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the dreaded Boston acoustic VR2000 sub woofer hum
the dreaded Boston acoustic VR2000 sub woofer hum
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Old 12th March 2015, 09:28 PM   #11
Shadydave is offline Shadydave  United States
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LM78XX and LM79XX regulators like to go into oscillation.
If you put a 10 - 47 mfd electrolytic and a 0.01 mfd Tantalum between output and ground they always calm down.
The Tantalum is important and if oscillation is happening it takes a large electrolytic without the Tantalum.
In my experience.

Best of luck to anyone doing repairs,
Dave
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Old 25th April 2016, 04:07 PM   #12
burmeister is offline burmeister
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Default Boston acoustics v2000 humming

I know this is quiet an old post but I would like to say thanks a lot for your help.....got this sub very cheap and had the same problem.....just followed your advise and it worked out very well.....now, I have dual sub, with paradigm reference sub15.....both bought in Friday market.......






Quote:
Originally Posted by VidTech View Post
I had an issue with my VR2000 sub a few weeks ago. Maybe this will help others with this type of failure.

Symptom:
Amplifier hums when on. Input is irrelevant. Volume control affect hum level slightly.

Diagnosis:
Regulated negative 12 volt supply developed about 1 volt p/p, 60/120 hz sawtooth wave riding on the DC voltage. This power supply is the negative portion of a bipolar supply, which supplies a stable voltage to the filter networks, input buffers, etc. Input and output caps replaced for the negative 12 volt regulator. Measurement of capacitor indicated original main input filter cap(C13) measured 25% lower than design spec.

Repair:
The negative rail is the actual culprit in this case(C13 and C17), but due to the age, the positive side was also replaced(C18 and C19).

Normally the main filter caps are suspect when dealing with long service linear supplies. These were changed as "routine maintenance"; these components have been in service 24/7 for at least 12 years.

Also, under temperature and current extremes, I have seen these regulators get unstable. However, I haven't seen this symptom exhibited. That said, if I would have had one in my parts box, I would have swapped it out while I had the opportunity because of its age.

DIY tip: Use a permanent marker to mark polarity for the caps. Replace the caps with the same polarity. If reversed, they will fail and possibly explode. Also due to the type and design of this power supply a higher value can be used for C13 & C18. I used a 1000 ufd @ 25 volt cap.

Parts List:
C17, C19 - 100 ufd @ 16 vdc radial electrolytic capacitor
C13, C18 - 470ufd to 1000ufd@ 25 volt radial electrolytic capacitor
U2 - LM7912 3 pin negative 12 volt regulator
U3 - LM7812 3 pin positive 12 volt regulator
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Old 2nd July 2016, 01:14 AM   #13
skyhouse71 is offline skyhouse71  United States
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I am having this same problem and have found this thread to be a great help. However, if anyone is still monitoring this thread, how do you get the circuit board out in order to replace the parts? My board is covered with a grey, rubber like cement and I think i may have to take apart the binding posts in order to get the circuit board off but I don't know how to do that. Can anyone help with that?
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Old 2nd July 2016, 10:40 PM   #14
skyhouse71 is offline skyhouse71  United States
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dont know if anyone is reading this but:

I was able to get the board to separate from the rubber cement but now that I can see all the parts, the U2 and U3 on my board are 8 pin op amps JRC 4558DD. How to you replace those with a 3pin voltage regulator? very confused. Unless I have some design that is different.
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Old 3rd July 2016, 08:07 AM   #15
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Obviously you have a different design release. The 4558's are dual pre amps and the 3pin LM's are voltage regulators. Manufacturers as they change factories, change their designs. Have you got a service manual? Is yours Class D with a switch mode power supply?
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Old 3rd July 2016, 02:31 PM   #16
skyhouse71 is offline skyhouse71  United States
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Thanks for the reply. I emailed Boston Acoustics last week for the service manual but they said they don't have any they only gave them to there service techs. So unless you guys know of another place to get them I am SOL. Would there be something on the circuit boards?
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Old 17th November 2017, 04:26 PM   #17
Mad A is offline Mad A
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I have the same sub with the same hum so I will go ahead and try replacing the C13 and C17 capacitors as mentioned earlier, and maybe the other two while I am at it.

I am a complete newbie when it comes to this, but I learn quickly with the help of the internet and youtube videos

Can anyone guide me to a link to the proper capacitors I need to buy? Looking to get the ones mentioned below. I tried searching through some websites and was a bit overwhelmed with the options.

Code:
C17, C19 - 100 ufd @ 16 vdc radial electrolytic capacitor
C13, C18 - 470ufd to 1000ufd@ 25 volt radial electrolytic capacitor
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Old 5th December 2017, 05:36 PM   #18
Absoulution is offline Absoulution  United States
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I am having the same problem with this sub. I removed the sub from the box, trying to remove the amp from the enclosure. I removed the screws from the heat sink, but it's still attached.

I would greatly appreciate any help with getting the sub back in operation. It's a wonderful speaker outside of that annoying buzzing/ humming noise!
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Old 6th December 2017, 01:21 AM   #19
ouimetnick is offline ouimetnick  United States
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Send a message via AIM to ouimetnick the dreaded Boston acoustic VR2000 sub woofer hum
If you are certain that all of the screws are removed, then push it out through the hole in the front (woofer removed)

Be careful as there is a cable, and power cord connecting the control panel to the big amplifier heatsink. The heatsink is also VERY heavy because of the big transformer bolted on. Just be careful that nothing falls out damaging the fragile connections.
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Old 6th December 2017, 02:13 PM   #20
Absoulution is offline Absoulution  United States
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Quote:
Originally Posted by ouimetnick View Post
If you are certain that all of the screws are removed, then push it out through the hole in the front (woofer removed)

Be careful as there is a cable, and power cord connecting the control panel to the big amplifier heatsink. The heatsink is also VERY heavy because of the big transformer bolted on. Just be careful that nothing falls out damaging the fragile connections.
Thank You! Thank You! That did the trick.
Hoping these component's will bring her back.

Parts List:

C17, C19 - 100 ufd @ 16 vdc radial electrolytic capacitor
C13, C18 - 470ufd to 1000ufd@ 25 volt radial electrolytic capacitor
U2 - LM7912 3 pin negative 12 volt regulator
U3 - LM7812 3 pin positive 12 volt regulator
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