Violent buzzing from computer speakers

[longtallsally]

Thanks again. I kinda had to figure out the "clipping of the pins" with the bridge rectifier, but thought I must be missing a tool like the mop you described.

I won't be able to get a P/N until I remove it and from there will try some of the sources you mentioned and go from there.

This is great as it is turning out to be quite a tutorial in this stuff for me.

 

[unclejed613]

i just had an item (Boston Acoustics sound bar with wireless sub) come in this week that had a bad buzzing noise when any input was applied to it. turned out the RCA plugs were a press-fit type of plug, meaning all of the parts of the RCA jack block snapped together. the ground shells on the RCA jacks had worked loose and were no longer making contact with the ground rail that went down to the PC board. i snapped them back in using a PC board vise and the sound-bar worked......

 

[tunedwolf]

turned out the RCA plugs were a press-fit type of plug, meaning all of the parts of the RCA jack block snapped together. the ground shells on the RCA jacks had worked loose and were no longer making contact with the ground rail.

Interesting fault, I don't think I have encountered snap together sockets before, but I suppose in today's market place the manufacturers will try anything to save some money. Although in this case, I don't see how it could have been cheaper to do

Well, it can do no harm to do a continuity test, just to be certain it is not a screening problem.


rgds

 

[#1supertech]

longtallsally,

I didn't get to reading all the replies to your post, but one thing that I did see with my "sharp eye" in the 2nd pix you posted (of the PCB solder points underside) was the 4700uf Power Supply filter CAP closest to the back plane. Just follow the Bridge Rectifier's + side down to it. Unless my eyes are deceiving me it appears that this filter CAP got somewhat HOT - as by what looks like to be somewhat freshly melted (shiny) solder.

It also kinda looks like there has been some CAP leakage on the opposite side of that CAP on the PCB as by the brownish color I'm seeing - unless that is just mounting epoxy to keep the CAP from moving? Just guessing there, as I can't see it too clearly as from a bit of Jpeg blurring. The tops of those 2 CAP's look to be OK, as I don't see any bulging or blow out there. I can't tell if any other smaller Electrolytic CAP's are blown out either as by the angles and a bit of blurriness there as well. I would check them all out as well.

If there is a bigger (large sized) SURGE RESISTOR tied to the same PCB point I would definitely measure it as well. Value on it would usually be in the 2 to 10 ohm range and wattage rating somewhere 2 to 4 watts. You need to R&R it to measure it as well as that filter CAP so hopefully you are good with a soldering iron.

If you had an O-scope, and knew how to use one - you could just look at the AC ripple across that filter CAP, and rule it out as being the cause!

Bridge rectifiers rarely go bad unless those bad filter caps cause excessive AC Ripple across them. That or the SURGE resistor goes bad and induces a bad ringing effect in the Power Supply. Then that same PS ringing effect is pretty much felt everywhere in the circuitry seeings it supplies DC power to everything on the PCB.

Did you measure the PS's DC voltage at the Bridge Rectifier + point? I'm just guessing here but I'd say it's either a +12-volt or else +15-volt PS Output. Also - there should be a +5-volt Regulator nearby as well. I don't see it mounted on the main heatsink so my guess is that it's hiding behind those 2 big filter CAPS. If there is no +5-volt Reg on the PCB then the main PS output voltage feeds directly into the Power Amplifier chip itself. If that chip is bad then nothing is going to work, and hence the "buzzing" from the speakers. End of story!

If the PS or +5-volt Regulator are bad you only have 2 options. Repair both yourself and hope for the best. If the Power Amplifier chip is bad then you'd have to try and find a crossover part that would work in its place, as sometimes they are a custom proprietary part and not readily available over the parts counter at a Electronics Store outlet.

I hate to have to tell you this, but just looking at that cheaply made PCB you have there - I can tell these aren't very high end speakers at all - quality wise that is. Between the PCB, its components, and the XFMR there's maybe $20-25 worth of parts tops!

Again - these are just cheaply made speakers (PCB wise anyway) at a ridiculously retailed price of $150, so don't expect too much for the money you over-spent on them! I never would have paid $150 for them myself. $50 maybe? Of course sometimes looks are deceiving instead of even being "everything" - until that is you take them apart and then really see how cheap they are made inside! The guts on yours look identical to the guts that were inside my $20 "cmptr swapmeet special" 3-speaker set that I bought almost 10 years ago.

