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  1. #1
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    Smoking Kenwood Stereo!!

    Can someone please help me out as my Kenny headunit decided to start smoking last week and I don't mean the Malboro kind!!!

    Basically I have a Kenwood KMD-PS971 minidisc HU (with the dolphin graphic display), and while stationary with engine off, a burning smell developed which was kind of like when your tv or other electronic hifi unit is running very hot! Then smoke started emerging from withing the HU, from the gaps in the front. The HU remained working but I switched off straight away as a precaution! (no Sh#t you're thinking!) [img]/ubbthreads/images/graemlins/shocked.gif[/img]

    Anyway, a day later the stereo returns back to normal operation with other 2 RCA's and amps working fine........BUT on re-connecting my bass box (needed the luggage space), I find that even with the stereo on zero volume the sub is thumping away at a constant rate!! As soon as you turn the stereo on the sub is just thumping loudly!

    I fear something has burnt out and causing the sub to act in this way - possibly the sub RCA from the HU?? Or maybe something inside it has burnt out?? [img]/ubbthreads/images/graemlins/confused.gif[/img] I'm really lost for an explanation and not sure how much it would cost to repair or indeed if it will need to be replaced altogether!!

    HELP PLEASE!! [img]/ubbthreads/images/graemlins/crazy.gif[/img]

    Naresh

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    Re: Smoking Kenwood Stereo!!

    Hi Naresh

    Smoke is not a good thing. So definately the damage is done and something will need to be replaced. (electronic components run on smoke, and once the smoke leaks out they are useless!) The only high power components in the HU are the output transistors on the on board power amp, so normally these will be the only components that can generate visible smoke without blowing the fuses. Are you using any of the onboard amps? or are you running everything via pre-outs to seperate amps. If this is the case then you could have a short on the speaker outs (usually touching bodywork of the car). This would be why the unit appears to be still working. Assuming this, what's driving the sub? Presumably a seperate amp, but what pre-out is it running off? Does the HU have a "sub out" RCA? Can you fade the sub at all? When you say the sub is thumping, do you mean it is operating correctly but just at full volume? You've definately done some damage probably to the internal amp, but it sounds like the pre-out for your sub is stuck at full throttle. Alternatively it could be the wiring at the back of the HU. Have you checked for melted cables? Sorry for all the questions, but you need to narrow it down a bit. Cheers, Andy

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    Re: Smoking Kenwood Stereo!!

    From the description given, I would hazard a guess that you have burnt out an earth track on the pcb to the SUB RCA outputs.As Andy asked, are you running the headunit with RCA outputs only or have you connected anything to the speaker outputs?
    Does the head unit work ok all the time with the sub amp RCAs disconnected?
    It could be that the amp driving the Subs has a poor earth connection and therefore is trying to earth via the RCA earth/shield wire.
    Did you install the equipment yourself and was it all installed at the same time?
    Unfortunately, without seeing the installation it will be very difficult for either Andy or myself to pinpoint the problem but hopefully we have pointed you in the right direction.
    Failing this I would suggest you have the install checked by an Audio specialist.


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    Re: Smoking Kenwood Stereo!!

    Hi Naresh, what you need is a short earth lead, (the fatter the better 30amp or so), with good eyelet connectors on each end, and if you can get a couple of gnarly spikey washers (I'm sure they've got a proper name) which will dig into the metal when you tighten them up. Take the glove box out, so you can see what you're doing, and there are a number of good metal anchor points under there. Use the closest one to the HU. Feed the other end up to the hole in the dash. You should have a solid looking locating bolt at the back of the HU, in the centre, which provides a good solid earthing point, but you might want to turn the unit on, so you can hear the interference, and try different points on the metal chassis of the HU, by just holding the earth to the metal. What I did, cos I was totally fed up with trying different things to no avail, was to make up 3 meaty earth straps, attaching 2 of them to different locations behind the glovebox, and connecting both of them to the last location, and finally one up to the head unit. This was on an OEM HU with OEM wiring looms, and I'd already run seperate RCA leads from the autochanger to the HU. I've never had this sort of problem with Alpine components, or Kenwood. On my set up I've got alpine HU, an Alpine 4 channel amp running all the speakers, (4x90W RMS), and a seperate 300w sub amp. I can only hear very faint engine whine with the HU on max volume playing silence.
    Did this all start when you had the smoke problem? Was it fine before that?

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    Re: Smoking Kenwood Stereo!!

    Hi Andy, I totally agree with you, I can't stand the OEM systems, and you only really appreciate decent sound once you've upgraded the HU and added a couple of amps, especially with a good quality sub!

    Nah I wasn't cranking it up at all, was just sitting at a set of traffic lights with the other half so volume was on the conversational level! [img]/ubbthreads/images/graemlins/smile.gif[/img]

    So you saying you have 1 earth cable attached to the HU with the other 3 ends twined together and attached to a single point?

    If I remember correctly my HU has a threaded M8 bolt hole on the back but not actual screw attached so where would I get one of these from?

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    Re: Smoking Kenwood Stereo!!

    You are obviously not as sad as me, with many jam jars full of "useful" bolts, and bits left over from previous installs. You must have something you can nick a suitable bolt from. I could send you some in the post, but won't get to you until Saturday. B&Q have a good selection, just make sure it isn't too long as it might damage components inside the HU.

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    Re: Smoking Kenwood Stereo!!

    Thanks Andy, yup address is same! And thanks Tek - when checking the RCA earth though, if I find there is some resistance between the HU and a particular RCA - what would that indicate?

    I haven't checked it though, plus I didn't take the HU apart to take a look inside, as its been working fine! Gonna try checking the earths first and take it from there.

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    Re: Smoking Kenwood Stereo!!

    Good point Tek. If there is resistance, it means that a connection within the HU could have burnt out (probably because it was handling the current for one of the amps that wasn't earthed effectively), and the RCA's aren't getting an adequate earth, i.e. the shielding on the cables that protect the line levels from interference, are floating, thus not doing their job. The HU will still work, because it will be getting a weaker earth from the amps, but over such a long line of cable it may have reduced the screening effect. That's the frustrating thing with earth problems, they are not easy to diagnose, all you can do is be thorough with earthing straps. Make sure each amp has a good chunky earth to the chassis of the vehicle (as short in length as possible), with a solid connection at both ends. Try the earthing to the HU that we talked about as the earth connection from the OEM ISO connector is probably via a long length of spindly cable. Remember we are talking about small amounts of resistance being introduced to the earthing to make it ineffective as a screen. Resistance is introduced via long cables, ineffective connections and spindly earth straps. All earth straps should be high ampage (30amp), and as short as possible, to minimise the resistance they introduce, with solid connections, preferably onto an existing bolt into untreated bodywork, which can be tightened up good and tight. Avoid using self tapping screw connections. All you can do is earth everything where possible, there's no logical scientific approach other than that. Let us know how you get on, try not to spend all weekend on it (like I did)! Good Luck

 

 

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