Epiphone LP bridge pick up problem

[David Shore]

I have a Epiphone LP that is not getting any sound from the bridge pick up. Here is a list of things I checked/done:

- Check continuity in the circuit. Everything checked out.

- Tested the resistance of the pick up. Fine.

- Replaced the 3-way switch.

- Tested the pot. It's working fine.

 

Though I'm not getting sound from the pick up, I do hear a slight "hiss" when the volume pot is turned between 3 and 8. No sound at all when on 0 and 10 which would seem like there's a grounding issue but I just can't seemed to locate it. HELP!! 

 

Thanks for your help in advance everyone! First time poster..be easy on me! haha

[David Shore]

Thanks for all the help everyone! It was the p/u after all. Rob, I appreciate all the advise and I will use it for future electronic failures that I know will come my way! :)  Take care.

[Rob Mercure]

Hey advise is about all I'm good for these days - am semi disabled and looking forward to a liver transplant sometime this autumn if one comes available.  So I really can't lift much and it's frustrating knowing how many of my own projects I can't currently fix - so helping others is a relief so thanks to you.

 

Now something's absolutely strange about your readings and I wonder how old/in calibration/good your meter is.  Hooking up the pickup directly is a definitive test but assuming you've got a humbucking P/U you should be reading somewhere around 4-5,000 ohms minimum - even the low impedance P/Us on the old Les Paul "Recording" guitars of the early 1970s (which needed a matching transformer to drive an amp directly) read a bit over 100 ohms DC.  In fact, if you're reading is correct I don't see how you can get a signal from either P/U as the resistance/impedance is so low that well over 95% of the signal would be shorted out.  Go to Rat Shack if you have to and buy a couple of 1% tolerance resistors - say 10, 1,000. and 100,000 ohms and note how close your meter reading is to the designated resistor value.  You really don't know how often over the years a malfunctioning piece of test equipment has wasted huge amounts of my time.  Anyway with the P/U connected directly to the jack then solder in the volume control - each P/U lead goes to an outside lug of the pot - facing the back of  the pot the lug on the left is ground so just attach it without breaking the connection while the other pickup lead goes to the right hand lug and the signal to the jack goes to the jack, then test the volume control.  Next the cap lead attaches to that came center lug while the pot the cap is attached to outside lug attaches to ground - if that works then all you've got left is the switch.  Now while Gibson switches have been known to last for years they're actually a variation of the old time switches used by telephone exchanges back when there were banks of telephone operators.  Being open they're very subject to corrosion, bent contacts, and general poor connections - here's where you need a good ohmmeter that will read low resistances well (Fender switches are also open but a little better protected - unfortunately they don't have as much "bounce back" if hit hard so probably more Fender switches fail even though it's a slightly better design - but I don't think that anyone that I know of makes a sealed aftermarket switch that will take either the Gibson screw on knob or the push on Fender type).  So, when you get back to it I guess we'll find out but do yourself a favor and buy a good DMM if you don't have one already as this is a "lifetime" tool that will help you with car work and house wiring and simple but important stuff like making sure that a circuit isn't energized before you put your hand in.  There used to be scores of US manufactures, Simpson, Triplett, RCA, GE, and the ubiquitous EICO and Heathkit but the only one I can currently recommend (no pun intended) if a Fluke.  I new one will set you back at least $70 but I've seen them on e-beast go for lots less and picked up my spare for $20 at a flea market (I always take a meter to flea markets to test before I buy).  If you've got an old neighborhood TV repair shop that's struggling with some old guy just keeping it going or if you know any professional electricians ask them - you should be able to get a good used Fluke for less than the full retail cost of a couple of sets of Elixer strings <grin>.

Rob

[David Shore]

I am currently using the Fieldpiece MM I got through Stew-Mac a year ago. It works great..I'm just not so sure the user is worthy :)

 

I think I made a mistake in telling you my reading on the p/u was 14.38 ohms. What I meant to say was 14.38K ohms. That's more like it, but obviously something was still not adding up. I desoldered the neck p/u and took a reading and got 8.34k ohms. That is more typical reading from that particular p/u. Something is shorting out in the bridge p/u.

 

Do you have any ideas of what would make the bridge p/u read twice the normal resistance? I'm clueless! Thanks.

[Rob Mercure]

When you unsoldered the P/U the volume pot was still in circuit so you were seeing the resistance between the wiper of the pot and the ground - obviously it was turned up just a wee bit as it's a 500K pot.  With the P/U still disconnected turn the pot up like you wanted the P/U to be as loud as possible and you should read somewhere around 500 K ohms (a couple of thousand low doesn't hurt).  Now turn the pot down all the way and you should read close to zero - no more than 50 max.

The problem is that we're mixing electronic terminology for simplicity.  The number usually associated with a P/U is "impedance" which is a vector function of inductive reactance and ohms - and since the reactance changes with frequency the impedance number is only "accurate" at one frequency (same with a speaker also).  What you're measuring is DCR - resistance to direct current - and it's always fraction of the impedance, often about 4/5 or so (but this depends on so many things that that "guesstimate" can easily be wrong - for speaker's it's usually about right).  So I'm not sure what DCR you read from you sentence (an really tired right now) but the 8.34 seems about right and the 14.38 seems a tad high but some really high output P/U can easily have enough wire to read that high - humbuckers have two coils in parallel and when you put resistance in parallel it drops while it adds in series.  This is why single coils read higher but a coil tap on a humbucker can bring it up as high as a single coil.  So the P/U is "ballpark" - but now you need to figure out if the volume pot is working right.

Later - gotta take a bath and crash out.

Rob