Mogens

Well, you gotta obey the rules.

I didn't mean to post any more. But there is just so much truth in what you said. I definitely wouldn't have gotten as good a hug and high fives from my daughter if it had just worked right away. I have actually made a saying and taught it to my kids. Roughly translated from danish: if you are always glad then you are never truly glad. Meaning that without downs there can't be ups. She immediately called it out when I read your message to her. (Sense of fatherly pride.) The whole thing was surely an educational experience. And by now only the joy of the sweet music reminds.

Would you imagine. Everything works when you just hook it up correctly 😁 I still have this weird feeling of both embarrasment and joy. She's playing now and all is well. Thank you all once again. What a lovely community.

OH MY FREAKING DOG!!! When I studied the original circuit in preparation for remounting it I noticed a couple of cables were coax. So it turns out that the pups output a separate ground as well as a ground on the shield of said coax cable. I had just soldered the entire coax as one to the signal side of the balance pots. I did actually notice a little gunk but I had just switched solder, so I just assumed it was flux or something. I hurriedly cut one off, stripped it properly and connected it straight to the amp. SOUND! It works. The pup has a resistance of 7 k-ohm, which is much more reasonable. This is by far the most embarrassing mistake I have ever made in DIY electronics. But Oh my I'm so happy at the same time and so is my daughter. I can't do it right now but I will try and just wire it up correctly with the new preamp, and if that misbehaves (which it probably wont) I will install the old one. A million thanks to everyone who wrote here. I don't think I would have discovered my error without you. I will report back if the new preamp turns out to be compatible or not.

So many helpfull people here. Thanks. I will see if I can get arround all suggestions and questions. The battery is new and 9 volts is delivered to the main circuit. When no jack is inserted I get arround 8 volts across signal/ground on the jack-socket. 0 when a jack is inserted. That makes me think the board detects the insertion correctly. I have no reason to think the electronics are defective or incorrectly installed. If I short the balance pot's output with some metal I can produce noise. So I assume everything up until there works. I have no idea how the bass has been stored. But degaussing would probably involve some big magnet which I don't think the previous owner had. If I move a magnet across the pickups I feel resistance but no sound is produced. If I connect one of the pups directly to the amp I just get at loud buzzing. Pups with out of the ordinary specs sound very likely like the reason now. I will try and refit the old preamp. Though it will take me some time as I was very quick with the snips when I took it apart. The pups have these model numbers according to the manual, though I couldn't find any specs on them: QC460500 and QC460600. I can't easily get to the backside of the pups to check the connection. But as my previous post I would expect "Open circuit" on the multimeter if the wire had fallen off the coil.

Two wires out from each of the pickups, yes. I would also think it odd for the pickups to both be burnt out. And if they did I would either think the wire had burnt over - open circuit - or the insulation had melted - very low resistance. But I measure a very high resistance through them. The pickups are completely unbranded on the front. But pictures I find online of the model of bass often has some brand printed on them. So they might not be original. Could they have been repaced with active pickups? Would that make sense? How can I check it? The electronics I bought says it supports both passive and active pickups. But I see no way to change it. Like a switch or different wiring. As for preference. At this point cheap and functional are the keywords. She's a newbie on the bass and just need to be able to practice. And she's on a childs budget, even though I can chip in some if need be. I'm sorry for being so dumb. I just want to help her get a functional instrument.

It seems to me both pickups are gone. Is that comon? What are the parameters I need to be aware of when shopping for new ones?

Thank you for the reply. It goes in the same direction as Paul the Plug above.

Yeah I thought so. I'm not sure if I read correctly. I have the multimeter at 2000k-ohm. At 200k-ohm I get 1/open circuit. It's pretty sad for her if she need to buy new pickups. Then she'll be so deep into this instrument she could have bought a new one instead.

I'm not sure if I understand it correctly. If I connect the pickups directly to the cable going to the amp using alligator clips I get a buzzing but no response to strumming. Should I connect the pickup wires directly to the socket inside the bass while the battery is connected?

Tried it and can confirm those measurements.

Hello I'm new here. I hope someone is willing to try and help me out a bit. My high school daughter bought an old Yamaha rbx760a. She in high school and It's her first bass. She mostly plays ukulele but also has a couple of guitars and a piano. Her band needed a bass player and she wants to be able to practice at home. The bass was sold a defect with a shut jack-socket. When I got to look at it the pots were very worn and I decided for her it would be best to replace the electronics as well as the socket. So I bought a cheap set: artec se2 which seems compattible https://www.thomann.de/dk/artec_se2_basselektronik.htm The installation was pretty straight forward: I have grounded everything (bridge, backside of the volume pot and ground on the main circuit board)to the sleeve of the jack. But it doesn't work. There is absolutely no response in the amp from strumming the strings. There is very little humming. It makes a lot of noise if I plug or unplug the battery. I have tried reversing the polarity of the signal out. I have tried reversing the polarity of the pickups. I have tried removing the ground wires from the sleeve, which results in a lot of humming or even buzzing. If I unplug the balance pot and touch the pins on the mainboard I can produce noise in the amp. The balance pots measures correctly with a multimeter. It seems to me the only thing left is the pickups When I measure their resistance it comes out to 240k and 1000k if I read the multimeter correctly. I have no idea what to try next. Oh at some point we were able to produce some horrible noise from the pickups during trial and error but I have no idea how. She's really already maxed out her budget. But if the pickups are both broken we'll figure out something. But I need to exhaust all other possibilities first. Can I test them by wiring them up directly to the amp? in series with a battery? Which voltage? Any other suggestions. I (and her) will be so grateful for any help you can provide. Best Regards Mogens from Denmark.