Ground problem - doctors needed

[mr.sibs]

I am hoping one of the more techy among you can help me, I have tried a few things that don't seem to be working, and I consistently have a grounding issue causing lots of humming and buzzing.

I have rewired this circuit (which was buzzing before) with all new parts, following the fender guide for an elite below. I have a foil backed pickguard and I am sure I followed the guide as supposed, but I still get the buzzing which clicks as you touch any of the parts. Can you see anything that looks wrong? What would be the best test to find the problem (I have a multimeter)?

Apologies for the sh*t picture

[attachment=60798:basscircuit.jpg]

the bridge is grounded to the control, each green wire comes from the pickup and is grounded to the relevant controls. The red wires are hot wires from the pups. The capacitor is cut off on the pic but the tone is doing it's job.

[attachment=60799:pickupdiagram.jpg]


I admit I don't know what 18 is in the pic above, I have the rest of the circuit as displayed

[Ou7shined]

It looks to be as per the diagram right enough. You could perhaps do with trimming down your cap's length a bit so you can eliminate the possibility of it touching something it shouldn't once you got the control plate all screwed down.

18 is some sort of body earth.

Do you have dimmer switches or fluorescent lighting near by?

Edited October 7, 2010 by Ou7shined

[mr.sibs]

So should I be earthing the foil from the pickguard to one of the pots if 18 would ususally be for shielding? Am I missing grounding the pots too each other? I thought the foil eliminated the need for this

will try in some different rooms.

does it make a difference if the strings/neck are off?

Thanks all!!

[Ou7shined]

It is usually assumed that the part of the pot casing that touches the control plate or in this case the pickguard shielding is taking care of earthing it.
If you want to do an effective shielding job you should consider lining the entire cavity.

[BOD2]

Use your multi-meter to check the earth continuity.

Attach one probe to the earth side of the jack socket and then touch the other probe at various parts of the controls that should be earthed. Check the pot shells all have good earthing. In particular check that the bridge itself has a good earth connection - one probe on the bridge and the other on the earth of the jack socket.

If the pot shells aren't earthed then run a wire from a good earth point to one pot shell then daisy-chain a wire to each other pot shell. The foil screen should earth all the pots together but sometimes the foil breaks.

If the bridge isn't well earthed then unscrew the bridge and inspect the wire that comes up through the body. Splay the ends of this wire and rub the underside of the bridge with a sandpaper to remove any oxide layer to give a good connection. A little vaseline (has to be vaseline as this is conductive) on the underside of the bridge where the wire touched can sometimes help.

But always use the multimeter to check your connections are good.

[mr.sibs]

[quote name='BOD2' post='981629' date='Oct 8 2010, 02:34 PM']Use your multi-meter to check the earth continuity.

Attach one probe to the earth side of the jack socket and then touch the other probe at various parts of the controls that should be earthed. Check the pot shells all have good earthing. In particular check that the bridge itself has a good earth connection - one probe on the bridge and the other on the earth of the jack socket.

If the pot shells aren't earthed then run a wire from a good earth point to one pot shell then daisy-chain a wire to each other pot shell. The foil screen should earth all the pots together but sometimes the foil breaks.

If the bridge isn't well earthed then unscrew the bridge and inspect the wire that comes up through the body. Splay the ends of this wire and rub the underside of the bridge with a sandpaper to remove any oxide layer to give a good connection. A little vaseline (has to be vaseline as this is conductive) on the underside of the bridge where the wire touched can sometimes help.

But always use the multimeter to check your connections are good.[/quote]

Thanks, silly question, but what setting should I use on the multimeter? The Diode setting?

Help very much appreciated

[BOD2]

[quote name='mr.sibs' post='981731' date='Oct 8 2010, 04:21 PM']Thanks, silly question, but what setting should I use on the multimeter? The Diode setting?

Help very much appreciated [/quote]

That's not a silly question.

But the answer depends on your multimeter. Some have a "continuity test" setting with a beeper that will make a noise when you touch the two probes together. If you don't have that then use the "resistance" setting - set to the lowest range.

On this setting, when you touch the two probes together you should get a reading of zero. When checking your earth connections you should be looking for a reading of zero (or very nearly zero) between the earth connection of the jack and any earthed point, since what you are measuring is essentially just the resistance of a piece of wire between these two points.

[mr.sibs]

[quote name='BOD2' post='981750' date='Oct 8 2010, 04:44 PM']That's not a silly question.

But the answer depends on your multimeter. Some have a "continuity test" setting with a beeper that will make a noise when you touch the two probes together. If you don't have that then use the "resistance" setting - set to the lowest range.

On this setting, when you touch the two probes together you should get a reading of zero. When checking your earth connections you should be looking for a reading of zero (or very nearly zero) between the earth connection of the jack and any earthed point, since what you are measuring is essentially just the resistance of a piece of wire between these two points.[/quote]

Brilliant, there is a beeper, so I will try that and if not then I understand on the resistance, thanks

[Subthumper]

Hi, its difficult to see from the picture but are the wires that come from the pickup shielded or two seperate wires (usualy red and black)? if its two seperate wires make sure they are twisted together, this will prevent alot of hum and buzz. If they are shielded types then you have another problem so as amentioned check all your earthing connections.

[mr.sibs]

[quote name='Subthumper' post='981915' date='Oct 8 2010, 07:11 PM']Hi, its difficult to see from the picture but are the wires that come from the pickup shielded or two seperate wires (usualy red and black)? if its two seperate wires make sure they are twisted together, this will prevent alot of hum and buzz. If they are shielded types then you have another problem so as amentioned check all your earthing connections.[/quote]

They are both dimarzio pickups which have in turn - a red for hot (you can see these soldered above to the central pole of each vol pot) a green which is ground (soldered to the relevant back of pot) and a balck and white wire which are twisted and soldered together then wrapped with electrical tape. Is this correct? I am not sure about shielding further than this

I tried the multimeter this morning and all components seem to be consistent with levels of resistance in relation to each other, i tried pots, bridge, jack. So I may now try the cooper shielding and just put her back together!

Thanks

[Subthumper]

[quote name='mr.sibs' post='982305' date='Oct 9 2010, 09:35 AM']They are both dimarzio pickups which have in turn - a red for hot (you can see these soldered above to the central pole of each vol pot) a green which is ground (soldered to the relevant back of pot) and a balck and white wire which are twisted and soldered together then wrapped with electrical tape. Is this correct? I am not sure about shielding further than this

I tried the multimeter this morning and all components seem to be consistent with levels of resistance in relation to each other, i tried pots, bridge, jack. So I may now try the cooper shielding and just put her back together!

Thanks[/quote]


Looking at the pic the body of the pots are'nt connected together. They are relieying on the foil on the back of the control plate and sometimes this isnt enough. Wire them together. Afraid earthing is a bit of a never ending subject. You could do a degree in it and someone will still argue the toss or something wont work. Also try soldering a wire to the jack earth and touching it on various other parts that should be earthed to see if the hum/buzz dissapears. One other thing, have you tried it with a different amp? Make sure that isnt the problem.
Good luck
Cheers Just