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Basic: what am I doing wrong testing pup resistance?

Discussion in 'Pickups & Electronics [BG]' started by 1bassleft, Feb 9, 2013.

  1. 1bassleft

    1bassleft

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    With my bought-used Ric pup, I got the works DMM and put a probe on each of the two wires and got a big, fat "1". SGD luth kindly replied and, no, I wasn't allowing my body in the way.

    So, back at home, I tried my store-bought DMM and got the same result. Then I tried a BNIB Kent Armstrong P pup and also got a "1". Finally, an old Japanese bass with a 6-pole pup is lying around and, holding the probes steady on the pot tags where the wires are soldered I get a fairly consistent 4.3k.

    I'm going a bit half-crazy and wondering if I've got two dud pups (the Jap bass I know works) or I'm doing something stupid. Any thoughts? I suppose I could put the Ric under a bass, tape the (ridiculously short) wires to the tip and sleeve of a jack and see what comes out of the amp when I hit a string - but I'll have to wait as it's nearly 4a.m. here :scowl:
  2. GlennW

    GlennW Supporting Member

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    As far as the DMM goes, have the ohms scale set to 20K to measure MOST pickups.

    Some pickups (like the Gibson mudbucker, Guild HB's, and the Fender Tele Bass HB) are wound hotter and the DMM scale needs to be set accordingly. I've bought some "dead" pickups off ebay which were fine; the seller probably took readings on the 20K setting, so he thought they were dead.

    To see if your pickups work is easy.
    Forget the meter.
    Plug one end of a cord into your amp.
    Take the other end of the cord and clip/twist/whatever the ends of the pickup leads to it; one lead to the plug tip, the other lead to the plug sleeve.
    Turn on your amp.
    Gently touch the poles with something like a key or a screwdriver. You should hear a definite click or pop through the speaker. That means it's alive.
  3. 1bassleft

    1bassleft

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    Thanks Glenn,

    I had the DMM set to 20k, as I was expecting around 10k (the actual value matters not a jot, just wanted to know it's a worker) but got the "1" on that (and the 2k, 200k, 2M). I'm a bit confused by your follow-up sentence, unless you specifically mean "dead" pups that were actually hotter (>20k). I will try the direct approach tomorrow, when it's a sociable hour.
  4. bassbenj

    bassbenj

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    I presume your DMM is auto ranging and "1" means it's out of range which means you are not making contact with the pickup wires. If it's not auto-ranging be sure to try reasonable ranges for readings. (from maybe 1 k to 100 k)

    Since the meter is reading "open" that means that either the pickup is "open" or you aren't making proper contact with the wires. Best way I've found to test pickups is to simply solder the wires to a loose jack. One to the body tab and the other to the tab that touches the tip. This is much easier and more likely to be making a good contact than simply trying to clip the wires to the end of a guitar plug. Use the screwdriver test.

    If it's still open you'll have to carefully trace the wires back to see if something is broken somewhere. It may or may not be easily fixable.

    Short wires are no problem just get some shrink-tube assortment at Radio Shack and solder on extension wires. Then cover the joint with pieces of tube and shrink it down with a hair dryer.
  5. GlennW

    GlennW Supporting Member

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    That's what I meant, the Guild HB's were alive and well at 36K.

    When I suggested going straight to the plug I was thinking you were testing loose/uninstalled pickups. If they are already mounted you should be able to use the meter as long as you can get the probes to the solder points on the leads. Better yet would be to carefully hold the probes on the pickup eyelets.

    If you don't get a reading at the ends of the leads or at the eyelets, that's a bad sign, but you might get lucky and the pickup is ok, but a solder joint has become oxidized and won't conduct. If that's the case, just reflowing the eyelets with a soldering iron can fix it. I've bought "dead" pickups like that too.

