Where to start eliminating variables with P pickup troubleshooting

Dynomuttasaurus

Dynomuttasaurus

Jul 23, 2016
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Milwaukee
#1
I posted a week or so ago about my weak pickups in a new entry level bass. I've never modified/customized a bass, but it seems like a lot of you had, and I wanted to give it a try on this sweet bodied-poorly electronics beauty.

I bought a soldering kit, Seymour Duncan SPB-4 and SJB-2, watched a couple videos, and sat down last night to give it my best.

Pickups came out easy.

Putting the new pickups in was more challenging, especially the P. I got the E/A split in okay, but the sticky on the foam was not sticky and I had my hands full trying to hold two layers of foam (body route was deep and required extra foam), guide wires and cram the D/G split in all at the same time. I thought I had it all in good and started to screwed in the mounts.

Turned it over to connect the wires and the black wire had disappeared.

I removed the D/G split and found that I had somehow sent the mounting screw right through the middle of the black wire - and then twisting the wire around the screw. I undid my mess and looked at the wire. The screw had gone through it, but hadn't severed it.

More carefully, I remounted the split. Installed the J easily. Soldered the wires. Restrung. Gave my work its first test.

Sounded sweet! Everything was working.

So I grab a multimeter and decide to see what the output is through the cable. First the P = 115k! Well, that can't be right. Check the J = 15.1k. Considering it's a hot pickup and the pots are in the equation, that seems reasonable.

So I plug in again to listen. And, I get nothing from the P. The J sounds great, possibly my best sounding J bridge of the collection.

Okay, so where to start with the troubleshooting?

1) Cut and splice the black P wire I impaled?
2) Unsolder the pickups and resolder the P to the J pot to see what happens?
3) Find someone who has actually done this sort of thing and show them what this novice has done to his bass?
4) Get a plate of carrots?
 
#2
I can't rule out damage to the wire after it is impaled. Try the pickup directly to the jack, and then replace the wire. Was there any other damage to the pickup?
 
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#3
First off, props for getting and using a meter. :thumbsup: The 115K ohms sounds like the two volume pots in parallel with each other. Measuring resistance at the jack can be useful, but it's important to remember the pots are (should be) in parallel with the volume pots. You can't measure a pickups' resistance directly once it's connected to a volume pot. (It's resistance can be calculated if the resistance of the pot is known)

Secondly, there's some 'easy' stuff to check for: make sure none of the bare pot terminals or jack terminals are contacting the sides of the controls cavity. Sometimes a volume pot will work loose, rotate a bit, and a terminal will ground out on the sheilding. You didn't mention what wiring scheme you're using, I suppose it's the standard volume, volume, master tone, like a Jazz bass?

Pictures might help here.
 
#4
Crater said:
First off, props for getting and using a meter. :thumbsup: The 115K ohms sounds like the two volume pots in parallel with each other. Measuring resistance at the jack can be useful, but it's important to remember the pots are (should be) in parallel with the volume pots. You can't measure a pickups' resistance directly once it's connected to a volume pot. (It's resistance can be calculated if the resistance of the pot is known)

Secondly, there's some 'easy' stuff to check for: make sure none of the bare pot terminals or jack terminals are contacting the sides of the controls cavity. Sometimes a volume pot will work loose, rotate a bit, and a terminal will ground out on the sheilding. You didn't mention what wiring scheme you're using, I suppose it's the standard volume, volume, master tone, like a Jazz bass?

Pictures might help here.
Click to expand...

Yes, it is a volume/volume/tone setup. It's an unshielded control cavity (maybe I should add that to-do while messing around with the rest of the electronics). Below is a reference picture I took last night. Sorry about the blurriness. I spent $1 on my phone and got what I paid for.
28059289_10156051948702980_8281657743420834139_n.jpg
 
#5
Measuring DC Resistance with the pickup installed won't work. You'd need to disconnect at least one wire of the pickup, because the pots are in parallel with the pickups & mess up your reading.
I'd try wiring the P pickup directly to the jack, just to be sure it's not the pickup. Isolating components is key in troubleshooting.
 
#6
Yes, unsolder the pickup from the rest of the electronics, test it, and then wire it to the jack to at least isolate the pickup being the problem.
 
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#7
Zoobiedood said:
Yes, unsolder the pickup from the rest of the electronics, test it, and then wire it to the jack to at least isolate the pickup being the problem.
Click to expand...
I had a little time today, so I did the above. I unsoldered the P pickup and wired it to the Jack direct. Boom! I've got volume and a 13.0k reading on the meter. Connect it back up to the pot ... Nothing. Change pot with another 250 K scavenged from a defunct guitar ... Nothing. The J pickup still works perfectly.
 
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