Pickup dead and need help 74 Greco JB450

[drumfunky]

Hi all, a pickup screw broke at the bottom of the pickup cavity. When I replaced the screw suddenly the pickup died.
A little background, I couldn't get the original screw out. It's flush with the bottom and my extractor didn't work. I put
the new screw in at a slight angle next to the old one. I did open up the electronics plate so I could get the pick out a bit more.
What should I check first??? I don't see contact spots on the bottom of the pickup to check the ohms like on a guitar pickup.
The bridge pickup measures 6k but the neck pickup measures 114K. Could it be a bad pot and how do I measure that??
I'm lost on what to do. I'm a career drummer that recently
switched to bass after a neurological problem. Thanks so much for the help

 

[LoveThatBass]

Depends where you are reading. Are you reading at the pickup, at the pot or from the output Jack. All but the pickup it could be the pot, however I suspect something happened to the pickup while you were messing with the screw.

 

[drumfunky]

Depends where you are reading. Are you reading at the pickup, at the pot or from the output Jack. All but the pickup it could be the pot, however I suspect something happened to the pickup while you were messing with the screw.

I was measuring from the jack. I'm not sure how to measure from the pickup itself. Thanks

 

[definenredefine]

The bummer part of this is those old Maxon pickups are kinda hard to find, and they're usually like $100 if you do find them. The upside is that allparts makes a similar (at least similar looking) pickup - PU-0419-010 Bass Humbucking Pickup Bridge

 

[newfuture]

Best to test at the leads coming off the pickup if there are no visible solder points on the pickup itself.
Not knowing the schematic, you might lift and probe each hot lead from the pickups separately. Depending on the schematic, this might not be necessary.

 

[drumfunky]

Best to test at the leads coming off the pickup if there are no visible solder points on the pickup itself.
Not knowing the schematic, you might lift and probe each hot lead from the pickups separately. Depending on the schematic, this might not be necessary.

Appreciate that so much

 

[drumfunky]

How do I tell if my pot is dead?

 

[newfuture]

It's probably fine, but this is how I check pot operation-

Measure resistance across the outside lugs. This should match the printed resistance +/-20% (often)

Now measure one outside lug to the center lug (this is the wiper). With the knob all the way to one side will be zero ohms, all the way to the other side should be the printed value. Then measure the other outside lug to the wiper and do the same test. Zero and printed value will be opposite the first test. As you sweep, the value will change in either a linear or logarithmic fashion and have no giant jumps to infinite resistance or zero.

If you can post a pic of the controls and wiring that might be helpful

 

[drumfunky]

It's probably fine, but this is how I check pot operation-

Measure resistance across the outside lugs. This should match the printed resistance +/-20% (often)

Now measure one outside lug to the center lug (this is the wiper). With the knob all the way to one side will be zero ohms, all the way to the other side should be the printed value. Then measure the other outside lug to the wiper and do the same test. Zero and printed value will be opposite the first test. As you sweep, the value will change in either a linear or logarithmic fashion and have no giant jumps to infinite resistance or zero.

If you can post a pic of the controls and wiring that might be helpful

Aw Bud, thanks so much. Will post a picture tomorrow and take your advice.

 

[drumfunky]

It's probably fine, but this is how I check pot operation-

Measure resistance across the outside lugs. This should match the printed resistance +/-20% (often)

Now measure one outside lug to the center lug (this is the wiper). With the knob all the way to one side will be zero ohms, all the way to the other side should be the printed value. Then measure the other outside lug to the wiper and do the same test. Zero and printed value will be opposite the first test. As you sweep, the value will change in either a linear or logarithmic fashion and have no giant jumps to infinite resistance or zero.

If you can post a pic of the controls and wiring that might be helpful

 

[Killing Floor]

Possible a coil wire was broken?

 

[drumfunky]

I cut the pickup wire and measured reading 1k. So that probably is a bad coil wire right? Do I need to buy matching pickups or can replace with something else? What's a good pickup for this bass? Thanks all.

 

[newfuture]

1k is a weird reading, I would expect either infinite resistance (coil totally open) or zero ohms (dead short). A short mid-coil can happen, but I don't think I've seen it personally. If you had one, I would expect a little, very weak, output.

That said, if the reading is wildly different from the other pickup that works, you may well have a dead PU.

As for replacement recommendations, can you post a pic of the bass front? I'm sure more knowledgeable folks will chime in.

 

[drumfunky]

1k is a weird reading, I would expect either infinite resistance (coil totally open) or zero ohms (dead short). A short mid-coil can happen, but I don't think I've seen it personally. If you had one, I would expect a little, very weak, output.

That said, if the reading is wildly different from the other pickup that works, you may well have a dead PU.

As for replacement recommendations, can you post a pic of the bass front? I'm sure more knowledgeable folks will chime in.

Thanks for the help.
1974 Greco jb450

 

[definenredefine]

I could be wrong but I think any standard Jazz bass sized pickups should work. If I'm right, there are many, many options available to you.

 

[drumfunky]

would a

Fender '62 Vintage Jazz Bass Neck Pickup work???​

 

[definenredefine]

would a

Fender '62 Vintage Jazz Bass Neck Pickup work???​

Check the measurements, but quite possibly!

 

[drumfunky]

Check the measurements, but quite possibly!

Put in the pickup and it sounds great! I have 2 of these jb450s. One might be for sale soon.

 

[definenredefine]

Put in the pickup and it sounds great! I have 2 of these jb450s. One might be for sale soon.

Awesome! Glad it worked out for you!