Amp problems? Fixable?

[Galant]

Hi Guys,

Don't know if anyone had any insight on to this but I'm struggling to find much input elsewhere online.

I've had recent problems with two bits of gear and I'm trying to figure out if this is something I can troubleshoot and repair myself or not.

I have some limited DIY experience in general soldering and some electronic component replacement - if that's what this requires, and of course I have a multimeter.

Problem 1 - I have a Logic3 i-Station which after moving it, stopped putting out sound. It powers up and i found that it works fine via headphones, but the main speakers don't put out any sound.

Problem 2 - I have an older JVC UX-5000 mini-hifi that has stopped putting sound out to one speaker. I've tested the speakers and cables and both are fine. The speaker cables connect via the usual black/red spring-loaded cable conenctors.

I'm reasonable confident in pulling the machines apart safely enough, but I'd rather have an idea of what I'm looking for before I dive in.

Any ideas?

Thanks!

G.

[peterb]

Hmm, I'd say the power amp has failed on the JVC, not sure about the logic 3 - could be the same thing, or it could be a dodgy contact on the headphone socket - it depends how the headphone output is derived.

As lot of these devices use a monolithic amplifier - in a single chip. If you can identify the chip, and get a replacement, and are confident about unsoldering and soldering, then repair is usually straightforward. If the amp uses discrete output transistors, you will need to remove them and test them, and if one is found faulty, again replace it.

The logic3 istation may just need a bit of careful cleaning round the headphone jack, or again it may be a faulty output amplifier.

Neither are devices I am familiar with - these are just things I'd be considering before pulling them apart.

You may find that the part numbers on the ICs have been removed, some mfrs do this top prevent third party repairs, although sometimes a Google search can help.

[Galant]

Thanks Peter. Just to clarify though - the headphone output works fine. It's the in-built speakers that don't. Or did I read your post wrong?

[peterb]

Depends how the headphones are wired. If they connect instead of the internal speakers, the socket may have contacts that disconnect the speakers. If those contacts are stuck (they are usually simple contacts), the speakers won't work'. However, if the headphone output is taken before the power amp, then the problem lies with the amplifier circuitry.

You are going to have to do some more investigation.