Trio Stereo receiver left channel problem.

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by Supercoley1, May 6, 2018.

  1. Supercoley1

    Supercoley1 New Member

    Messages:
    8
    Hello. I have a Trio KR-3600 stereo receiver that I have had for while now. I haven't used it for a while but I tried using it yesterday and noticed that the left channel was really distorted and it takes much longer to "build" volume than the right side does. All the knobs and terminal connections have been de-oxited and I have done the following trying to get it to work:

    Changed the speakers over - still left channel is distorted.
    Changed to new cables - still the left channel is distorted.
    Connected to speaker B terminals instead of A - still the left channel is distorted.

    I tried the headphones and initially thought that they had a problem too but here's the strange thing. If I leave the speaker selector where it is (i.e. speaker A) then I get the same problem through the headphones however if I put the speakers selector to off or speaker B they are crystal clear and perfect.

    So there must be something to do with the speakers itself causing inteference? The headphone socket is obviously the old type that just comes from the speaker output itself using resistors and it seems to be when selecting the speakers connected that I get the inteference.

    It only happens on the headphones if the speaker selector is pointed to the speakers connected. I have tried the speakers connected to A and B and both work fine with the headphones unless speakers are connected to them.

    I'm a bit stuck on this one. When I say the left channel takes longer to "build" volume I mean that if I turn the unit on the right channel will be at the volume selected within seconds of powering up. The left one can take 10 seconds and fades in. It is quieter than the right channel (about 2/3 of the right channel volume) and sounds like a radio signal with bad reception. The right one is crystal clear.

    I am only using the radio so nothing connected at the moment. I have tried it with the CD connected and the same left channel problem.

    Wondering if it is as simple as a transistor or capacitor. None of them appear to be bulging and there aren;t any leakages visible anywhere.
     

     

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  2. Bob

    Bob AK Subscriber Subscriber

    Messages:
    2,048
    Location:
    West coast
    sounds like you have a problem in the speaker switch, specifically when it's on the A setting.
    (correct? speaker set on B, headphones plugged it, no left channel distortion?)

    find a copy of the serviced manual, look at the speaker selection and the headphone jack,
    if the headphone jack is NOT a separate amp and is a tap across the amp output and is
    clear, then follow the headphone jack/s switching (plugging in interrupts the signal to the
    speaker).

    amp / headphone jack / speaker selector / cable / speaker (based on your paragraph 3)

    change one at a time, forward and back to isolate. include swap speakers once distortion
    is detected.

    based on your input (more will change my opinion/analysis) look carefully into the headphone
    jack. do not use sandpaper. try sheet of paper lightly soaked with cleaner. or get in there
    with a dental flosser/thin-pick. overdoing it can cause loss of contact and no sound.

    this is assuming both channels under some conditions will result in no distortion. therefore
    not an active/passive component, repeatable, but could be a bad solder joint, crimping
    issues, etc
     
    Supercoley1 likes this.
  3. Supercoley1

    Supercoley1 New Member

    Messages:
    8
    Thanks for the quick reply :)

    I may have been a little confusing. The distortion is on whichever speaker terminal I connect the speakers to. So headphones are clear on A if the speakers are connected to B and vice versa. I have tried 2 different sets of speakers and multitudes of different cables.

    I have a schematic but I'm no electrician TBH. The headphone jack does appear to be the usual tap off the main speaker circuit though. Following the wires from the back of the jack along the circuit board they lead to 2 resistors which in turn then lead into the speaker selector switch.

    Pre-empting a future question I left the speakers wires in but disconnected them from the speakers and the headphones are clear no matter where the speaker selector is.

    So then I connected the right channel to the speaker and still the headphones were clear. As soon as the left channel speaker is reconnected to the cable the distortion re-appears on the left channel of the headphones. So it is just when the left speaker is drawing power that the distortion is present on the earphones with the speaker selector in the position of whichever terminals the speakers are attached to.
     
