How to test electronics for problems

[Quagmire02]

I wired a fender pickguard with DiMazio HS-3s and it seems that I have a ground problem.

When I plug in, I get insufferable buzzing hum. If I touch the jack plate with a finger, the hum stops totally. Touching the bridge also affects it, making it worse sometimes and better others. I have grounds soldered to the bridge and jack.

I'm wondering what the easiest way is to detect where I've gone wrong. The pickup wiring worked ok in another guitar...

Is there a troubleshooting method that anyone can give me?

 

[ggunn]

I wired a fender pickguard with DiMazio HS-3s and it seems that I have a ground problem.

When I plug in, I get insufferable buzzing hum. If I touch the jack plate with a finger, the hum stops totally. Touching the bridge also affects it, making it worse sometimes and better others. I have grounds soldered to the bridge and jack.

I'm wondering what the easiest way is to detect where I've gone wrong. The pickup wiring worked ok in another guitar...

Is there a troubleshooting method that anyone can give me?

what it sounds like to me is either you have an open ground or ground and hot reversed somewhere.

 

[Quagmire02]

what it sounds like to me is either you have an open ground or ground and hot reversed somewhere.

how do I check for an open ground?

 

[ggunn]

how do I check for an open ground?[/QUOTE

Here are a couple of simple tests:

Plug a known good cable into your guitar. Turn up all the volume and tone pots. With a meter check the resistance between the tip and sleeve at the other end of the cable. You should see the resistance of whatever pickup(s) you have selected. If you see no load, then you have an open ground or some other break.

With the cable still plugged in, check the resistance between the tip of the cable and the back of one of the pots (usually the ground terminates there). Again, you should see the resistance of whatever pickup(s) you have selected; if you see a zero or very low resistance, you have a hot-ground reversal somewhere in your wiring.

Good luck.

 

[Quagmire02]

Thank you.

 

[Anfontan]

I had the same problem last month after changing the pickup in one of my guitars, it turned out that the 3rd lug on the volume pot should have grounded to the chasis of the pot. It had became a cold solder joint, once resoldered all is fine.
Bet you have the same problem.

 

[Quagmire02]

I had the same problem last month after changing the pickup in one of my guitars, it turned out that the 3rd lug on the volume pot should have grounded to the chasis of the pot. It had became a cold solder joint, once resoldered all is fine.
Bet you have the same problem.

Could you explain in moron terms what that means specifically? Thanks! I'm capable of following schematics, but I don't understand much of the fundamental logic and terminology of electronics.

 

[apl]

If I touch the jack plate with a finger, the hum stops totally. Touching the bridge also affects it, making it worse sometimes and better others. I have grounds soldered to the bridge and jack.

Sounds like you don't have a good connection between the bridge and ground. Touching the bridge or strings should have the same effect.

But humbuckers shouldn't hum very much at all, even in front of a monitor.

Weren't you gonna have someone who knows what they're doing take a look at it?

 

[Quagmire02]

Sounds like you don't have a good connection between the bridge and ground. Touching the bridge or strings should have the same effect.

But humbuckers shouldn't hum very much at all, even in front of a monitor.

Weren't you gonna have someone who knows what they're doing take a look at it?

Yeah, I'm going by a shop today to let someone check it out. I can't leave it there since the guy's booked for the next 10 weeks. I'm hoping he can nail the problem in like 15 minutes.

It's quite possible that I have a cold joint somewhere. I don't know how to identify them, however.

 

[apl]

The more I think about, I'm convinced that your pups are wired wrong. Each pup should have a red, green, black, white and naked wire. Each pup's black and white wires should be soldered together and the joint taped or shrink wrapped. The green and naked wires should all be soldered to a ground point. The red wires should all go to different positions on the switch. Here's how the red wires go: http://www.stewmac.com/shop/Electro...Stratocaster/Instructions/I-3192.html#details

 

[Quagmire02]

The more I think about, I'm convinced that your pups are wired wrong. Each pup should have a red, green, black, white and naked wire. Each pup's black and white wires should be soldered together and the joint taped or shrink wrapped. The green and naked wires should all be soldered to a ground point. The red wires should all go to different positions on the switch. Here's how the red wires go: http://www.stewmac.com/shop/Electro...Stratocaster/Instructions/I-3192.html#details

I think I checked the wiring against the schematics that DiMarzio provides for four-conductor pickups and it seemed fine. Did you check out the pics i posted in the other thread

 

[apl]

I think I checked the wiring against the schematics that DiMarzio provides for four-conductor pickups and it seemed fine. Did you check out the pics i posted in the other thread

Took another look at the pix. Can you check that the black/white connection at each pup is good? Maybe they were just twisted together and taped and maybe the connection's not good. They need to be soldered.

And as I mentioned above, touching the bridge should be exactly like touching the jack, unless you've got a bad connection between the two.

 

[Quagmire02]

Took another look at the pix. Can you check that the black/white connection at each pup is good? Maybe they were just twisted together and taped and maybe the connection's not good. They need to be soldered.

I'll double check. They are taped down to the foil with electrical tape.

And as I mentioned above, touching the bridge should be exactly like touching the jack, unless you've got a bad connection between the two.

touching the jack totally stops the hum. touching the bridge doesn't, just changes it a bit. if I touch the jack with my pinky and put my hand on the bridge, it starts humming/buzzing again.

 

[apl]

I'll double check. They are taped down to the foil with electrical tape.

There should be no connection between those and the foil.

touching the jack totally stops the hum. touching the bridge doesn't, just changes it a bit. if I touch the jack with my pinky and put my hand on the bridge, it starts humming/buzzing again.

Can you verify that the wire from the bridge to ground is not getting on the hot side somewhere? Maybe a pinch point or something?

 

[Quagmire02]

There should be no connection between those and the foil.

I'll have to double check to make sure they are not touching the foil.

Can you verify that the wire from the bridge to ground is not getting on the hot side somewhere? Maybe a pinch point or something?

It's the thicker black wire in the pictures...