I've been scratching my head for some time now trying to work out how the pickup switching works in my JTV-89,
mainly because, although I like the pickups, I wanted to have more options on the magnetic side.
I wanted something like what I would want on a HSH strat.
That is: two 4conductor humbuckers with duncan triple shots and a single coil sized humbucker in the middle.
The switch, as it is, doesn't give any option to add another pickup, because all four (well, five) conductors are
soldered on a small PCB that's attached to the selector and it's impossible to see inside the selector to find
some way to add anything or change any of the pickup/coil settings, so... I went and opened it.
Well, I didn't exactly open the one inside my guitar, but a spare I got from the spanish distributor.
The switch was failing and I didn't want to send the JTV to tech service because they are sluggish, so I asked them
for a replacement switch and they sent it, on the condition that the guitar would be serviced at the store where
I bought it. In fact, they did send the wrong switch the first time, so I ended up with two, one that seems to belong
to a JTV-69 and the one I needed.
I've been a customer for a long time, so the people at the store agreed to let me change it myself, which I never did,
because once I bought a hardcase for the guitar, the switch stopped failing so often (It almost never fails now and
I've worked out a way to quickly get it back to normal).
So I opened the selector and found out how it works.
It works in the same way a superswitch would, only this one is preset. There are fixed contacts and mobile ones.
The fixed ones are printed in a way that does the coil splitting in positions 2 and 4 and does, well... you know...
what a JTV-89 does with its mags :-)
The switch is some kind of 2P5T, where on one pole you select the magnetic pickup setting and on the other
you select modeling pickup setting. On the modeling side, the contacts are arranged in a standard fashion.
Bad news first:
The modeling side of the switch has three resistors (18,65k, 75,1k and 37,2k are the exact values, though
they most likely correspond to standard values of 18k, 75k and 36k) and I'm guessing the variax brain detects
which position the selector is on based on the resistance measured between the two contacts that go out the PCB.
Good news: The values of those resistors are standard and they are possible to replicate, so you can use a
standard two pole five throw blade selector and add another pickup (or whatever you want to do with your five)
Better news: The lower PCB can be desoldered from the selector and soldered to a different one, so you don't
have to mess around with resistor values and provide some new small board to solder them onto.
YES!! I know I should include pictures in this very post, and at this very moment, but my camera is out of battery
and my phone isn't good enough, so you'll have to wait, but the pics will come.
I won't actually modify the guitar until the triple shots and the duckbucker are here, then I will have a friend route
the guitar for me and then I will do the electronics so, for now, the only pics I'll post are the ones of the selectors.
In a month or two (when I can buy the stuff) I'll start doing the mods