Technics SU V2X loudness button fault

Discussion in 'General Electronics Chat' started by Phil Russell, Dec 21, 2014.

  1. Phil Russell

    Thread Starter New Member

    Dec 21, 2014
    6
    0
    Hi, I hope I can ask this question:
    A Technics SU V2X amp, infrequent use but no crackles etc from volume control. But there is a problem with the Loudness button. In the OFF position (button out) all seems OK. But when I push the button in, to the ON position the volume increases to a deafening, distorted, crackling level such that the immediate reaction is to let the button return to the OFF position again. Volume control at this point is very low.
    Any ideas? Do you think this is curable and is an easy fix for an amateur? I guess I could just continue with the button OFF but I like to know my equipment is working as it should.
    All lights are lit on the front panel as they should.
    All help and advice appreciated.
    Cheers, Phil
     
  2. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    Too simple. Buy a can of contact cleaner and spray everything that moves.
    I'm sure some people here will have opinions about exactly which can of cleaner to buy.
     
  3. Phil Russell

    Thread Starter New Member

    Dec 21, 2014
    6
    0
    Hey ho .... I will give it a go. Maybe I should dust the unit more ...

    I will report back.

    Thanks for advice,
    Cheers, Phil
     
  4. bwilliams60

    Active Member

    Nov 18, 2012
    725
    90
    What exactly is happening to make the crackling sound? I have a Pioneer SX-5 that does the same thing with the volume control and I know how to fix it, just curious....why
     
  5. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    The carbon track wears a bit and the particles take turns being an abrasive and wadding up in places. Then, there is atmospheric oils and dust. The spray cleaner breaks up the wads and rinses them out. When the carbon wears completely through, the cleaner won't fix it.
     
    bwilliams60 likes this.
  6. Phil Russell

    Thread Starter New Member

    Dec 21, 2014
    6
    0
    Done. All squirted as best I could with the top cover and front panel off. It seems to have worked... thank you. No more sudden burst of raucous sound when I push the button in for 'on'. I thought the small circuit board containing the switch may unclip to allow better access to the switch but was not sure so did not tug at it.
    Surprisingly, with it 'on' the volume increases with far more base while maybe intuition would suggest it should decrease. Also, with volume in minimum and loudness 'on' there is still enough volume to listen to the music etc i.e. it is not possible to turn volume off completely at this point ... unless the muting (-20db) button is on. I do not remember using the muting at any point before. As I said, the amp has had little use in recent years.Interestingly I found the original receipt ... it cost me £139 in 1986 from Tot Court Rd. How prices have dropped.

    But thanks for help ..... much appreciated and information filed away.

    Cheers, Phil
     
  7. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    "Loudness" is about compensating for human ears at low volume levels. It's supposed to increase both ends of the spectrum, if I remember correctly. A little extra tweet and a lot extra woof.

    Don't forget to squirt all the holes you plug stuff into, while sticking the plug in and out to wipe the nasties off the contacts. Remember, input and output jacks have moving parts...the plugs.
     
  8. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    Blimey! I'm pretty sure I once manhandled a king-sized mattress down Tottenham Court Rd. in 1989.:)
     
  9. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    Pretty famous place. Tom Riddle bought a diary there.
     
  10. Phil Russell

    Thread Starter New Member

    Dec 21, 2014
    6
    0
    Hello again.
    Sorry, I have another question regarding the Loudness button on this amp.
    I have cleaned everything as advised and there are no more horrific crackles when the loudness button is pressed. But I am not convinced all is well.
    I have always listened with the loudness 'off' at fairly low levels ... maybe the volume control at setting no. 2 or 3. Now, when I push the loudness button in to 'on' there is a great increase in volume ... ok the bass increases markedly but the volume rises dramatically, far too loud for comfortable listening (except if maybe you are a heavy metal fan which I am not) and cannot be reduced to 'zero' by returning the volume control to zero. There is a 'mute' button on the amp which gives -20db and with that 'on' the volume will decrease to zero with the loudness on.

