Troubleshooting EMG's

[bagman67]

So I recently came into possession of a handful of beat-to-hell (or at least poorly-maintained) electric guitars.  They were left out of their cases for years in a home not far from the mighty Pacific ocean, so there's crud and chrome-pitting and so on.  Lots to clean up, and they'll never be worth the cost of replacing the brightwork.  I am very excited to use them to refine my guitar-tech skills and then probably donate them to the local Boys & Girls Club. 


Anyway:  Among the hoard is one reasonably valuable axe, an LTD MH-1000 Deluxe, equipped with EMG humbuckers (an 85 in the neck and an 81 in the bridge, per the factory specs).  When I plug the guitar in and roll the volume to wide open, i get very, very weak output and more noise than I would expect with the active humbuckers.  The volume does go to zero when I roll it off all the way.  Tone pot seems to be functioning correctly.  I have replaced the battery with a fresh Duracell and verified the old one did not burst or ooze crud in the cavity.  So - next step is to start testing other things. 


My question, finally, is:  Does this sound like a worn-out volume potentiometer?  Or does anything else come to mind?

 

[rgand]

Wow, nice grab. I've never messed with active pickups. Is it possible that the pole pieces have been magnetized somehow and cancel out the working of the pickup? I say that because I accidentally de-magnetized a pickup in a guitar with a fairly sizeable magnet. Careless, but it can happen.

 

[Cagey]

Pot failures range from intermittent opens (scratchy), increased resistance, fully open, or mechanically broken. In almost all cases, the symptom is going to be increased volume of some sort, so I wouldn't suspect a bad pot.

Active pickups usually have some sort of internal preamp, which I can see having a variety of failure modes, so outside of a wiring issue I'd be blaming that pretty fast.

 

[spe111]

I definitely agree with the preamp. I'd start by making sure that the voltage on the battery is getting where it's supposed to go on the printed circuit board.

 

[mayfly]

I'd check that power is making it's way onto the preamp.  After that was confirmed, I'd check the connections between pickups and preamp.  Then I'd do a signal trace through the entire system to find the bad point.

 

[TonyFlyingSquirrel]

I've worked on plenty of EMG equipped guitars, and never once have I come across a dead pickup, either coil wise or pre-amp wise, but I have come across plenty of bad wire jobs that I've had to correct/clean up.  I do work for a local music store franchise and 90 % of the jobs they give me are wiring related, and I've had at least 6 that were bad wiring jobs from the factory, including a $1500 Fender Performer Series Strat that had multiple cold soldier joints on it.  They couldn't put that on the rack until it got corrected.

EMG's are now dirt simple to wire up, and it doesn't take an experienced tech on average to install their soldier-less system.