Think the bridge ground wire has disconnected on my Harley Benton SG Custom

Dave_Mc · May 26

Hi everyone,

I think the bridge ground wire isn't connecting any more on my Harley Benton SG Custom- I'm getting a loud hum (which disappears when I press the instrument cable in tight- it does this on other guitars too, except it's not as loud hum and it also disappears so when I touch the strings!), and I tested continuity and I'm not getting any continuity between the strings and the instrument cable ground. I'm getting continuity when I touch all the other metal parts and ground. I'm getting sound ok when I play the guitar, just the hum is the problem.

What's a bit strange though is that the bridge ground wire still seems to be connected to the bridge! Light tugging (I didn't want to pull any harder in case I did actually detach it) suggests it's still attached to something at the bridge/tailpiece. I've done a lot of pickup swapping on that guitar recently (I think the hum started with the first pickup change, though, and it was slightly worse or slightly better with some pickups than others, but still always there), so I also snipped the bridge ground wire (in case I'd broken/melted it) and stripped it back an inch or two, but I'm still getting no continuity even when I connect the multimeter to the strings and the end of the bridge ground wire. (Of course, I could have broken or melted the bridge ground wire before where I stripped it!)

Any ideas? I've read that a backwards-wired jack socket can sometimes cause the hum, but (and I could be wrong here) presumably that wouldn't affect continuity from the strings to the bridge ground wire? I didn't try rewiring the jack socket (I haven't touched the jack socket's wiring), but I did take it out for a quick look and it looked to me like it was wired correctly (but I could well be wrong!).

It has gold hardware, could that be it? I've seen some Youtube videos where someone was saying that on some of the Harley Benton basses with black hardware, the bridge ground wire wasn't actually making electrical contact because of the bridge finish. But that wouldn't explain why it was working originally- unless it was a bit of an intermittent connection I guess.

I did kill what was originally the bridge volume pot (and IIRC the bridge ground wire was attached to it)- it may not have been actually broken, but after wasting too much time troubleshooting, I just put in another (working) old pot from another guitar of the same value/taper/size which was lying around and which was a quicker fix. (I've converted that pot to the middle pickup volume now, and moved the neck volume, as that suits me better since the bridge and neck volumes are now where they'd be on a 2-pickup Gibson-style guitar- I doubt this has anything to do with it, but I'm mentioning it just in case it does! The hum did start before I killed the old volume pot and put in the new volume pot and moved them around.)

Thanks for your help everyone,

Dave

ICBM · May 26

I assume you mean buzz and not hum

.

If you get continuity to all the other grounded metal parts but not to the bridge, tailpiece or strings, then the ground wire is not making contact even if it appears to still be trapped by the post insert. Gold plating makes no difference, gold is electrically conductive.

The absolutely correct way to fix it is to pull the post insert out of the body, make sure the wire is poked firmly down the hole alongside it, and drive it back in, but this can be tricky and there is a risk of damaging the finish. There's a decent bodge though, which is to drive a long and fairly thin self-tapping screw into the hole in the control cavity so the tip of it bites into the post insert, then wrap a wire tightly around it - if you can find one of the right length you can do it better with a terminal tag under the screw head, but it needs to be exactly the right length for that.

Dave_Mc · May 26

Brilliant, thanks John (as usual!)

ICBM said:

I assume you mean buzz and not hum .

I assume so! It's just like pretty loud "noise". It sounds a bit like a P90 when plugged into a high gain amp when you're standing too close to the amp.

ICBM said:
If you get continuity to all the other grounded metal parts but not to the bridge, tailpiece or strings, then the ground wire is not making contact even if it appears to still be trapped by the post insert. Gold plating makes no difference, gold is electrically conductive.

LOL I just assumed it was cheapo gold substitute! If it's actually gold, you're quite right, it's a really good conductor! D'oh!

ICBM said:
The absolutely correct way to fix it is to pull the post insert out of the body, make sure the wire is poked firmly down the hole alongside it, and drive it back in, but this can be tricky and there is a risk of damaging the finish. There's a decent bodge though, which is to drive a long and fairly thin self-tapping screw into the hole in the control cavity so the tip of it bites into the post insert, then wrap a wire tightly around it - if you can find one of the right length you can do it better with a terminal tag under the screw head, but it needs to be exactly the right length for that.

Bodge sounds like a better idea, this is me after all.

Some of the paint was getting a little flakey behind the pickups and pickup rings already, so I would guess there's a pretty good chance of damaging the finish, especially if I'm involved!

