Metal pickup covers earthing out

[rhythmthief]

I've got one of these ...

... which I've just rewired in series, with phase switches for each pickup, according to this wiring diagram (third picture down in the link) only without the middle pickup.
treblebooster.com/brian_may_pickup_mod.htm

While it sounds great and everything seems to work as it should, I've noticed today that when the strings touch the metal cover of the bridge pickup, the signal disappears. This happens no matter what position the pickup on/off switches or phase reversal switches are in. It doesn't happen with the neck pickup, which is wired in exactly the same way. Neither pickup cover is permanently earthed. Does anyone have any ideas what might be wrong here, before I strip it down and have a look inside?

[rhythmthief]

Mar 19, 2013 11:29:22 GMT -5 rhythmthief said:

This happens no matter what position the pickup on/off switches or phase reversal switches are in.

Not strictly true, as it turns out ... if the bridge pickup phase switch is not thrown, the signal does not cut out, although there is a small drop in volume. Personally, I suspect the problem is in my wiring of that switch - I'm not a very experienced solderer! - but would be interested to hear more informed opinions before I open it up again.

[JohnH]

seems that the pickup cover becomes 'hot'. Could you step through all combinations of your switches to see if this happens, it may give a clue.

John

[ashcatlt]

Do the covers have a separate wire of their own, or are they sharing the "bottom" coil wire?

[b4nj0]

I seem to recall that you have to lift the pick up cover's ground lead and move it to another location if you are doing the Tele four way switch mod. This mod gives the series option. I reckon that's your problem here. It shouldn't take long to google the 4-way Tele mod to confirm?

[rhythmthief]

Thanks folks. I don't think the pickup covers have a separate ground lead. The problem seems to happen only when the bridge pickup is operated in "phase reverse" mode, ie when the negative lead becomes the positive and vice versa. The problem does not occur with the neck pickup.
I think I'll open it up again and take the bridge pickup phase switch out of the circuit and see if the problem's still there with the bridge pickup wired directly to its on/off switch. I'll keep you posted ...

[ashcatlt]

If what we think is happening is actually happening, then you should also lose the neck pickup when in normal (in phase) series mode. Didn't you say that volume is reduced in that case? It should also be a bit noisier with bridge only if you flip the phase switch.

You could diagnose with a meter across the cable, but I'm pretty confident that this is the issue. It's most likely not in the switching itself, but in the fact that the cover is sharing a wire with the coil. The pickup cover needs to be separated from the coil wire. This will probably mean some rather delicate surgery. First you need to open the cover and remove that connects to it, then add a separate wire.

[rhythmthief]

Right, I've pulled it to bits, removed the pickup covers and can now see that they ar eindeed earthed as part of the circuit. I've run out of time tonight - off to work soon - but tomorrow I'll earth the covers to the back of the volume pot and put it all back together. I'll be replacing the bridge pickup phase switch with a series/parallel switch as I think that'll be more useful and it's what I should have done in the first place. Thanks for your help people, this is a great froum!

[rhythmthief]

Just to finish this off for anyone who's interested ... the pickups are now earthed independently to the back of the volume pot. I wired in a series/parallel switch, but for some reason it didn't work as it should, and I realised that the parallel setting would just sound hopelessly feeble next to the rather frightening sounds this guitar can now kick out. So I went back to the two phase switches. Everything now works as it should and it sounds amazing! Thatnks for your help everyone, I'll no doubt be back when my next project runs into problems ...