    I cannot remember the amp acting in this way when I previously used the loudness control.
    But: and I do not think I imagined this; after initial cleaning of the loudness button and getting rid of the crackles, the issue was as detailed above but after maybe an hour or two of running (CD and radio input) pushing the loudness button in did not cause a vast increase in volume but acted more as I think I remember it acting. However after switching off and back on again the next day, the high volume issue is back and remains after several hours. Could this be a circuit issue in the loudness circuit? Maybe a dry joint? The loudness circuit seems to be on a separate small board.

    Sorry to be a pain, but I would like to understand what is happening.

    Thanks in advance and Happy Christmas.

    Cheers, Phil
     
  11. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    OK. You tried the simple way. It fixed some of the nasties, it didn't fix some of them. Now you have to dig into the machine and see if something has become unsoldered or loose, whether another blast of cleaner will finally fix the problem, or if there are bad parts in there. My instincts say, "squirt it one more time, then look for a fractured solder joint where the switch connects to its circuit board."
     
  12. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,070
    3,841
    If you rarely used the loudness feature, the electrolytic caps on that board may have crapped out.
     
  13. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    Yeahbut...an intermittent electrolytic? I've never seen one of those.
     
  14. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,070
    3,841
    I was thinking more about the comment that the volume is extraordinarily loud with the loudness button vs how the loudness button was remembered to function when it was new. Which, if coupled with intermittent super loud, would indicate multiple issues.
     
    #12 likes this.
  15. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    I seem to recall fixing a similar unit with the same symptoms. Solution was to replace a bad electrolytic. I will have to dig up my notes.
     
    #12 likes this.
  16. Phil Russell

    Thread Starter New Member

    Dec 21, 2014
    6
    0
    Once again, thanks for the advice. Once Christmas is over and I can have the table again, I will have a look ... nothing to lose really.

    I am not afraid to delve into the inside once I know what to do and am pointed in the right direction ... hence this post. I have looked for a service manual to no avail. I found a reference in a thread elsewhere, tried to download from a free site, and failed miserably. I have the owners manual but there is no circuit diagram there. I found a circuit for the SU V2 but I expect it is a different beasty ... certainly the cabinet looks different. It may give some idea though.

    I am afraid my own circuit tracking and component checking generally ceased when the old 405 line valve TV sets disappeared. Happy memories of using two sets until I finally repaired them ... one for sound and the other for picture. Happy days.

    Cheers, Phil
     
  17. Phil Russell

    Thread Starter New Member

    Dec 21, 2014
    6
    0
    Hello again ... progress to report.
    I delved into the amp a bit further this morning. Not difficult at all except for two stubborn screws that held the volume and loudness circuit boards to the main chassis. The capacitors on the loudness control circuit ... well, they appear very close to the switch on the circuit so I assume they are the ones that could have been faulty ... are not electrolytics but polyester ones: .056 microfarad 50v 10%, brown coloured case.
    I had found a circuit diagram and it confirms this spec. So ... I was now prepared to replace them as they might have been suspect. But I could not find them locally ... the local Maplins do not seem to list the .056 value.
    However, as I resigned myself to a purchase from the web, I thought I would give a thorough clean squirt around with the spray cleaner. I had already examined all the board for suspect joints/cracks and found none. So, with two connector plugs disconnected I liberally sprayed away, plugs, sockets, the loudness switch again, volume circuit etc. All reassembled and tested. No loud increased volume with loudness engaged. Everything seemingly working as it should. Switched the loudness on and off several times: all OK. Let amp run for over an hour: All OK. Switched off, went shopping (compulsory visit with my dear wife) and had coffee. Returned, switched on again and all was still OK. So I can only assume that it was dirt somewhere as originally suspected. If only I had gone the whole hog and stripped the circuit boards out in the first place! But then hindsight is a great thing.
    So ... hopefully the issue is resolved and I thank you all for your input.
    Kind regards and a Happy New Year.

    PS... I have a copy of the Service manual for the SU V2X and can send anyone a copy if they need it .. just contact me.

    Kind reagards, Phil
     
Loading...