Any idea on the best thickness of the screw? I'll have to buy some so I might as well get the size which will work best. (When I get home I'll try to estimate roughly how long I need, probably safest to buy a mixed set of lengths just to be sure.)

Am I right in thinking that self-tapping are the ones which you don't have to drill for, you just screw them into the bare wood and they make their own hole? I'm guessing (can you tell I've never done this before?

) you put the screw slightly off to the side of the cavity leading to the bridge, and then screw the screw at a slight angle so it eventually meets the bridge ground wire cavity and touches the bridge inserts? Or do you want to avoid the other cavities completely? Or have I totally misunderstood and you actually put the screw into the bridge ground wire cavity and just follow the cavity to the bridge stud? (In which case I'm guessing the thickness of the screw depends on the thickness of the cavity?)

ICBM · May 27

Dave_Mc said:

Or have I totally misunderstood and you actually put the screw into the bridge ground wire cavity and just follow the cavity to the bridge stud?

Yes, exactly that - from the control cavity into the hole the wire now comes out of - you may have to remove the neck volume pot to get enough clearance. The size of the screw depends on the diameter of the hole, but probably about 3-4mm.

There’s a photo here somewhere, I think of a Les Paul Deluxe, where it’s been done already.

Aha, found it - https://imgbb.com/4mHXn3W

Dave_Mc · May 27

ICBM said:

Dave_Mc said:

Or have I totally misunderstood and you actually put the screw into the bridge ground wire cavity and just follow the cavity to the bridge stud?

Yes, exactly that - from the control cavity into the hole the wire now comes out of - you may have to remove the neck volume pot to get enough clearance. The size of the screw depends on the diameter of the hole, but probably about 3-4mm.

There’s a photo here somewhere, I think of a Les Paul Deluxe, where it’s been done already.

Aha, found it - https://imgbb.com/4mHXn3W

Brilliant, thanks John

It'd have taken me ages to find that! (I measured the hole, it seemed to be around 4mm diameter as you said, and the distance to the tailpiece stud seemed to be around 45mm, does that sound about right? You're quite right about the neck volume, I think I'll probably have to take it out.)

Does it need to be a solid core uninsulated wire, or does it just connect to the screw a bit more securely? (Or maybe that's just the one that was originally there, I seem to remember my Gibson SG has something similar!)

Just out of interest, should I be getting continuity between the strings and the bridge and between the strings and the tailpiece/tailpiece studs? It suddenly hit me today that I should maybe check that.

Dave_Mc · July 3

Apologies for bumping this, but I finally got around to ordering screws and attempting this and (this will be news to nobody) I got into some difficulties. (Don't worry, I didn't do any damage or anything.)

Should I be getting continuity between the tailpiece stud/bushing and the strings? Because I'm not, and that kind of concerns me, unless I'm misunderstanding what the bridge ground wire does. (Ironically enough I am getting continuity from the bass side bushing and stud to the strings, but not the treble side one which the ground wire connects to!)

(I'll not bother wasting too much time on the difficulties I got into until I figure out if the continuity thing is important, but basically the screw was a bit long to get a screwdriver to it easily inside the cavity (even a right-angled screwdriver), and I don't think I was going in quite straight so I couldn't get it in well enough. Either that or the ground wire which was still attached was in the way...

)

Thanks again for any help, it's much appreciated as always

(And apologies for being so clueless at even the most basic DIY

)

ICBM · July 4

That is very odd - if metal is touching metal there should be electrical conductivity. I don’t think those parts are likely to be lacquered effectively enough to guarantee complete isolation given the contact area…

Dave_Mc · July 5

ICBM said:

That is very odd - if metal is touching metal there should be electrical conductivity. I don’t think those parts are likely to be lacquered effectively enough to guarantee complete isolation given the contact area…

Thanks John

It's really strange. I just checked the guitar quickly with a multimeter there since it's late- I'll give it a more thorough go tomorrow and report back, but with a very quick check there I'm getting continuity between the strings (i.e. if I touch one string with one multimeter probe and a different string with the other probe I'm getting a beep). The actual tailpiece stud at the treble side is conducting when I put both probes onto it (at least at the bit at the inside where it screws into the bushing), but I'm not getting continuity if I touch one probe to the stud and the other probe to the bushing. I'm not getting any continuity when I touch both probes to the top of the tailpiece (though I'm not sure if that matters since if I remember correctly the same thing happened with my Gibson SG- presumably as long as the bit in contact with the strings conducts, that's all that matters).

I'm probably wrong but I kind of suspect that the bridge/tailpiece/studs/bushings aren't conducting well enough. As I said above, I came across a Youtube video about a Harley Benton bass with black hardware, and the plating on the hardware was preventing the bridge ground wire from working- but gold plating may well be different.

