Walker Posted October 12, 2019 Share Posted October 12, 2019 Hoping someone can help with this. I've lost volume on my P bass. I plugged in my Fender Road Worn P (which has a StewMac Golden Age Pre-wired Harness for P-Bass) yesterday and I had no volume. It's been working fine and has just been hanging on the wall, so nothing obvious has happened that could have caused this. Signal is registering on my tuner, and if I crank the volume to max on the amp, I can just about hear some hear the notes among the hiss. If I turn the volume down, I can't hear it (as expected), but if I turn the volume back up again and turn the tone down, I can't hear it either. With both pots to max, I can hear my plucking. Tone pot reading 241k - 485k Vol pot reading 0 - 241k All wiring is solid with continuity as expected. I'm at the very limit of my limited knowledge and I'm at a loss! Any idea why this could be? Cheers Chris Quote Link to comment Share on other sites More sharing options...
caitlin Posted October 12, 2019 Share Posted October 12, 2019 Assuming this to be a daft question but since in debugging NO questions are daft... it's not the amp, is it? I trust it's been checked with other guitaren? Otherwise, the tuner doesn't have a microphone that could be hearing notes that way? is something shorted to ground? Quote Link to comment Share on other sites More sharing options...
Walker Posted October 12, 2019 Author Share Posted October 12, 2019 Good questions! The tuner is in my Kemper, so through the cable, my other bass and guitars work fine, I've tried other cables and amps. If something was shorting, could that affect the volume? Is that tone pot reading what it should be? I'm not sure how the cap would affect the numbers on that pot (if at all)! I'm cluless! Quote Link to comment Share on other sites More sharing options...
caitlin Posted October 12, 2019 Share Posted October 12, 2019 That some signal at all reaches the amp means that you *have* a signal path, but something is 'attenuating' it, which is what the variable resistors do anyway, the couple the signal to ground through some magic bits of tat. that the signal is not GONE means there isn't a hard short to ground, but something like the dielectric breaking down in a cap or in the jack socket MIGHT create a resistive path to ground. I'm new to this forum and I don't think anyone's twigged that I'm an idiot yet 1 Quote Link to comment Share on other sites More sharing options...
Walker Posted October 12, 2019 Author Share Posted October 12, 2019 Is there any way to test a cap or shall I just solder a new one in and see? Quote Link to comment Share on other sites More sharing options...
caitlin Posted October 12, 2019 Share Posted October 12, 2019 There are ways to test them but they're complicated and magic, mr carlson's lab on youtube goes into lots and lots of detail about 'how this stuff works' but you need a magic tester to test them properly and i don't even know anyone who has one of those. If you had a wiring diagram you could try bypassing parts of the circuit to narrow down where the broken bit is, perhaps? Here's something i don't know: can one connect a pickup directly to the output of the guitar? bypassing the volume and tone circuitry entirely, I can't think of any reason why not... that would allow us to see if we can get any life from it at all. Quote Link to comment Share on other sites More sharing options...
Walker Posted October 12, 2019 Author Share Posted October 12, 2019 I just ran the meter over again to see if your theory about dielectric breaking down on the jack and I'm getting continuity across the two tabs on the jack. I'm assuming that's not right?! Quote Link to comment Share on other sites More sharing options...
caitlin Posted October 12, 2019 Share Posted October 12, 2019 I think not! Got a spare you could swap in? we may have it! Quote Link to comment Share on other sites More sharing options...
Walker Posted October 12, 2019 Author Share Posted October 12, 2019 I'll desolder the jack and see if I still get continuity across the wires and I can check the jack in isolation. I'll be back and let you know! When I was 20, if you'd told me this is how I would be spending my Saturday nights! Thanks very much!!! Quote Link to comment Share on other sites More sharing options...
KiOgon Posted October 12, 2019 Share Posted October 12, 2019 Well I've never seen a more stupid way of fitting a cap.! If the long leg, earth side of that cap. ain't touching the 'unused' tag on the tone pot when fiited to the scratch plate, I don't know! Should have gone to specsavers 2 Quote Link to comment Share on other sites More sharing options...