    Good luck.
  6. 1bassleft

    1bassleft

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    Thanks everyone,
    It is an uninstalled pup (doesn't even have a mounting ring) and I'm touching the probes to the bare wires, trying different ranges. What throws me is getting the same result on the new Kent P (a 3-wire, but no combo seems to work). I'll get some sleep and try the screwdriver test later.
  7. SGD Lutherie

    SGD Lutherie Supporting Member

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    Disclosures:
    Owner, SGD Music Products
    A P pickup should read between 10 and 11k. A Rick pickup would be between 7 and 12k.

    I use an auto ranging DMM from RadioShack (stickers courtesy of my daughter). It lets me know if its in the K or M range.

    As an example, I have this photo I took of an Artec mudbucker:

    [​IMG]

    You can see it says 31.41 kΩ

    Here's a Lane Poor M4.0HB; 7.33kΩ

    [​IMG]

    So your meter should be doing something similar. You don't have it set for continuity, do you?
  8. 1bassleft

    1bassleft

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    I'd have to wait until Monday to properly solder the wires to a jack, but I tried it contacting them as best as to tip and sleeve. Get a hum, but no amplified response to a screwdriver tap nor hovering the pup over plucked strings. Doesn't look lively. If I get the same after soldering, I'll contact Heavy Air pickups here in England; I've read a lot of +ves and they do custom/repair work. Thanks again for all contributions.
  9. T_Bone_TL

    T_Bone_TL

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    One possibility, which is hard to say for sure without pictures - are you connecting to the windings, or to insulated wires connected to the windings? It's common to think that you have a "bare wire" when dealing with magnet wire (pickup winding wire) but it has a thin, clear insulation on it which needs to be scraped off to make contact. If you are connecting to normal wires connected to the windings, this is not your problem, though the problem may be one step back, where the normal wires connect (or fail to connect) to the pickup windings - some, but not all, magnet wire insulation is "solder-through" (it goes away with enough heat to melt solder) others need to be scraped or chemically removed to solder properly.

    Then again, "touching" the wires with the probes may not be making a very good connection - usually some type of clamp, clip or pressure is required to get a decent connection between probe and wire. You can use your hands, as your body resistance is much higher than a pickup (go ahead and measure it on the 2M scale without a pickup) or you can use some type of clip to hold the probe tip and the wire together; or just mash them against a table-top.
  10. GlennW

    GlennW Supporting Member

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    Don't solder the wires to the jack. That's unnecessary and will make extra work and mess.

    Since the pickup didn't work while you were holding the leads to the plug, I'd suggest reflowing the solder at the eyelets next.

    You could also use your meter to check if the magnet wire (coil wire) is shorted to the pole/s. One probe on a lead; then put the other probe on the poles one at a time. If you get a reading while doing that it's time for a rewind or another pickup. Try that with both leads (one at a time) and check all the poles (one at a time).
  11. 1bassleft

    1bassleft

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    Hi Glenn,
    Just to clarify, the pup is not installed at all, just lying in the Jiffy bag. Here at home, I was trying with two hands to hold the miniscule wires out onto tip + sleeve whilst tapping. I was going to take it and a seldom-used patch lead to my workplace and solder it on enough to free my hands properly. I could get it off afterwards and not worry much about it.

    I very much like your suggestion to go wire to pole; like checking the compression on a 4-cyl head. In my ignorance, I assumed that the wire just wound around the whole thing and it would make no difference but I'll definitely try that.
  12. GlennW

    GlennW Supporting Member

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    Hi, that bit about the wire-to-pole test only applies to pickups where the coil is wound directly around the magnets/poles. Over time the insulation can fail and the wire makes direct contact and shorts out.

    If it's a pickup where the poles are encased is the plastic that won't happen, BUT, if the insulation fails, the windings could short out on each other.

    Old Fender pickups sometimes short out on the alnico rods.
  13. SGD Lutherie

    SGD Lutherie Supporting Member

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    Which pickup are we talking about here? A Rick or P bass?

