P-90 now has 1/2 output

[marmatkat]

Hi Folks. I'm new to the forum and I have a question. I have a '93 Hamer Special that (I was told) has Loller "Wind" pickups (I haven't verified this). The guitar has worked great for the four months I've had it, and yesterday while asking a local tech about some fret buzz, he ave me advice about the pickups being slightly loose in their cavities. He said to tighten down the two screws until they are snug to the bottom. Not thinking about it, I tried that at home but realized (belatedly) that those screws adjust the pickup height. After tightening the neck pickup down, I raised it back up and found that it now has ~1/2 the output. A friend said I probably broke it :-(

I'd appreciate your thoughts on a) what might have happened, b) how I can verify this (e.g., by measuring the resistance), and c) if it's toast, what replacement you might recommend. (I play in a cover band, ranging in style - rock, country, jazz, pop, etc.) Thanks in advance from an embarrassed newbie.

[A little more detail: The neck is about 1/2 the output of the bridge. The middle pickup setting (3-position switch) no longer has the humbucking sparkle. Now it sounds exactly like the bridge. With just the neck pup selected, the output goes to zero when I turn the tone knob all the way down.]

 

[gregory]

Re: P-90 now has 1/2 output

Have you tried adjusting the height since you unwittingly futzed with it the first time around?

 

[freefrog]

Re: P-90 now has 1/2 output

Now it sounds exactly like the bridge. With just the neck pup selected, the output goes to zero when I turn the tone knob all the way down.

These two symptoms suggest a broken wire whose ends are still close to each others and behave like a capacitor... The same problems would be noticed if the pickup was intact and soldered with a capacitor in series.

If it's the case, an average multimeter should measure no DCR but a capacitance of a few nanofarads (with an intact pickup, it's the contrary: the DCR can be read and any capacitance reading fails).

Maybe the pressure on the bobbin has squashed the coil and broken it.

Now, it could also be the coaxial cable going from the pickup to the controls: if the pickup has squashed it, it might have cut one of the two conductors inside the coax cable, changing this bi-conductor in an unwanted capacitor.

Pull off the strings, pull off the pickup, check its coax cable. If it's damaged, it's not hard to repair or replace.

If the coil is damaged, it's possible to repair it as long as the broken wire is on the outside section of the coil. If it's an inner cut, the coil will have to be rewound.

FOOTNOTE - I've already repaired several pickups with such issues... but according to some , several famous tunes have been recorded with pickup featuring capacitive broken wires (!)

Good luck...

 

[marmatkat]

Re: P-90 now has 1/2 output

> Have you tried adjusting the height since you unwittingly futzed with it the first time around?

Yes, and no joy. Thanks, though.

> If it's the case, an average multimeter should measure no DCR but a capacitance of a few nanofarads (with an intact pickup, it's the contrary: the DCR can be read and any capacitance reading fails).

Do I need to de-solder the pickup before measuring? Or can I select just that pickup by itself using the switch?

> Pull off the strings, pull off the pickup, check its coax cable. If it's damaged, it's not hard to repair or replace. If the coil is damaged, it's possible to repair it as long as the broken wire is on the outside section of the coil. If it's an inner cut, the coil will have to be rewound.

That's really helpful - thank you. I'll have a look. Owning a $econd guitar would be handy right about now.

 

[freefrog]

Re: P-90 now has 1/2 output

> If it's the case, an average multimeter should measure no DCR but a capacitance of a few nanofarads (with an intact pickup, it's the contrary: the DCR can be read and any capacitance reading fails).

Do I need to de-solder the pickup before measuring? Or can I select just that pickup by itself using the switch?

You can select just the pickup and measure its DCR through the output jack.

Good luck again. I hope you'll solve your problem.

 

[marmatkat]

Re: P-90 now has 1/2 output

Much obliged. I need to research how to get the pickup out without buggering it further. I assume just raise it using the two screws, but I'll verify before trying it.

 

[freefrog]

Re: P-90 now has 1/2 output

Watch the post 5 in this thread: http://www.tdpri.com/threads/p90-neck-install.574177/

In a Hamer, you should find the same kind of foam under the pickups (unless the previous owner did put springs around the height setting screws). With such a simple mounting disposal, P90's are usually easy to pull off and to reinstall.

