How do I diagnose a "broken" active pickup?

[LeftyJ]

Last week I acquired a German-made 2001 Warwick Streamer LX for a great price. It has the stock MEC PJ active pickups and 2-band electronics with push-pull volume for EQ bypass and a balance pot. The pickups are sealed with black epoxy and the insides can't be reached without breaking the cover or the epoxy seal. The pickups are 3-conductor: a hot, a combined ground/- for the 9V power, and the + for the 9V power. The wiring disappears straight into the epoxy. 

The splitcoil does not produce any signal whatsoever. I have tried isolating it and using a multimeter to measure it, but I'm a little lost. With regular passive pickups, I can just unsolder them and measure on the hot and the ground and I'll roughly know what kind of resistance to expect and what to look for. The MEC pickups constantly require 9V though, and are very low-impedance. The bridge pickup appears to give 1.1kOhm with the 9V connected (and goes all over the place with the battery detached), the neck pickup none. It appears the signal is interrupted somewhere, but I can't find the source.

What do I look for, and what possible problems could there be? I really don't know where to look. Thanks!

Edited January 14, 2021 by LeftyJ

[BigRedX]

There isn't any way to do this.

These "active" pickups are just a standard coil around a magnet (albeit at a different impedance to "passive" pickups) wired directly to a pre-amp/impedance matching circuitry all encased in epoxy.

What you are actually measuring is the impedance of the output side of the "active" electronics and gives no indication of what the coils are doing. In fact the problem is far more likely to be a failure of one of the pre-amp components, rather than a problem with the coils.

I think if it really is dead you'll probably have to bin and replace.

[itu]

Signal chain of a bass:

pickups - blend - vol - tone set - output

Any cables that are not connected?

If you have a DMM, measure the output of the pickup. If it works, fine. Then check the pots, one by one. It is not the first time when a pot is defective.

A suitable blend pot replacement would be a Bourns 250 k MN.

[LeftyJ]

250k would definitely not be suitible for low-impedance pickups. The stock MEC blend pot is 25k.

As you can read in my first post, I already measured with a digital multimeter. The pots are fine, and all the wiring is connected and looks fine. I have already isolated the culprit, I know it's the neck pickup. I'm just hoping to find out what's wrong with it, and if it's fixable. 

Thanks @BigRedX, I feared as much 🙁

[itu]

Can you measure the pickup from the pickup end, or are the wires also in the epoxy? If so, in this case of a dead end you could cut the insulator from side a bit and measure conductivity to the pots and if there is any signal or voltage there. If the signal is found, the cuts can be fixed with some shrink tube.

[LeftyJ]

The cables go straight into the epoxy. The signal wire is a hot (core) with the ground as a sleeve around it, so I can't reach the core wire closer to the pickup. The red wire is the 9V +. 

I ordered a new one today through the Warwick webshop. 

[LeftyJ]

New pickup arrived today, I installed it this evening and it sounds great. The bass is in perfect working order again. Thanks!