Walker Posted October 12, 2019 Author Share Posted October 12, 2019 It must be the volume pot... I'm getting continuity between the case and the middle tab and there is nothing attached to it except the white wire that I desoldered from the jack. I've no idea how a high quality CTS pot could just go!? I'll swap it out tomorrow once I've had a rummage in my parts box. Thanks again for the help. Really appreciated. Enjoy the rest of Saturday night! 1 Quote Link to comment Share on other sites More sharing options...
caitlin Posted October 12, 2019 Share Posted October 12, 2019 in your second picture the top pin on the left hand pot (which is the one i think is the volume) is connected to the case of the pot (ground) so you're measuring from the middle pin (wiper) through the resist out of that upper pin and through the case. I *expect* that if you measure the value of that resistance and wiggle the pot, the value will change. Enjoy your weekend too. Quote Link to comment Share on other sites More sharing options...
Walker Posted October 13, 2019 Author Share Posted October 13, 2019 Thanks for your help with this... caitlin... I *expect* that if you measure the value of that resistance and wiggle the pot, the value will change. Yes, that's what's happening Meddle... I've checked the points you kindly suggested and everything is clear. Can I just check I've got this right and my extremely limited electronics knowledge isn't even worse than I thought! If I do a continuity test from the case of the pot (ground) to the middle tab, there *should* be NO continuity, so I shouldn't hear a beep! In fact, if I do the same continuity test on any black to white wire on the harness, I shouldn't hear a beep. Is that correct? That seems to be the case on my other bass, which I've just checked. Quote Link to comment Share on other sites More sharing options...
caitlin Posted October 13, 2019 Share Posted October 13, 2019 pinching someone else's picture but i hope that's ok because they get their advert out of it: you can see that if you trace from the body of the jack, up to the volume pot chassis, the right side pin is grounded that goes into the pot and connects to one end of the resist. there's 'some distance of resist' before you reach the 'wiper' which is connected to the middle pin. you can then trace from the middle pin back down to the tip of the output jack... I think this is the resistance you're seeing. We're dealing with AC current, not DC and 'leaking to ground' is what all these systems do deliberately to attenuate whatever frequencies they want to act on. Quote Link to comment Share on other sites More sharing options...
Walker Posted October 13, 2019 Author Share Posted October 13, 2019 Ah, I see, so I should expect to see a positive continuity test if i touch the two sides of the jack with my meter probes. I didn't know that. It doesn't happen on my other bass, so does that mean a damaged component could be leaking too much? Sorry if I'm being dull, but I'm finding this fascinating and trying to understand! Quote Link to comment Share on other sites More sharing options...
itu Posted October 13, 2019 Share Posted October 13, 2019 20 hours ago, Walker said: I've no idea how a high quality CTS pot could just go!? There is "high quality" and a carbon track pot in the same sentence. Funny. You want quality, buy a conductive plastic or cermet track pot. Brands to look for: Bourns, Vishay... 1 Quote Link to comment Share on other sites More sharing options...
Walker Posted October 13, 2019 Author Share Posted October 13, 2019 Thank you. Quote Link to comment Share on other sites More sharing options...
Bassalarky Posted October 14, 2019 Share Posted October 14, 2019 Just to answer the question above, you certainly can connect the pickup directly to the output jack - a quick and effective way to reassure yourself that the pickup is working. You can measure capacitors with suitable meter but to be accurate you would have to remove it from the circuit anyway (or at least one leg). I'd suggest wiring the pickup direct, if that works wire the vol pot, if that works add the tone pot. Hope you get it sorted. 1 Quote Link to comment Share on other sites More sharing options...
Walker Posted October 22, 2019 Author Share Posted October 22, 2019 It was one of my pups. I eventually isolated and tested both and one of the was dead. Beat's me how a pup can just 'go', unless it had a knock? Visibly it was fine, everything connected and decently soldered. Oh well, £100 for new pups and £6 for a new pot I never needed. Up and running again. Thanks for the help everyone Quote Link to comment Share on other sites More sharing options...
caitlin Posted October 22, 2019 Share Posted October 22, 2019 A pup isn't much more than a coil of wire around a metal core, they fail the same way any winding does, either open or short. If the wire cracks anywhere along the length, electricity is gone from it. If it shorts *somewhere* then performance will suffer in weird ways. You can of course rewind a pickup if you can be arsed and can count to quite high numbers or have a stepper motor you can employ Quote Link to comment Share on other sites More sharing options...
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