 

[marmatkat]

Re: P-90 now has 1/2 output

Watch the post 5 in this thread: http://www.tdpri.com/threads/p90-neck-install.574177/In a Hamer, you should find the same kind of foam under the pickups (unless the previous owner did put springs around the height setting screws). With such a simple mounting disposal, P90's are usually easy to pull off and to reinstall.

Much obliged. I'll follow up after I remove it (carefully!)

 

[GuitarDoc]

Re: P-90 now has 1/2 output

The advice you got to tighten down your pups was for dog-eared P-90s. What tech would tell you to do that with soapbars? Did he actually look at your guitar before giving you that advice?

[A little more detail: The neck is about 1/2 the output of the bridge. The middle pickup setting (3-position switch) no longer has the humbucking sparkle. Now it sounds exactly like the bridge.

Are these stacked humbucking P-90s? Sounds like a broken wire. But...

With just the neck pup selected, the output goes to zero when I turn the tone knob all the way down.]

This is confusing. Are you sure all you did was adjust the pup height? Did you do anything in the control cavity? A broken pup wire won't make your tone pot function as a vol pot.

 

[freefrog]

Re: P-90 now has 1/2 output

A broken pup wire won't make your tone pot function as a vol pot.

When the ends of a broken wire stay directly close to each others, they accidentally form a capacitor and the pickup behaves as if it was in series with a cap. IOW, it appears to include a high pass filter. The tone pot still works like a low pass filter. The conjunction of these two parameters makes the tone pot function as a volume control.

It's a relatively common issue, easy to detect with a lab DMM and a frequency analyzer. The last pickup that I've repaired with such a problem was a Duncan Custom, a few months ago.

 

[marmatkat]

Re: P-90 now has 1/2 output

(For anyone new to this post, I'm debugging a problem where I tightened down my Hamer's neck P-90 per bad advice and then found the pickup output was now ~1/2 of the bridge one. Additionally, the middle pickup setting on the 3-position switch no longer had the humbucking sparkle, and instead sounded exactly like the bridge. And with just the neck pup selected, the output went to zero when I turned the tone knob all the way down.)

OK, please see if you can make sense of this. It is now working correctly, but I can't pinpoint why. Here's I did (pics below):

• Lifted the neck pickup out of its cavity, but did not open up the control cavity.
• Inspected it and wires for damage. The braided wire did not have any obvious damage. Of the two solder connections on the corners, one had the two wires next to each other, but the other pair seemed to be flattened and separated. I used my fingernail to very gently push them together, given the above comments about capacitance.
• Remounted the pickup and tried it in an amp -> still broken.
• Opened the control cavity and poked around the solder joints and wires a bit. Nothing looked odd or seemed loose. Tried to measure resistance across different points, but really didn't know what I was doing, so put the cover back on. Tried it through the amp, and found it worked fine! WTF?
• Measured resistance of each pickup at the output jack: Neck: 6.79k, Bridge: 7.08k. The specs say they should be 7.1K and 7.4K respectively. Why are they lower? That means lower output, right?

At this point, until I understand what happened, I'm nervous about another failure. Thanks again for your attention!

 

[GuitarDoc]

Re: P-90 now has 1/2 output

From what you just said you did, it sounds like there is a bad solder joint or broken wire somewhere. Even tough the solder joints may all look and feel good, somewhere at least one is not making good and consistent electrical connection, or like I said it could be a bad wire.

 

[freefrog]

Re: P-90 now has 1/2 output

(OK, please see if you can make sense of this. It is now working correctly, but I can't pinpoint why. Here's I did (pics below):

• Lifted the neck pickup out of its cavity, but did not open up the control cavity.
• Inspected it and wires for damage. The braided wire did not have any obvious damage. Of the two solder connections on the corners, one had the two wires next to each other, but the other pair seemed to be flattened and separated. I used my fingernail to very gently push them together, given the above comments about capacitance.
• Remounted the pickup and tried it in an amp -> still broken.
• Opened the control cavity and poked around the solder joints and wires a bit. Nothing looked odd or seemed loose. Tried to measure resistance across different points, but really didn't know what I was doing, so put the cover back on. Tried it through the amp, and found it worked fine! WTF?
• Measured resistance of each pickup at the output jack: Neck: 6.79k, Bridge: 7.08k. The specs say they should be 7.1K and 7.4K respectively. Why are they lower? That means lower output, right?

My 2 cents again, FWIW.