    Old pickups sometimes fail. Fenders fail because the wire is in contact with the poles. With Rick pickups, the neck pickup uses a plastic bobbin, and the bridge has a layer of foam rubber between the wire and poles. But i have seen some old bridge pickups that needed to be rewound. It's usually the ones that were wound with plain enamel, since that insulation gets very brittle after a while.
  14. 1bassleft

    1bassleft

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    It's a Ric hobnail, without any mounting surround. As it happens, I didn't get the chance today to solder anything. I did get my simple DMM out again to try the "wire to polepiece" measurements and one of the wires fell off in a brittle way, revealing a sort of small metal spike. At first, I thought "A-ha, a crusty old wire is the problem", but that evaporated. Probes from the other wire to the spike still give the "1", as does either the wire or the spike to any of the poles.

    Along with the no-noise tap-test or when held over vibrating strings of an unrelated bass, it does look like it's well past my limited capabilities. I could send it to Heavy Air for a look and, if cost-effective, repair:
    http://heavyair.co.uk/custom/

    Their own-make pups are reasonably priced and I've read good things about their service; in the absence of any other experience I'm hopeful that they'd be competent and honest. I do need to spend more time with the Vintage MM copy and think about what I want (this thread is a split-off from my "Ric or Tele?" that you replied to, SGD). If it were a worker, routing for the Ric would be a good step-up in experience from just pup-swapping and a combo I've long wanted to try. If making the Ric work is a heavy expense, I don't want to go ahead on a whim.

    I do very much appreciate the time taken by everyone to offer advice and suggestions; thankyou.
  15. GlennW

    GlennW Supporting Member

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    The "1" reading on the lead-to-pole test is a good sign. That means the wire hasn't shorted to the poles/mags.

    Before sending it off for professional help, I'd try reflowing the solder at the eyelets if you haven't already. You might get lucky.
  16. 1bassleft

    1bassleft

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    Glenn, I understand the first part - no short, good thing, but (apols for sounding noobish), don't follow with "reflowing the solder at the eyelets". I haven't removed the tape wrapped around the bobbin so all I've seen so far is the outer. Can you enlighten me if you have time or direct me to a link?

    Many thanks.
  17. GlennW

    GlennW Supporting Member

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    I'm unfamiliar with your pickup, and it's possible it doesn't have eyelets. Most HB's and P-90s don't, they have the magnet wire twisted around and soldered directly to the leads (sometimes called pigtails), and then taped up for protection.

    Most Fender pickups have eyelets. They look like tiny silver donuts, and the magnet wire is wrapped through the hole and around the bobbin/flatwork a few times; then the lead is stuck into the hole; then it's all soldered together. With this method the lead-to-magnet wire connection is clearly visible. Just look at a P, J, or Strat pickup and you'll see. If your pickup has something like that, heat up your soldering iron and melt the solder that's already there again. This will restore an oxidized ("dead") connection. You can add a touch of new solder if you want, but it really isn't necessary unless the old melted solder wants to go where it doesn't belong.

    If it doesn't have eyelets the same approach might work. It's delicate work, but not that big of a deal if you're careful and can see well. It's not like you'll screw it up, because it isn't working now, and it might be an easy fix.

    Edit: If you try that, don't let the soldering iron linger because too much heat WILL mess up the magnet wire. Melt the solder so it flows, and STOP. Good luck.
  18. 1bassleft

    1bassleft

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    With little to lose, I carefully unwrapped what looks like electrical insulating tape wrapped round and, to my surprise, that's what seems to be holding the remaining, unbroken wire onto the coil winding. That seems to look very good but who's to know? I very gingerly used my probes but still got the "1".

    I'm really out of my depth now and could potentially turn a simple problem into a ruiner with hamfistedness or ignorance. Since it needs fitting into a mounting anyway, I really ought to pass it on to someone experienced.

    Which reminds me - I finally clicked on your weblink, SGD. Blimey, that's lovely stuff you do there. How I wish USPS still did their Global Priority Mail envelope for $9; it used to make all manner of small parts from the US cheap to send but now their lowest ship is the small box at $24. I'll have to try Heavy Air over here but, if the pup's a basket case, that Sidewinder in the Ric housing looks fab.

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