Help me troubleshoot some faulty speakers and/or learn how to read a schematic...

[Joben Magooch]

Hi all. Looking for some help/advice with a non-pedal issue...

I picked up a set of speakers+subwoofer at the local goodwill a few days ago. Klipsch Promedia 2.1 - two satellites and a powered sub. My friend has a set and they're pretty nice sounding in my opinion and only cost five bucks so figured it was worth a flyer.

Well, they're not working. No power to the subwoofer, and the satellite speakers aren't getting any either. For reference, the sub connects straight to AC power. I think some models have an on/off switch, but this one doesn't. The satellite speakers have a few connections - each gets a set of regular speaker wire, and then the "control module" that mounts on one of the satellites connects back to the Subwoofer with a 9-pin DIN connector. The control module has the volume and sub level, as well as a headphone out and line in. It also has a male 3.5mm connector for hooking up to your PC (or whatever) 3.5mm out. There is an LED on the control module to indicate that it's getting power; it doesn't come on at present.

So I cracked open the subwoofer to take a look at the PCB(s) and see if anything looked amiss. From first glance, I couldn't see anything too wrong. Some of the stuff is "gooped" (I don't think it's in the "obscure so people won't copy" style but rather "Slather glue over everything so it doesn't move around," lol) which makes it hard to tell, but there was noting noticeably off - nothing burnt or scorched, no bulging caps, visually seems okay. I did realize that this model also uses an internal through-hole fuse rather than a "typical" external and/or glass tube fuse, so that was a bit odd.

Anyways, here's where it gets a little stupid. I'm impatient and figured I was already only out five bucks so decided to maybe try something dumb. I figured perhaps the fuse was blown and that should be my first thing to check. But I'm fresh out of through-hole fuses (lol) and didn't want to wait to get some ordered just to try a new one out. So, don't crucify me, but I just grabbed a spare resistor and jumpered the fuse spots with it. Hooked back up to power and still nothing, BUT as soon as I plugged in the 9-pin DIN connector it got power and could hear the sub "thump" on....But then the resistor-jumper I put in started glowing red-hot so I yanked the power ASAP. I don't really know what exactly I got from this highly-scientific and perhaps misguided experiment but it does seem like maybe I'm in luck and it's just needing a new fuse installed? I'm going to order some and hope for the best.

Beyond that however I'm wondering what would be the next thing(s) to check if replacing the fuse doesn't sort it out or if they keep blowing or something. I have found a few schematics floating around for this set, but really don't know how to read a schematic super well. Maybe I'm going to reveal my own ignorance but it seems more or less like a big connect-the-dots with the various symbols (zigzag line for resistor, two perpendicular lines for capacitors, etc) showing the various components? I guess I'm just wondering if anyone has any good resources for "How to learn to read schematics for dummies" or something so I can have a better idea of where to start troubleshooting if simply replacing the fuse doesn't work.

Anyways, that's all for now I guess. I'm hoping the whole set isn't fried or just a wild goose chase but it was cheap enough so I figure if nothing else it's something to learn a bit on and best-case scenario there's an easy fix that gets me a nice new set of speakers for very minimal investment.

 

[Alan W]

I really think that there’s a reason the fuse blew in the first place, and just replacing it won’t help—but it’s only the cost of a fuse, and is absolutely worth trying. You did the visual check already, and that goop can really be a challenge. So, it comes down to if a new fuse doesn’t do it, are you willing to degoop as needed to be able to do some continuity and power tracing? It’s almost definitely in the power supply section, which may even be on a separate board. You could solder some jumpers onto a small fuse and try that while you’re waiting for the through hole fuses to come in.

 

[Alan W]

I just reread your post, and should have read it more carefully. I also looked at the schematics. Please proceed with caution—it’s an AC powered system, and since they’ve got a 2amp fuse in it, there’s some dangerous current in there. Do you have a multimeter, and understand the basics of it? Ideally with a probe that you can attach an alligator clip to? I always try to practice the “sit on one hand” approach when poking around AC powered stuff—clip one probe somewhere, use one hand to move the other probe around, and keep the other hand in you lap, your pocket, or sit on it. Getting snapped at by current on one hand will be felt, but wont be anywhere as dangerous as having it pass through from one hand to the other.

You’re reading of the symbols in correct, but there’s also a bunch of diodes, transformers, etc. in there, and many places where the circuits use connectors to patch other places in, so it’s not the easiest board to look at and understand, unless you have a basic sense of what all the parts do (at least typically). So—please be careful!

 

[Joben Magooch]

Please proceed with caution—it’s an AC powered system, and since they’ve got a 2amp fuse in it, there’s some dangerous current in there.

Definitely. Certainly far from an expert, but I do know at least enough to be reasonably safe. I have done a little work on tube amps in the past which I assume would more or less carry similar risks...

Do you have a multimeter, and understand the basics of it? Ideally with a probe that you can attach an alligator clip to?

I do have a meter and am *mostly* familiar with it, at least as far as the basics go - measuring voltage, resistance, amps, continuity, etc...

I always try to practice the “sit on one hand” approach when poking around AC powered stuff—clip one probe somewhere, use one hand to move the other probe around, and keep the other hand in you lap, your pocket, or sit on it. Getting snapped at by current on one hand will be felt, but wont be anywhere as dangerous as having it pass through from one hand to the other.

Yeah...Maybe I will be needing to order myself some leads w/ clips. As it stands I've only ever had/used the "probe" kind. (Well, that and I once used some jerry-rigged apparatus with alligator clips and a resistor to discharge amp caps because it felt less sketchy than just using a screwdriver to send them to ground, but...otherwise, no )

You’re reading of the symbols in correct, but there’s also a bunch of diodes, transformers, etc. in there, and many places where the circuits use connectors to patch other places in, so it’s not the easiest board to look at and understand, unless you have a basic sense of what all the parts do (at least typically). So—please be careful!

I guess that's more or less what I'm getting at - kind of know the absolute most basic points of it, but trying to get a bit beyond that. For instance, I saw over on some Klipsch forums some suggestions that basically said to trace the power rails to figure out where/why power isn't going to the right place and/or is sending too much thru the fuse or whatnot...