CurtPalme.com Home Theater Forum

Untuned · Joined: 03 Dec 2011 Posts: 93 Location: Pooler, GA

I’ve got an old subwoofer that quit working. My electronics know-how is very basic; nothing is too obvious for me!

It’s a Jamo SW600, impossible to find any info on it, and I don’t have any manuals for it. It has a separate little box that will accept several inputs (Sub signal in, L/R in and out [RCA and speaker posts]) and pots to adjust level and crossover, and then sends the signal via coax to the sub. It was working fine, then I brought it to my buddy’s house, and it wouldn’t work. I brought it home and it wouldn’t work either. There is a 5A fuse accessible from the outside: it’s ok. I removed the screws holding the plate to the cabinet to look for any obvious fried parts, and saw that there were two more 5A fuses. One of them had popped, so I replaced it. As soon as I had turned everything back on again, the same fuse popped. Anything obvious that I should be looking for?

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Sounds like when you moved it some metal part might have shorted something out. You would have to really look close for any metal part or any other burn marks.

Athanasios

ecrabb · Posted: Wed Oct 09, 2013 8:05 pm Post subject:

Leave the external box out of the equation for the time being; it's just an active crossover unit.

See if you can unplug one of the the leads to the sub driver (or take the amp completely out of the enclosure), then apply power again and see if the fuse still blows. Use caution if you're going to be plugging in the amp and have the amp power supply components exposed.

From reading a few of the threads where Mac or Curt has chimed in, it's most likely a blown amp output transistor, or a the driver itself could have developed a short in the voice coil, possibly from getting moved. If it still blows the fuse with the driver disconnected, then you'll have to get Curt or another tech to help you troubleshoot, and without any electronics troubleshooting experience or tools, it could be more than you want to bite off.

SC

Jeremy112 · Joined: 28 Sep 2006 Posts: 2649 Location: Fond du Lac, WI

You have a shorted power output chip in the amplifier, that's why the fuse keeps blowing right away. It should be a relatively easy repair for someone like myself. For someone who has basic knowledge, it isn't the easiest thing to do.

Surprised to see another Jamo user at all, we are quite a rare breed, Smile

Untuned · Joined: 03 Dec 2011 Posts: 93 Location: Pooler, GA

Yeah, it's kind of a cool sub: it has two drivers facing each other doing the push-pull thing.

So this power output chip in the amplifier, would you happen to have a schematic fellow Jamo enthusiast? What do these things look like?

Untuned · Joined: 03 Dec 2011 Posts: 93 Location: Pooler, GA

Update:

So this sub has been collecting dust and I decided to take another stab at it.

I plug it in, and turn it on, give it a source, and it does not blow a fuse. I can hear sound, but only if I get very close to the speaker - it's very faint. So I took an external amp and hooked it up to the sub: it works.

So the amplifying circuit is obviously not working; am I still looking at a blown power output chip? I did find a schematic finally, I've put it in attachment. Looking at the board, I found a TL084CN; is this the chip in question? There are no other components that look visibly defective or burned out. There is a voltage drop across the caps also.

Sure, I could run it off an external amp, but I'd like it to keep the original amp, and I'm interested in learning in the process. Any other hints are greatly appreciated! I found some pics of the sub, not taken by me, but identical to mine.

**Curt Palme** · Posted: Wed Oct 08, 2014 4:32 pm Post subject:

Offhand, I'd say an open capacitor in the signal chain. This is where a scope would help.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

As with any device not working properly the first thing you would want to check are your source voltages. Test them and see what you have.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

pcmerc · Joined: 17 Feb 2015 Posts: 3

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

pcmerc · Joined: 17 Feb 2015 Posts: 3

Actually, mine is burned up. So no, I can't tell the color codes on it.
Thanks macgyver! Very Happy

I have an old jamo SW600 as well that just took a crap. Looks like the 2 6800uf 50V caps died as did R36.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

ecrabb · Posted: Tue Feb 17, 2015 4:41 pm Post subject:

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Yes, the -22v is on the shield part of the RCA connector. That sends power to the input box and is regulated to power the ic's in it. If connected to a regular preamp out of a device it would be trying to power up the chassis.

And I completely agree it is the dumbest thing they could of done.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

This is the connector.

ecrabb · Posted: Tue Feb 17, 2015 11:14 pm Post subject:

Thanks, Mac. Yeah, that makes no sense to me. I know it's elegant from a design standpoint (single cable), and at least it's labeled what it's fore, but if they were going to use an RCA jack (which is standard on almost every powered sub I've ever seen) in such an unconventional way, then I would think a warning symbol with a simple note about not connecting it to anything but the Jamo control/crossover would have made a whole lot of sense. Such a warning note on the sub itself would have been especially apropos since they know damn well when they sell the things, they're going to be kicking around for years, changing hands, and that in the vast majority of circumstances, the manuals will be long gone.

Cheers,
SC

pcmerc · Joined: 17 Feb 2015 Posts: 3

Thanks again MacGuyver655! Parts received today, replaced the 2 6800uf 50V caps & the 820 ohm R36. Subwoofer lives!