I'm actually not convinced that the grounding was ever working properly- I never checked the continuity before I swapped the pickups, I just assumed it was working as the noise level seemed normal. (Also while I certainly can't rule it out, I'd be surprised if I detached the bridge ground wire- the first couple of times I changed pickups I kept all the original electronics and was reasonably careful not to disconnect or pull/tug other wires etc..) The original pickups were covered- I changed pickups a lot as I had a bunch lying around, and I have a vague feeling when I changed to the covered Gibson pickups out of my Gibson SG the noise level was noticeably less than it was with the uncovered pickups I tried. I came across a video on Youtube (which might well be BS!) where someone had a Gibson where the bridge ground wire hadn't even been drilled for, and he said that it was ok with the original covered pickups, but as he was changing to uncovered he now needed a ground wire. Is that sensible or BS? (My Harley Benton currently has uncovered pickups, but I think I prefer the look of covered in that guitar, when I eventually decide what to go for I'll most likely be going covered.)

Thanks again

BillDL · July 5

Is there a chance that you at one time wrapped PTFE tape around the threads of the studs so they didn't wobble in the body bushings? Normally the threads would cut through PTFE tape and would still make some contact with the threads in the bushing, but sometimes not. I had this troubleshooting frustration once and I don't know how many times I de-soldered and re-soldered wires before it suddenly clicked that if was getting continuity to the body bushing through the ground wire but not to the bridge, then that was where the problem lay. I had wrapped PTFE take around both particularly wobbly studs. On that guitar I tugged the ground wire loose, soldered a largish blob of solder to the bare end and pushed it back through to the bushing with a thin dowel that stayed wedged in place. On another problematic guitar that had the bridge lowered very close to the body and was perfectly set up that way, I stacked very small washers on the bushing so that the thumbwheels wound down onto them and held them with enough pressure to guarantee electrical continuity without the washers rattling. Try temporarily wrapping tinfoil around the stud under the thumbwheel so it contacts the thumbwheel and the top of the bushing to see if that works. I suppose if there were oily or greasy deposits on the flats of the thumbwheels it might reduce conductivity as might any waxy or greasy deposit on the threads of the studs. A blast of electrical cleaning solvent would eliminate that from consideration.

Is yours the Harley Benton Custom DC in cherry red, or was it the 3-pickup antique white DC 600?

Dave_Mc · July 5

Thanks very much for the detailed reply @BillDL

First of all, it's the 3-pickup antique white (more like custard! though it does still look good, lol) one.

Going through your points:

BillDL said:

Is there a chance that you at one time wrapped PTFE tape around the threads of the studs so they didn't wobble in the body bushings? Normally the threads would cut through PTFE tape and would still make some contact with the threads in the bushing, but sometimes not. I had this troubleshooting frustration once and I don't know how many times I de-soldered and re-soldered wires before it suddenly clicked that if was getting continuity to the body bushing through the ground wire but not to the bridge, then that was where the problem lay. I had wrapped PTFE take around both particularly wobbly studs. On that guitar I tugged the ground wire loose, soldered a largish blob of solder to the bare end and pushed it back through to the bushing with a thin dowel that stayed wedged in place.

Nope, I haven't done anything to the studs. I bought it new, so I'm guessing they're not wrapped in tape, but I could be wrong! I'm working on memory here (I'm not at home at the moment to check), but I'm nearly sure I checked continuity from the end of the bridge ground wire in the electronics cavity to the tailpiece, and wasn't getting any. However, I can't remember if I checked to the bushing. I must check that tomorrow if I get a chance.

BillDL said:

On another problematic guitar that had the bridge lowered very close to the body and was perfectly set up that way, I stacked very small washers on the bushing so that the thumbwheels wound down onto them and held them with enough pressure to guarantee electrical continuity without the washers rattling. Try temporarily wrapping tinfoil around the stud under the thumbwheel so it contacts the thumbwheel and the top of the bushing to see if that works. I suppose if there were oily or greasy deposits on the flats of the thumbwheels it might reduce conductivity as might any waxy or greasy deposit on the threads of the studs. A blast of electrical cleaning solvent would eliminate that from consideration.

I'd need to check to be sure, but I think the bridge is at a pretty standard height. (In fact I suspect if anything it's high-ish, as one of the reasons I changed pickups so much was that I realised I could quickly and easily get pickups in and out just by loosening the strings!)

Presumably that would only help if the problem is at the bridge, not the tailpiece? And if the bridge is too low?

