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Untuned
Joined: 03 Dec 2011 Posts: 89 Location: Boucherville, Qc
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Link Posted: Wed Oct 09, 2013 5:22 pm Post subject: Jamo subwoofer died - HELP! |
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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?
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Nashou66
Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY
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ecrabb Forum Moderator
Joined: 13 Mar 2006 Posts: 15909 Location: Utah
TV/Projector: JVC RS40, Epson 5010
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Link Posted: Wed Oct 09, 2013 8:05 pm Post subject: |
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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
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Jeremy112
Joined: 28 Sep 2006 Posts: 2645 Location: Fond du Lac, WI
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Link Posted: Wed Oct 09, 2013 9:34 pm Post subject: |
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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,
_________________ When I'm asking for a Model number, that doesn't mean I'm asking for a nude photo with your number on it
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Untuned
Joined: 03 Dec 2011 Posts: 89 Location: Boucherville, Qc
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Link Posted: Thu Oct 10, 2013 1:04 am Post subject: |
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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?
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Untuned
Joined: 03 Dec 2011 Posts: 89 Location: Boucherville, Qc
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Link Posted: Wed Oct 08, 2014 4:24 pm Post subject: |
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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.
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Curt Palme CRT Tech
Joined: 08 Mar 2006 Posts: 24303 Location: Langley, BC
TV/Projector: All of them!
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Link Posted: Wed Oct 08, 2014 4:32 pm Post subject: |
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Offhand, I'd say an open capacitor in the signal chain. This is where a scope would help.
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macgyver655
Joined: 22 Aug 2007 Posts: 8508
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Link Posted: Wed Oct 08, 2014 7:41 pm Post subject: |
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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.
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macgyver655
Joined: 22 Aug 2007 Posts: 8508
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Link Posted: Wed Oct 08, 2014 7:42 pm Post subject: |
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Curt Palme wrote: | Offhand, I'd say an open capacitor in the signal chain. This is where a scope would help. |
Scopes are for sissy's.......
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Nashou66
Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY
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pcmerc
Joined: 17 Feb 2015 Posts: 3
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Link Posted: Tue Feb 17, 2015 3:59 pm Post subject: |
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Untuned wrote: | 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. |
Can you tell me what color codes are on R36, please?
The schematic you have attached does not look completely correct. It is missing stuff compared to my pcb board layout on my SW600 unit.
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macgyver655
Joined: 22 Aug 2007 Posts: 8508
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Link Posted: Tue Feb 17, 2015 4:08 pm Post subject: |
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pcmerc wrote: | Untuned wrote: | 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. |
Can you tell me what color codes are on R36, please?
The schematic you have attached does not look completely correct. It is missing stuff compared to my pcb board layout on my SW600 unit. |
Why, you don't think yours is 820 ohm?
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pcmerc
Joined: 17 Feb 2015 Posts: 3
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Link Posted: Tue Feb 17, 2015 4:16 pm Post subject: |
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Actually, mine is burned up. So no, I can't tell the color codes on it.
Thanks macgyver!
I have an old jamo SW600 as well that just took a crap. Looks like the 2 6800uf 50V caps died as did R36.
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macgyver655
Joined: 22 Aug 2007 Posts: 8508
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Link Posted: Tue Feb 17, 2015 4:17 pm Post subject: |
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ecrabb wrote: | Leave the external box out of the equation for the time being; it's just an active crossover unit.
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Well since this thread is still being looked at for info then I need to correct this.
The input box "has" to be used with the sub. It is part of the signal chain. You "cannot" plug a preamp signal directly into the sub box RCA jack. You could damage your preamp if you do.
So "always" use the input box with the sub.
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ecrabb Forum Moderator
Joined: 13 Mar 2006 Posts: 15909 Location: Utah
TV/Projector: JVC RS40, Epson 5010
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Link Posted: Tue Feb 17, 2015 4:41 pm Post subject: |
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macgyver655 wrote: | You "cannot" plug a preamp signal directly into the sub box RCA jack. You could damage your preamp if you do. |
How do you know this, Mac? Back when I chimed in on this, I couldn't find a manual, nor can I now. What is it on the schematics that indicate damage could occur to connected preamp? Is it the -22v on the signal input? If so, then I'd assume they manufactured the sub with a non-standard input cable to prevent connecting a preamp directly, or at least affixed a warning label if they used a standard coax connector.
Just trying to understand.
Cheers,
SC
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macgyver655
Joined: 22 Aug 2007 Posts: 8508
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Link Posted: Tue Feb 17, 2015 5:40 pm Post subject: |
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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.
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macgyver655
Joined: 22 Aug 2007 Posts: 8508
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Link Posted: Tue Feb 17, 2015 5:44 pm Post subject: |
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ecrabb wrote: | If so, then I'd assume they manufactured the sub with a non-standard input cable to prevent connecting a preamp directly, or at least affixed a warning label if they used a standard coax connector.
Just trying to understand.
Cheers,
SC |
Oh, forgot to answer this. No label with warning. Standard cable with RCA on both ends.
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macgyver655
Joined: 22 Aug 2007 Posts: 8508
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Link Posted: Tue Feb 17, 2015 6:06 pm Post subject: |
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This is the connector.
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ecrabb Forum Moderator
Joined: 13 Mar 2006 Posts: 15909 Location: Utah
TV/Projector: JVC RS40, Epson 5010
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Link Posted: Tue Feb 17, 2015 11:14 pm Post subject: |
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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
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pcmerc
Joined: 17 Feb 2015 Posts: 3
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Link Posted: Sat Feb 21, 2015 3:22 am Post subject: |
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Thanks again MacGuyver655! Parts received today, replaced the 2 6800uf 50V caps & the 820 ohm R36. Subwoofer lives!
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