Earth hum when touching pickup

musicalstash

Recently bought used epiphone but has a hum issue.

When either of the pickups are touched there is a hum which only goes away when the back of the pots or earth on the jack is touched. 

The previous owner did  the rewire when he installed a set of p90 style pickups. 

Is it possible to tell what's wrong from the photos to save from desoldering and starting again..

https://ibb.co/dMjYyG7

https://ibb.co/k0w6xZr

Funkfingers

Fark!

In the words of Edwyn Collins, "rip it up and start again."

I suspect that there is some ugly shit lurking underneath the capacitors.

musicalstash said:

The previous owner did  the rewire when he installed a set of p90 style pickups. 

What pickups are in the guitar now? Soapbar P90s, humbucker-sized P90s, covered humbuckers or open bobbin humbuckers?

ICBM

The pickup covers aren't grounded. It would be useful to remove the black tape and see if the red or white wires are connected to the cable shields.

It's also possible that the strings aren't grounded - does the buzz stop when touching the strings?

Funkfingers

ICBM said:

The pickup covers aren't grounded.

Being plastic, soapbar P90 covers would not require grounding. Metal covered humbucker-sized P90s would be a different matter.

prowla

prowla

I don't see a Gnd wire running to the bridge.
Regardless of the plastic cover, do the P90s have a metal base?

The soldering is as cack-handed as mine tends to be.

Using red for Gnd is something I don't see very often; it hurts my eyes trying to follow wiring.

What's that dangling white wire between the selector switch and the pots?

musicalstash

Thanks for comments.   Should have mentioned the P90s are in chrome humbucker size covers ,.  There is no earth lead to the bridge (there is no routing in the body).  I have ran a wire to the bridge from the pickups it makes no difference. 

No hum when I touch the strings or bridge, will look under the tape but the wiring diagram online only shows two wires from the pickup.

The dangling white wire is because it looks as though the previous owner had only 2 core wire to hand (the blue earth wire)...

Thanks again 

Funkfingers

prowla said:

The soldering is as cack-handed as mine tends to be. … it hurts my eyes trying to follow wiring.

It certainly hurts trying to follow the wiring in the OP's photographs.

Most of the soldering on display is completely unnecessary.

When changing from humbuckers to HB-sized P90s, the only solder joints that need work are the inputs to the volume pots and the ground connections. In an ideal world, the metal covered P90s would have 2-conductor + shield output cable - enabling phase reversal.

My guess is that the previous owner has attempted the "Fifties Wiring" mod and a snake oil capacitor upgrade.

Funkfingers

Looking at the second photograph, the neck pickup tone control has two signal sources connected to terminal 3. The "leg" of the capacitor and a white conductor inside the blue insulation. (The latter disappears into the mess of insulation tape, connecting to who knows what?) One of these connections is redundant. My money is on the white wire.

ICBM

Just a bit of random pedantry now I’ve come back to this… the problem is *not* “earth hum” - although that seems to be the nearly universal description for any unexplained hum or buzz.

Firstly it is not hum, it’s buzz - they’re different-sounding and have different causes. Secondly it’s not caused by anything to do with earthing. Earth loops - which produce hum - occur between two pieces of mains-powered equipment.

It’s actually buzz being picked up by lack of, or incorrect, shielding or grounding.

Sorry for the pedantry - it’s just that it’s often easier to solve a problem if you describe it correctly .

The very first thing to do is remove that mess of tape and see what’s under there, it may explain everything at one go.

musicalstash

ICBM said:

Just a bit of random pedantry now I’ve come back to this… the problem is *not* “earth hum” - although that seems to be the nearly universal description for any unexplained hum or buzz.

Firstly it is not hum, it’s buzz - they’re different-sounding and have different causes. Secondly it’s not caused by anything to do with earthing. Earth loops - which produce hum - occur between two pieces of mains-powered equipment.

It’s actually buzz being picked up by lack of, or incorrect, shielding or grounding.

Sorry for the pedantry - it’s just that it’s often easier to solve a problem if you describe it correctly .

The very first thing to do is remove that mess of tape and see what’s under there, it may explain everything at one go.

Issue did turn out to be under the tape, there was a ground wire from each pickup wrapped up in it- not too sure why didn't use it  .  All sorted now, thanks