The "flattened" wires are a possible cause of the "capacitive" behavior that I evoked. [EDIT: if it was me, I would redo the related solders or would simply melt them once in order to "fasten" anything loose... but if it ain't broke, don't fix it.]

The resistance that you measure is normal: when pickups are in a guitar, their DCR is lowered by the DCR of the pots. There's a formula to calculate it: 1/ [DCR or the pickup] + 1/ [DCR of pot A] + 1/[DCR of pot B] and so on.

Then calculate 1/ the result obtained and you have your "final" DCR.

Example with a neck PU measuring 7.1k by itself + a 300k vol pot + a 300k tone pot: 1/7.1 + 1/300+ 1/300 = 0.147. Then 1/ 0.147 = roughly 6.8k when the pickup is in the guitar. How surprising! )

Your pickup works again once you put it back: it can be explained too. For example the simple pressure of the foam might push on a defective contact and "secure" it when the pickup is mounted in the guitar.

More later about that, maybe...


The most important is that your pickup works again: don't touch it no more, cross your fingers and enjoy your guitar [but of course, you can bring it to a guitar tech too, if you want to exorcize definitively any risk].

 

[marmatkat]

Re: P-90 now has 1/2 output

FYI Here's the email I got from Jason Lollar :

[his initial reply]

Hi- the ohms read lower because they are wired into a guitar and the ohms vary anyway and air temperature also makes a difference in the reading as can your meter and how you measure

As far as the stray wire- you mean where it goes around the edge?
They could be broken off there and make no difference- the wires are looped around the edge just to tie them to the eyelet before soldering. Solder joints on the pickup look perfect.

I don’t see anything obvious in the control cavity but you cant see every solder joint- one thing that happens when the control cavity has grounding paint in it if any of your wires touch that or solder points youll ground out or if you have a stray wire that’s pulled away from the strands you can have odd things happen.

I would reinstall it- tap on the pickup from different angles and if it keeps working it was probably a fluke that we will never figure out


[his follow up reply]

Oh I just saw it started working after you went into the control cavity and poked around- theres where the problem is- a bad joint- maybe a burned pot – a cold solder joint

Hard to say without having the guitar in hand

 

[marmatkat]

Re: P-90 now has 1/2 output

The most important is that your pickup works again: don't touch it no more, cross your fingers and enjoy your guitar [but of course, you can bring it to a guitar tech too, if you want to exorcize definitively any risk].

My thinking exactly. :bigthumb:

 

[freefrog]

Re: P-90 now has 1/2 output

FYI Here's the email I got from Jason Lollar :

Let me just quote a few of his words:

<<one thing that happens when the control cavity has grounding paint in it if any of your wires touch that or solder points youll ground out or if you have a stray wire that’s pulled away from the strands you can have odd things happen.>>

The first explanation was a part of my reasons to say "more later maybe" (I had started to evoke that in my previous answer yesterday morning but lacked of time to make it really clear so I've cancelled it; and anyway, I did not see conductive shielding paint in your pickup cavity... but I might be wrong). The second explanation itranslates exactly what happened to me once with a stack pickup in as Strat. I needed a jewel magnifier to detect it. :-/

All that being said, I stand on my initial statements: if a solder joint is squashed to the point to become really thin and/ or if it hides a broken section of insulated wire whose ends still hardly touch each others, it can cause the "series capacitor syndrome" that I described.

IME.


Now and once again: I'm glad to see your problem solved for the moment and wish you to enjoy with your nice axe (among other guitars, I've also a Hamer with P90's. It's a XT and not a MIA but still a really good instrument).

 

[marmatkat]

Re: P-90 now has 1/2 output

> ... I did not see conductive shielding paint in your pickup cavity... but I might be wrong).

I thought the gray paint was that.

> Now and once again: I'm glad to see your problem solved for the moment and wish you to enjoy with your nice axe (among other guitars, I've also a Hamer with P90's. It's a XT and not a MIA but still a really good instrument).

 

[freefrog]

Re: P-90 now has 1/2 output

> ... I did not see conductive shielding paint in your pickup cavity... but I might be wrong).

I thought the gray paint was that.

Yes, it is!

I was talking about the cavity where the pickup itself is installed: according to your first pic above, it doesn't seem to be shielded with paint under the foam. But again, my old eyes might be wrong, knowing that I see your pics on a tiny screen... ;-)