Sub Woofer replacement and connection

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Old 08-12-18, 10:54 AM
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Sub Woofer replacement and connection

Our home theater sub woofer pooped out a few weeks back. Original (JBL) was an 8" 100w. Did all the trouble shooting possible and concluded that a component, possible a large cap, may have finally given out after 15 years. Shopping around for decent new or used but I have a question.

The receiver is a Sony STR-DE695. The only output for the sub is an RCA labeled "Sub woofer". (Go figure) Receiver specs for this output State "Analog Output; 2V; Impedance 1kilohms".

The original JBL self-powered sub had Raw cable I/O as well as, Line level In L/R and LFE Input (RCA). The LFE input was used & worked great for all audio sources.

Many subs I've looked at so far have raw cable I/O ("high level") and a pair of RCA Line in L/R.

So...is it possible to adapt to our system?

As a "postscript", I may get brave enough to take it apart and do some "interior" trouble shooting as i have repaired a Crown D150A amp on my own in the past.

Thanks in advance for any input.
 
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Old 08-12-18, 11:39 AM
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i have repaired a Crown D150A amp on my own in the past.
Be careful..... you're showing your age there.

I'm a sound man from way back. D150A and 300A's. Went from them to Microtechs..... to Macrotechs and now to a stack of K2 digital switching amps. Crown is king in pro amps.

You need any type of powered sub. That means the sub has an internal amp like your old JBL did. If you buy a passive sub then you'd need to buy a sub amp too as your receiver only outputs line level SUB signals.

Break that JBL open and post the model number for it.
 
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Old 08-12-18, 02:37 PM
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Ya got me..."showing my age". LOL The D150A is still in svc in the studio, but developed a barely audible "chirp" when powering down. (Another topic)

Looking at powered subs. Even a 60w should do the trick. The main question is/was can I split that single Sub Woofer out on the receiver using an RCA "Y" and use the L/R inputs on a powered sub? Guessing yes.

As for the JBL sub that's out, I'll break it open when time allows and post the Model number. The "Surround Cinema Speakers" set that I bought at the same time as the receiver is Model SCS136. (A JBL Set) Not sure if a set model # will help.

Thanks for the reply PJmax!
 
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Old 08-12-18, 05:15 PM
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Yes.... you can use an RCA Y cable to drive both sub inputs. Many subs have a way of accepting a mono input. Sometimes it's just using the left channel.
 
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Old 08-13-18, 11:37 AM
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Thanks Pj! Y cord would have been my guess.

Number on back of case is SUB136.

Broke open case and amp section. Two numbers on main PCB board:

101ASUB135PE
104SUB13500

Couldn't see anything out of the ordinary like a component discoloration or burn. No idea on how to trouble shoot. It's been ages.
 
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Old 08-13-18, 11:56 AM
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See if this service manual covers your sub....
scribd/doc/185062696/SCS135-136SI-145S-Service-Manual

The first place to start is at the power supply. Check for the 15v supplies.
I'm seeing a fuse in the incoming line too.
 
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Old 08-13-18, 07:17 PM
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Sure looks like the right one. Haven't done any serious troubleshooting in years though. Quite honestly, I got lucky with that D150A years ago. The fried component was obvious.

I might tinker with the sub when we get back in town, but a replacement sounds much easier.

Thanks again PJ!
 
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Old 08-13-18, 08:35 PM
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If you decide to pursue a repair..... I can guide you through it.
 
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Old 08-13-18, 09:19 PM
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I DO appreciate your offer! Might take you up on it soon.

Thank you, and take care.
 
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Old 08-19-18, 10:08 AM
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Pjmax: Thank you for offering to troubleshoot! Before moving ahead I thought it would be a good idea to fill you in what happened before the sub went out.

We had a power outage a few weeks back. Huge branch came down on electric wires in yard. Yanked the wires right off the wall and out of the service mast leaving it bent at an angle. Electric company came out, got the live wires out of our yard, re-attached wires to wall but couldn’t restore power until an electrician repaired the mast. Got it repaired and AC restored.

When the breaker was pushed for the outlets powering the entertainment center, it sounded like a bear was pounding on the wall in the corner where the sub is in our family room. Took a while to figure out what the heck it was. The sub! Eventually the sub was just emitting an intermittent static-type sound. (Hard to describe) Unfortunately there’s no surge protection on the entertainment center which includes TV, receiver, DVD, etc. Only the typical power strip with circuit breaker. (My bad…I know) Although the power strip was unplugged prior to power being restored the sub was still plugged into another outlet. We’ve had power outages in the past with no consequences.

It’s been years since I’ve “tinkered”. I have a Fluke 77 DVM but no other serious troubleshooting equip aside from a Loftech TS-1 sine wave generator and frequency/dB reader.

So far on my end: Amp removed from cabinet. Fuse is good. Powers up. 3 wires on output side of power supply (red-black-red) plugged into main PCB. Blk wire in middle, one red each side. I’m getting 32.3v on both sides.
 
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Old 08-19-18, 11:36 AM
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Don't beat yourself up to bad. Most surge protector strips are 99% hype. I haven't found too much equipment saved by surge strips. You may have lost the neutral to your house when the service was damaged. A surge protector would have done nothing there.

It appears the transformer is ok. Now set your meter to DC and check for voltage on the two big caps.... C121 and C122. Probably +/- 35vDC. If that is there..... go to C117 and C120 to check for the +15vDC and -15vDC supplies.

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Old 08-19-18, 12:38 PM
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C121 and C122 both show +/- 42.7vDC

C117 15.7v
C120 16.2v

Awesome attachment. Sure helped.
 
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Old 08-24-18, 09:58 AM
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PJmax:

This is almost embarrassing....

Took some time going over the amp again when I had time. Can't believe this was missed. First noticed the darkened PCB around Q117. C107 was bent toward the resistor standing on end in front of C129 the first time I looked so the burn wasn't noticed. Got a feeling I might be in over my head with DIY repairs? It's been years since I used my solder sucker.

https://www.doityourself.com/forum/a...1&d=1535129443

https://www.doityourself.com/forum/a...1&d=1535129467

Your thoughts on this appreciated.
 
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Old 09-08-18, 03:32 PM
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PJmax:

Once again, I appreciate your offering to guide me thru a repair on the JBL sub. Seemed too much to troubleshoot not to mention replacing components.

Found a used Sony 10" powered sub locally. Already in the system and working fine.

Have a great one!
 
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Old 09-08-18, 09:51 PM
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Very nice. Happy listening.
 
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