Nothing much has changed PCB wise at all except for the outside cosmetics on your set there verses my cheaper looking speaker set that I had. That's all - sorry to burst your bubble, but just being painfully honest here. Btw - my speaker set did the very same thing yours did - one day 2 years ago now - for no reason at all.

I checked the PS +12-volt Output and it looked to be within spec. At first I thought it was a bad power XFMR, so I swapped that out next - as I have tons of spare parts lying around from all my cmptr repairs I've made over the last 10 years. People give me unused cmptr stuff all the time to no end. Though that seemed to reduce the loud humming/buzzing slightly - it didn't solve the problem. Turned out to be a bad Power Amp chip after I threw my O-scope on it, and for the $20 I spent on the speaker set I just gutted the Bass for parts - junked the rest of it (just a plastic housing anyway), and kept the 2 Satellites for spares.

There you have the long and short of it -

I did find that if your speakers are less then 2 years old you may a valid warranty issue to pursue!

Here's the Company info below:

Company Information
Level 9 Sound Designs Inc.
201-11782 Hammersmith Way
Richmond, BC Canada V7A 5E3
Tel: 604-504-5286
Toll Free: 877-722-8346

Source: Manufacture loan
MSRP: $149.99
Warranty: 2 year parts and labor

URL: best computer speaker pc monsoon at monsoonaudio.com

Hope the input helped - good news or not so good news?

Best regards,

Frank

 

[unclejed613]

unfortunately, taken apart=voided warranty

 

[#1supertech]

unclejed613,

Warranty part -

I had already realized that "misfortunate" part early on, and though I actually started that prior reply before posting it - I left that Mfr's info part in just so the guy could see the error of his ways in taking the cabinet apart, AND unfortunately not really knowing a thing about electronics repair. That coming after seeing the Bridge Rectifier boo-boo part (pix that is) nullifying the/any warranty at that point.

Hard way to learn Basic Electronics 101 at $149 a pop huh?

It may indeed just turn out to be a simple Audio Cabling RCA plugs (Cables) problem as such - who knows? - I'm not there! I never in my life have seen "snap together RCA plugs" as with the stated posts here, but I guess with the electronics mfg world (CHINA) going to the CHEAP as it were - anything is left to the imagination!

Pretty damn lame if you ask me when you shell out $149+tax on anything electrical/electronic in nature today, and then have a $5 weak link like that of funky cabling! No excuse there at all. Mfr's (foreign and homegrown) that go that super-cheap route should just be banned from ever selling their JUNK in this country, as all it ever produces is just more LANDFILL WASTE here in the USA! Bottom line!

When it comes to cmptr repairs, or any electronics repair for that matter, I always look for the obvious first - loose connectors, and then poor solder joints. On cmptrs the latter is very rare as to the Mobo solder points, as everything today bigger Mobo in nature is flow soldered, and leaves very little to error! Then I work my way through the PS, and finally the rest of the Mobo add-on components. Software glitch being the last pain in the butt issue!

FYI - I've opened many an electronics piece of test equipment, or electronics item in general as it were - just to see what went wrong inside before returning it for exchange or a refund. I've gotten to be an EXPERT at doing it, and so much so that even the best of "Factory trained specialists" can't even tell it was ever opened and closed back up again. Regardless of screw type too! As well as all those QA Inspection seals included.

I think I missed my calling in life - I should have been a SPY! hahahaha

Still waiting to see the final T/S result here….should be interesting to say the least.

Frank

 

[unclejed613]

those cheap RCA jacks seem to have just hit the market this year, and i'm already aware of two manufacturers doing a re-think after seeing a huge amount of failures. if i were an engineer that designed a consumer product, i would want ABSOLUTE control over what components get used in the final product, and the power to fire somebody who makes a substitution on the fab line, especially as costly as this one is turning out to be. i would also do abusive testing of the equipment. worst case scenarios tend to show up the weaknesses of components and construction quickly. worst case scenario testing of consumer audio would include using it in a "semi-pro-audio" role, such as loaning an amplifier to a part-time band for road use (believe me, it does happen quite often, the "enlistment" of home audio equipment as backup road equipment for a band).

i got a receiver in from a retail outlet that had 3 ground shells missing off of one of the jack blocks. at the advice of one of the manufacturer's service support techs, i kept all of the jack blocks off of the board that had to be replaced (the jack blocks are not available even as service parts, if you break and lose ground shells, you shell out for a new board)... now i have a small supply of replacement shells.