trails

Cynical One