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I have a (presumably) very cheap Bush 5.1 home cinema kit that was given to me a couple of years ago. I believe it's a "Pro 300" but can't find any information online (althouhg, see update below).

This is far from a great system but it does the job for occasional films/games for now. However, ever since I received it something strange sometimes happens - there is a noticeable "pop" and it seems like all the treble and >50% of the volume goes through the left speaker. This causes, obviously, a very unbalanced and clipped sound. Once it's happened it generally won't go back until it feels like it (hitting the amp/sub used to work temporarily). Sometimes this doesn't happen for weeks and then it suddenly happens and won't go away for a day or more.

I have already ruled out the speaker: swapping them causes them same effect in the right speaker. I have also ruled out the input: it happens on multiple inputs, and swapping the inputs does NOT cause the effect to swap speakers.

Does this suggest anything obvious to anyone (besides poor build quality)? Can I fix it with a multimeter and soldering iron?

UPDATE:

I've now heard it produce noise when the software power (via remote) is off, and a lot more distortion when the source is power cycled (corrected after another power cycle). It doesn't appear to be grounded. Seems like there is grounding issue or partially failed component, but then I wouldn't know. There are several hacks on the board, and a slightly blackened area - although this seems to be connected properly on my tests so far.

I haven't spotted anything obvious yet, but I'm adding photos of the insides and it seems from them that the model is the same as this Chinese one (from the outside appearance and manufacturer/part number of board). To be honest I can't "read" circuits like I can programs, so I'll probably need a good textbook or some more help.

Photos of amplifier guts

Close-ups of chip and part number

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3 Answers

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I'm no electronics expert, but it does sound like a loose connection or a bit of dry solder. If you are moderately proficient with a soldering iron and multimeter you may well be able to isolate the problem and fix it.

By the sound of it though it may be time to send it to the electronics pile in the sky and consider replacing it. If budget is tight and the speakers are sound, you could simply replace the amplifier with a basic unit. If money is really tight, look at getting an older model from eBay, often you can pick up a bargain as owners look to upgrade to 7., Dolby True HD etc. etc. and offload their older 5.1 models.

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It feels a bit more like static build-up or something, the way it pops in and out. Would the normal route be to trace backwards from the output plug until something doesn't beep? If I bought new, I'd probably look to get HD formats support, maybe 7.x, but thanks for the suggestion. I've only just realised that my receiver (which is much better than the speakers, crazy I know) can power the speakers directly if I cut the plugs off, and pre-out to the sub (hopefully). Probably better sound too! But I also like fixing things... – Sam Brightman Jan 22 at 12:02
it could be static, do you have earthed plugs in Switzerland? That could explain it if the earth connection is loose. Like I say I'm no expert, I know just enough to know I shouldn't attempt these things. – vls Jan 22 at 12:21
We do but it's an British-bought system, so it has a three-pin British plug. Not sure if earth is actually attached, or if I've maintained the earth connection through the adapter and extension. However, it was originally a problem in the UK plugged directly into the wall. – Sam Brightman Jan 22 at 12:28
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If you have a problem like this, it's worth noting the Audyssey MultEQ does a surprisingly excellent job of correcting for it (suggesting that it's a crossover/balance type issue in the amp, I guess). Of course, if it keeps going wrong/right alternately it's still a pain.

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This is what I do when trying to figure out problems with electronics.

Look for:

  • cold solder joints
  • charred areas
  • bulging capacitors
  • corrosion

If it's one of them great, now you know where a problem area is. There might still be other problems though.

After you have repaired or replace any visibly damaged parts, and it still doesn't work. I would start pulling simple parts off of it to start testing.

  • diodes
  • capacitors
  • transistors

If after all of that you still don't have it solved, you should probably give up trying to fix it yourself.

You might consider taking it to a friend who knows a lot about electronics. Although I would assume that you would have already done that, if it was a possibility.

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