Also when you say "electrical cleaning solvent", you mean contact cleaner, don't you? (I've got some of that.

)

Having thought about it a little more, I'm assuming that if I'm getting continuity between the strings, that must mean that either the tailpiece is conducting (at least the bit the strings are attached to), or the bridge, or both. (Unless it maybe has a graphite nut, would there be enough graphite in the nut to make it conduct? I forgot to check that too!)

If that's the case (and assuming I haven't snatched defeat from the jaws of victory by killing the bridge ground wire when I tried to put the self-tapping screw in!

), and also factoring in that I'm not getting conductivity between the tailpiece bushing and the tailpiece stud, that would suggest to me that the problem is somewhere around the bushing. Maybe it's something to do with the finish, as @ICBM said. (Or unless something isn't touching that should be... seems unlikely though I can't rule it out as I did change strings before the first pickup swap.) Though to be absolutely sure about whether the studs and bushings are conducting, I'm guessing I'd need to take them out... or at least take the studs out.

Dave_Mc · July 7

Update- I think I've fixed it! This is both good news and kind of embarrassing...

I did what I should have done ages ago- I took the strings off to investigate further at the bridge/tailpiece (I actually just loosened them enough to get the tailpiece off, but my chronic laziness came in handy later). I'm not entirely sure why I didn't do it sooner- I think I'd convinced myself I'd messed something up while soldering, I should've remembered that I'm equally incompetent at restringing...

So apparently the stud at the treble side of the tailpiece wasn't completely tightened (you weren't too far off @BillDL !). (That wasn't obvious under string tension, it was only slightly loose.) When I checked with the multimeter I still wasn't getting continuity to the tailpiece, but I was getting continuity between the both the bushing and the stud and the sleeve of the instrument cable plugged into the guitar's jack socket. I started feeling a bit better at this point because I realised the problem was with the tailpiece, not the ground wire. (In fact I shone a torch into the bushing and I think I could see the ground wire in there.) When testing the tailpiece alone for continuity, I was getting it between some parts of it and not others. (The inside bit which is in contact with the studs wasn't conducting, which probably wasn't helping!)

I've got a nice Gotoh nickel-finished aluminium tailpiece that I bought for my Edwards and haven't got round to fitting yet. I tested it and the continuity was really good, basically all of it conducted apart from the bit covered with the protective film. I put it on the guitar (without strings) and was getting continuity between the jack sleeve and the tailpiece. So far so good.

Anyway, as I said, I'm lazy so I wasn't going to bother changing strings- the Gotoh tailpiece is the wrong colour, and I'm also not sure if aluminium is the way to go on that guitar since it's a bit bright already, at least on the bridge pickup as it's a little close to the bridge (I think) on account of the 24 frets and just the end of the fretboard being a bit big. So I put the original tailpiece back on and put the strings up to pitch... and the ground was working! I think having both the tailpiece stud tightened plus the tension of the strings must have been putting a part of the bridge which was conductive into contact with the stud and/or bushing, or alternatively was just making a positive enough contact so the ground signal was getting through. Either way, fingers crossed that it's sorted. Worst case scenario, I guess I could try to file a bit off the tailpiece to ensure a better electrical contact? Or else just buy a better tailpiece... but for the time being at least, hopefully it'll just keep working as it is.

Thanks again @ICBM and @BillDL ;for all your help, and sorry it was such a silly thing wrong with it that I didn't think of before you'd bothered typing all that!

BillDL · July 8

Frustrating at times, isn't it?

Several times I've had issues with wiring where it just wasn't working, but I couldn't see where the fault was. In a fit of frustration I've just snipped all the wires off and pulled all the pots out to make a fresh start, but while I've been doing that I've noticed that there was a wire wrongly soldered, or even worse not soldered to anything and hiding tucked away behind something. It's times like that when it's best to put it all down and start with fresh eyes the next day.

Dave_Mc · July 9

BillDL said:

Frustrating at times, isn't it?

Several times I've had issues with wiring where it just wasn't working, but I couldn't see where the fault was. In a fit of frustration I've just snipped all the wires off and pulled all the pots out to make a fresh start, but while I've been doing that I've noticed that there was a wire wrongly soldered, or even worse not soldered to anything and hiding tucked away behind something. It's times like that when it's best to put it all down and start with fresh eyes the next day.

Definitely! I thought I was the only one who did all that, lol.

It's a bit annoying that it took me so long to find the problem, but at the same time, being philosophical about it, it's better that it was a very minor problem than something which was much more difficult to fix!

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Think the bridge ground wire has disconnected on my Harley Benton SG Custom

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