    Last edited: May 6, 2018
  4. Bob

    Bob AK Subscriber Subscriber

    Messages:
    2,048
    Location:
    West coast
    good going on the troubleshooting.

    first off, the two resistors you see are the dropping resistors for the headphones. this is to prevent
    full power going to the headphones and treating your ear drums like Japanese war drums.

    sounds like the headphone jack switch and the speaker switch is OK (assuming both are clear
    through the cables to an unattached speaker on channel A).

    this boils down to something at the speaker end of the cable, and/or the speaker itself. if
    any speaker attached to this cable shows the problem then its less the speaker but still
    a factor.

    if you have a resistor (anywhere from 10- 200 ohms - doesn't matter since you will have
    your headphones plugged in and hopefully LOW volume) then use it in place of the speakers
    to remove the speakers as the culprit.

    (try clipping to end of speaker cable and try it while listening to headphones)

    I suspect your original symptom has something to do with the left channel amp fluctuating
    from normal equivalent operation with the normal right channel.

    it may be the far smaller load (8 ohm headphones plus dropping resistor) does not trigger
    the distortion because it draws less current/power versus the lower load of just the speaker.

    now that I think about this. I suspect it's the left channel amp that needs a close look at.
     
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  5. Supercoley1

    Supercoley1 New Member

    Messages:
    8
    I think I am confusing things. I have 2 different sets of speaker so 4 speakers in all. They all work fine on the right channel connected as speakers A or B. They all give distortion on the left channel on A or B. So it doesn't matter whether I use the A or B terminals to connect speakers to, the left channel gives distortion. And all the speakers are fine connected to right channel. They all give distortion on the left channel. If I were then to assume that the right cable is working because of this and swap them over I still get the same problem.

    The headphones give no distortion unless a speaker is attached to the left channel of the terminals selected by the speaker switch. So I can work around the headphones as I can turn the speaker switch to off or the non connected terminals and the distortion is gone. I'll have a look round for a resistor though and try it. I'm fairly certain it is the amp end rather than speakers. All these speakers work fine on other equipment.

    p.s. These are 600ohm AKG sextett headphones. I'kll try some cheapies see if the same result happens.
     
    Last edited: May 6, 2018
  6. Bob

    Bob AK Subscriber Subscriber

    Messages:
    2,048
    Location:
    West coast
    we are converging. I think it's in the amp - I bet you could trigger the problem, using a pot or
    several resistors: start at high values and go down. at some point the distortion starts. you can
    use headphones to listen in and not have either a cable or a speaker attached.

    In fact, hook up one end of a 8 ohm resistor to one end of the speaker posts then tap
    the other end of the resistor to the other speaker post. should hear it in the headphones
    (no speaker or cables attached to left channel speaker outputs)
     

     

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  7. Supercoley1

    Supercoley1 New Member

    Messages:
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    I'll look for some resistors. Must be some scrap electronic item in this house. lol The distortion isn't a volume thing though. It is present at the lowest volume through the speakers and doesn't increase in the level of distortion. Same amount of distortion to music ratio no matter the volume.
     
  8. Supercoley1

    Supercoley1 New Member

    Messages:
    8
    TBH I am now looking at buying the same amp and then selling this one on for someone else to play with. Reason being I have this in a nice macassar ebony box so I want to keep that and thus need the same amp to fit in the box.

    I have tried a fair few different things. Switching the L/R cables around in the molex? connector and the problem stays with whatever is connected into the left connectors of the molex. i.e. once swapped around and the unit thinking the left molex connectors are the ones connected to the R speaker connections on the back the R speaker has the distortion.

    So the left hand output side inside the amp has the problem. The right side is perfect. I don't really fancy troubleshooting all the caps and transistors through the circuit. The L and R are on the same board at the front of the machine behind the knobs.
     
  9. Bob

    Bob AK Subscriber Subscriber

    Messages:
    2,048
    Location:
    West coast
    your second paragraph: do you mean you swapped the output channel's internal
    connectors and the distortion followed the change?

    probably a lost opportunity since you have fallen in love with this unit. your next one will be
    equally old - 41 YO, and still subject to the winds of age. units of this period will have almost
    mandated a second recap. IOW that next working unit is on borrowed time. and if there's
    a third unit in your future, you may have to circle back.

    it would make better or perfect sense to keep this unit as a spare. ebay shows a parts unit
    sold for less than beer/cigarette money for a short weekend. ($20).

