Humbucker problem in 1970s Yamaha SG 2000

[sgelectric]

Hi, This my first post in the pickup forum.I am a total novice when it comes to PU troubleshooting.
I have a problem with the neck PU on my SG 2000.
At first I thought I had a selector switch problem but that now appears not to be the case.
I loosened the strings,removed the mounting screws and flipped the PU over. It reads in excess of 300k ohms at the contacts on the back plate.The bridge PU reads out at 6.6K ohms through the switch and harness.

What are the common failure modalities in humbuckers? I have not yet removed the cover to inspect coil connections etc.....

Any insights or suggestions would be greatly appreciated.I'm hoping it may be possible to repair the PU.

Thanks, Steven

[Peter Naglitsch]

I would start with the connections. Check the soldering. If they look suspicious, reflow them with medium heat and check again.

[sgelectric]

Peter, Thanks for your reply.
I will reflow the connections when I get a chance and report back.
What would you define as "medium heat"? I use 650F on Fender PCBs but hotter on eyelets, turrets, point-to-point etc............
Steven

[big_teee]

To test a pickup on a SG guitar I would do it from the control cavity on the rear of the guitar.
Take the cover off the back and check each pickup there, if necessary unsolder the wires from the pot.
If they read high at the pickup wire, or open, then you have a bad pickup.
If they read normal, then you have a switch, jack or pot problem.
If everything is working correctly you can check the guitar with a cord plugged into the guitar with no amp.
Turn the volume pots on high and read each pickup thru the guitar cord.
The pickups will read a little lower in ohms that way wired to the guitar.
T

[dwmorrin]

What are the common failure modalities in humbuckers?

Most common failures: open wire, or shorted wire. At the end of the day, it's just a long piece of wire and magnets. If your reading the dc resistance, that is only taking the wire's resistance into account. 300k is probably a pot reading, and the pickup may be open.

In your case, something is open. If you're lucky, its a solder connection, but often it is not. Be careful if you take the cover off.
Is it repairable? Yes. But the repair may require unwinding the coil, finding the break, and rewinding it.

[David King]

I have no idea how these pickups were wired up once wound but if it has eyelets or terminals on the back plates then definitely reflow those joints as that's the most likely source of a high resistance reading (on a pickup that has been disconnected from the harness).
If a coil is open then don't spend a lot of time figuring out where. If there are taped, wire to wire connections inside the cover you can reflow those or look for an obvious break at the surface. Otherwise just slice all the old wire off with a sharp chisel and rewind it. Or send it out to your local rewind shop as is so they can determine what wire was used and guesstimate on the number of turns. I'll bet there are several dozen shops in LA that can do this for you for $30-50. Or you can buy a cheap Asian GFS or equivalent pickup for not much more and it might even sound better.
Or buy a really good domestic pickup and get a great sounding guitar in the bargain.

[sgelectric]

Thanks for all the responses.
I have a friend who winds pickups so I'll take it to him and let you know how things sort out.

Again, Thank you all.
SG

[David King]

SG,
Feel encouraged to post detailed photos of these pickups here for future reference. Perhaps your winder friend could do the same for the insides. That will undoubtedly help someone else in the future.

[big_teee]

I agree with DK, I wouldn't spend much money on a repair.
Either rewind it or replace it, if the coils are open.
T