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Model 5 woofers keep blowing


Longplay33
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Brought a nice pair of Model 5s that had just been gone through with new caps, In one of the speakers a woofer stopped working after listening to them at a pleasant high volume. I didn`t hear the woofer stop until turning on my receiver the next day. At that point I noticed the woofer not working and smelled a burning smell coming from it. It was then I read that I should not be using the loudness button when listening to my Sansui 9090db at a high volume. The bad speaker seemed to have froze up. Next I brought a replacement model 5 woofer for it. Once I  replaced the bad speaker I again listened to music all night at a pleasant loud volume but this time I did not have the loudness button on. They sounded amazing. The next morning I turned on the receiver and noticed that both woofer speaker`s were not working and a burnt smell was coming from the recent replaced speaker. The woofer that had a burnt smell coming from it had a burnt spot on it where the wires enter it from the back side.  Any idea`s what is happening here ?

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Welcome Longplay

Your Sansui is 40 years old. I love vintage gear but it's the receiver that's blowing your speakers. Have it thoroughly checked by a competent service technician. If you are anywhere near northern NJ I recommend Bristol Electronics in Ho-Ho-Kus, NJ (a real place :D )

-Kent

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I'm not so sure your receiver is to blame.  It has protection circuitry that prevents excessive DC damage to your speakers.  To verify, disconnect your speakers.  Attach an multimeter to the terminals, turn on the receiver and measure the DC voltage at the speaker terminals.  The voltage should be less that 100mv, the closer to 0mv the better.  If the DC voltage is OK, then one has to suspect the known variable, which is that someone worked on your crossover.  It's possible they screwed it up.

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1 hour ago, alkermes said:

If the DC voltage is OK, then one has to suspect the known variable, which is that someone worked on your crossover.  It's possible they screwed it up.

ooooo! I missed the reworked crossovers part. Of course that IS another possibility. The Model Five crossovers are pretty complex and there is the potential to screw it up.

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Having the receiver gone over is always a good idea but if the Sixes are left unscathed I'm leaning more toward alkeremes's theory which is that the crossover work was done wrong.

-Kent

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  • 1 month later...

Well its taken me awhile to post these new facts...... unfortunately I have found that the klh model six`s woofers have gone out just like the model five`s  too....so I guess pointing to the receiver should be my next step , right?    

Can anyone recommend a competent service technician in the tri county Detroit area ?

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Bummer. Ship it to Tim at Bristol Electronics in Ho-Ho-Kus,NJ. He's the best.

If that's too far check fmtunerinfo.com for "repairs". There is or was a recommended shop in Flint.

Kent

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If you have a multi-meter you could do a check for DC as I mentioned above.

A quick check via Audiokarma and here are some quick picks.  I don't know Michigan, maybe one of these shops is near you, they had some happy customers.

http://www.clearviewelectronics.com/  - Keego Harbor

Mike at Northern TV in Madison Heights. (248) 545-1800

ecotopia in West Bloomfield. www.ecotopiausa.com  "looking at their website, it may seem odd and cheap, but they're pretty legit when it comes to their vintage electronics"

 

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Depending on the reading, It could tell you if something is obviously seriously wrong.  And if it is seriously off, chances are a simple adjustment won't fix it. 

All in all, I think your best bet is to bring it into a shop and have them check it out for you.  It will save you time and effort just to head directly to a the repair shop.  And maybe money too, because if you try to do any work on it and don't know what you are doing, it's likely to make it worse.  I'm going to bet that's what you are thinking anyway.  Let us know how things turn out.  The 9090 is one of the classic receivers of its era, putting some money into will not be wasted.

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On 5/24/2017 at 2:43 PM, alkermes said:

Depending on the reading, It could tell you if something is obviously seriously wrong.  And if it is seriously off, chances are a simple adjustment won't fix it. 

All in all, I think your best bet is to bring it into a shop and have them check it out for you.  It will save you time and effort just to head directly to a the repair shop.  And maybe money too, because if you try to do any work on it and don't know what you are doing, it's likely to make it worse.  I'm going to bet that's what you are thinking anyway.  Let us know how things turn out.  The 9090 is one of the classic receivers of its era, putting some money into will not be wasted.

The receiver is almost certain to be passing too much dc into the output.  The first sign of total destruction is the sweet smell of burning voice-coil wire; next comes the smell of burning pulp in the cone itself.  Distortion does not necessarily follow along with the destruction, but a "frozen" voice coil is next with low output with finally nothing at all.  The receiver needs to have a complete service.  A simple measurement across the output with a voltmeter (in the "DC" mode) will show the offset voltage, even with the volume control all the way to zero.  DC voltage shouldn't be above more than a volt or so; if it's high, you are getting rail voltage in dc right into the speaker's woofer. 

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