    then slowly work on the unit. the schematic is rather well documented. caps - only four in
    each channel - takes 4 minutes. that's if the only problem is in the left channel output.

    not sure how you came to the conclusion about troubleshooting the caps and transistors.
    may not be that complex. it may not even be that left channel output module. it could be
    earlier in the sound chain eg where the signal enters your unit. we assumed it was the
    speakers based on your initial input. it would be a simple one-minute test to confirm or deny.

    not trying to convince you but this is how I started out many decades ago - no EE degree,
    no internet, no books available at that time (long before barnes and noble, et al), and above
    all no one to ask questions. based on post 1 there's enough other clues to further screen and
    diagnose the problem. with more information it can be analyzed down to a couple simple fixes.
    and if you intend to upgrade gear, then what you learn may be useful in troubleshooting
    future gear even if you don't touch it, you can lower the costs of diagnostics and therefore
    the repair.

    however, it is your decision and not a bad one (not dumping in the landfill), do track the buyer
    he may have it fixed and resold quickly. in fact, you could do a deal...

    good luck
     
  10. Supercoley1

    Supercoley1 New Member

    Messages:
    8
    It's definitely not the speakers themselves as they work on my other amp and my modern AV.

    Yes, when I swapped the L and R wires around in the molex connector inside the distortion moved to the right speaker so it isn't the connectors on the back. The unit was working 2 weeks ago fine and sounding beautiful. I'll think about dabbling but may well keep it as a spare. Looking at past sales "working" units sell between £40 and £60 which isn't a lot really. The only one on ebay at the moment is £105.

    I need to learn how to follow a schematic really before gauging it. To my eyes it is very hard to follow with lines crossing each other all over the place. Would be easier if the did a schematic exactly as you see the board itself so you can reference positions etc.

    I can solder a bit. I need a fine tip replacement but I redid the lamps myself as well as interconnects etc.

    The source I am using is the FM inside the unit. Initially I first heard the distortion the other day when trying to use the CD player in AUX. I initially assumed it was the interconnect cable but then when I tried the FM it had the same distortion.
     
  11. Bob

    Bob AK Subscriber Subscriber

    Messages:
    2,048
    Location:
    West coast
    step by step.

    you might need a ne/refresher course in electronics (hopefully this was taught in the UK
    prematriculation or O/A levels), then reading a schematic, then run through the "stickies"
    here on AK about touching your units, troubleshooting, then deciding on components.

    there are online courses that walk you through reading a schematic
    and there are only a few rules (left to right, component ids, active/passive
    devices, power stuff).

    once you cover the basics, the criss cross lines make sense, connected one use a "dot".
    and you can start by grabbing a service manual and looking at the parts layout which is
    the intermediate view between the schematic and the actual device.

    you could start now, by printing multiple copies of schematics and parts layouts and
    using one copy for caps, then one for resistors, then one for voltages, then
    compare/verify/identify parts from these copies for a BOM and potentially ordering
    parts for a complete rebuild. you will learn a lot. and won't take more than the days
    we've spent on this.

    lastly, any working unit will follow your unit: works one day then it doesn't. they are all
    30-40 years old, in somewhat misleading condition (externally great cosmetics does
    not equal equally excellent working electronics and components will decay over time
    without visible indications), so whatever you learn on this in it applies to that working
    version, and to all possible units you may ever buy in the future regardless of
    country of origin, length of usable service life, and any abuse.
     

     

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  12. Supercoley1

    Supercoley1 New Member

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    Lol. Nope. I remember using a soldering iron either once or twice and a small circuit board marker and acid bath once but I am 43 and remember not a lot from my early school years. This would have been before I was 14 :) I've done lots of soldering since though but I am more a "copy someone else" kind of worker rather than understanding the whole thing.

    It is the schematics that I need to work out. Following the lines from A through to Z and understanding all the points inbetween. Looking at the schematic for this unit it is hard for me to see where L actually goes.

    I get what you are saying though. It is like learning a language (just easier.) Looks like gobbledygook at the moment but learn what it means and it becomes clear :)

    Not sure on the complete rebuild though at the moment. I'll be patient on it. I have a '73 Rotel connected up while this Trio is out of action. Doesn't sound quite as nice but still does the job pretty well.
     

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