Precision bass '71 very low signal

[JJJack]

I got a '71 Precision bass last year (a trade on BC) and all was well. I picked it up the other day, plugged in and got no sound. I had to turn the amp up high before I could hear it.

Up until that point there was no issue with the signal.

What are the most sensible first tests to fault find? E.g.

If I measure the resistance of the pickup whilst it's solder to pots etc. What sort of reading would I expect?

Suggestions please.

Jack

[JJJack]

More information.
Resistance across the left hand pickup was 5.6k
Resistance across the right hand pickup was 256k

Not good?

Jack

[MoonBassAlpha]

[quote name='JJJack' timestamp='1468610202' post='3092186']
More information.
Resistance across the left hand pickup was 5.6k
Resistance across the right hand pickup was 256k

Not good?

Jack
[/quote]
Sounds like a visit to the pickup hospital is required.

[JJJack]

Can you suggest any reputable pickup hospitals?
Jack

[Twincam]

You should measure the resistance with them disconnected!

[Twincam]

And too add to what I said that's the same when testing pots.
If you measure when things are connected its going to effect the reading.
So your measurements are not accurate there.

[JJJack]

Fair comment twincam. But the huge difference in resistance between one pickup and the other is not right though is it?
One thing that concerns me greatly is that I got the bass for its original condition and I want to avoid affecting it's "purity". Mind you, if it doesn't work it needs fixing!
Jack

[Beer of the Bass]

[quote name='Twincam' timestamp='1468691090' post='3092723']
And too add to what I said that's the same when testing pots.
If you measure when things are connected its going to effect the reading.
So your measurements are not accurate there.
[/quote]

Components in parallel will reduce the resistance reading across the pickup, but never increase it. So while measuring a pickup coil in circuit will under-read slightly, a 256k reading almost certainly indicates an open coil. I suspect the meter will be seeing the 250k resistance of the pot, and the coil would measure open if tested out of circuit.
Depending where the break is, it may be possible for the repairer to just unwind a couple of turns and re-solder rather than doing a full re-wind.

[luckydog]

If you're lucky, the high resistance will be at the junction between one of the PU lead connections and the ultrafine wire that forms the coil. That fine wire is so delicate it normally either conducts or it breaks completely, so a high resistance suggests the solder connection inside the PU if you're lucky. HOWEVER, repair requires the finest of soldering skills, and isn't a DIY job unless you have the eyesight of a hawk and super steady hand plus highly skilled soldering.

Then it's best to follow advice and send it to a quality repairer, one that aims to preserve as much of the original as possible.

I successfully DIY repaired a '74 Jazz pickup this way, but not for the fainthearted !

LD

[JJJack]

Thanks all.
I will check out the mojo blog man.
Cheers
Jack

[Twincam]

[quote name='Beer of the Bass' timestamp='1468707095' post='3092855']


Components in parallel will reduce the resistance reading across the pickup, but never increase it. So while measuring a pickup coil in circuit will under-read slightly, a 256k reading almost certainly indicates an open coil. I suspect the meter will be seeing the 250k resistance of the pot, and the coil would measure open if tested out of circuit.
Depending where the break is, it may be possible for the repairer to just unwind a couple of turns and re-solder rather than doing a full re-wind.
[/quote]

Good point! And likely correct.
But I would still of tested unsoldered. And any pots etc unsoldered just to double check before sending anything off.

[rmorris]

[quote name='Beer of the Bass' timestamp='1468707095' post='3092855']
Components in parallel will reduce the resistance reading across the pickup, but never increase it. So while measuring a pickup coil in circuit will under-read slightly, a 256k reading almost certainly indicates an open coil. I suspect the meter will be seeing the 250k resistance of the pot, and the coil would measure open if tested out of circuit.
Depending where the break is, it may be possible for the repairer to just unwind a couple of turns and re-solder rather than doing a full re-wind.
[/quote]

+1 the lower resistance measurement is reasonable. The 256K reading indicates a basically open circuit pickup with the reading being basically the attached pots. Anyway it's the problem. Confirm by removing pickup and measure in isolation.

Edited July 26, 2016 by rmorris