Question about common symptom in repaired subwoofers

[Chadwide]

Hello all, I've been repairing subwoofers as a hobby with some success, primarily just re-capping them and replacing any visibly bad components. Several of the units I've repaired exhibit the same symptom post repair, and I'm hoping that someone can give me an idea where to start looking to address it. The subwoofers will play distorted audio at low volume, which sounds almost like creaking or scrapping for 1-2 seconds after coming on, and then will operate normally, even under high output. This must be fairly common as I have three subwoofers doing it. Can anyone point me in the right direction?

[jiroy]

Re: Question about common symptom in repaired subwoofers

One of the most problems with subwoofers and other electronic devices as well is good wiring , starting connectors of reputable manufacturers and fresh good copper , which tend to rust and deteriorate with time , making a somehow unwanted resistance . Connectors gold plated ain't cheap but worth the price , and usually people run for cheap things unfortunately . Last week , a client brought me a set , complaining from annoying popping randomly . Soon I discovered that the electric wire was almost cut . Changing the wire ended the problem .
In Another case , I found out that a client using not less than 5 different devices on one outlet , it was a scary thing to see ..
If you have an air-condition , always put electronic devices away from its direct ventilation . Also , interference from other electric devices might cause distortion and other undesired effects ..

[tibimakai]

Re: Question about common symptom in repaired subwoofers

I also repaired a blown speaker on a 10" Klipsch sub(tinsel wires were open circuit). Replaced the wires and it is working great, but every time I give it power, it pops. What can be that as well?
You may still have some bad components in there.
When I have fixed some Onkyo receivers, if I have missed a component, it had distorted sound. Usually I go over and check all the amp components.

[nobbnobb1]

Re: Question about common symptom in repaired subwoofers

I've also enjoyed repairing subwoofers. Some very common problems I've encountered:
1. Bad caps
2. Yellow glue that turns corrosive brown over time and heat

Also interesting to note that many manufacturers use the BASH amp design and in many cases, a bad capacitor is what goes wrong on these. Across different manufacturers with the BASH design, it would seem that components may even be interchangeable between circuit boards.

[Chadwide]

Re: Question about common symptom in repaired subwoofers

Thanks nobbnobb1. I'm aware of the conductive glue issue. Right now I'm leaning towards my issues being related to some of the smaller transistors in these subwoofer amps, perhaps in the preamp section??

[nobbnobb1]

Re: Question about common symptom in repaired subwoofers

Thanks nobbnobb1. I'm aware of the conductive glue issue. Right now I'm leaning towards my issues being related to some of the smaller transistors in these subwoofer amps, perhaps in the preamp section??

I'm still a super beginner but it's hard to say. With capacitors, I've had units that looked perfectly normal with no bulges/leaks and yet it was still bad enough to prevent the amp from functioning. The capacitors that are most likely to fail seem to be the large ones on the power supply, and any unit near heat sinks or other heat sources. Always good practice when replacing caps to try to bend/point them away from nearby heat sources if possible.

After that, definitely test each diode/transistor as those can fail too. But those usually either work or they don't...I've never seen one partially failing to the point where it might cause distortion or whatnot.

Out of all pieces of audio equipment, subs are the hardest on electronics since they are literally being pounded non stop. So always inspect for mechanical damage like cracking solder joints.