Technics SU-3500 repair and full restoration

Discussion in 'Solid State' started by Bert 1100, Mar 29, 2017.

  1. Robert2017

    Robert2017 Active Member

    Messages:
    186
    Hi
    I also have a SU-3500 that I want to mod .
    I noticed that in the original design 8 electrolytics are non polar 6 of 0,47uf and 2 of 47 uf .
    I don't understand why you replace some small value polar ones with film .
    For example you replaced the 0,68 polar with film ....
    Technics already used 8 non polar electros... so I don't understand the benefit of replacing polar small values with film by working against the original design
    I don't want to damage this amp ...
    Thanks
     

     

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  2. Bert 1100

    Bert 1100 Super Member

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    1,176
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    @Robert2017 I thought I had replied to your questions a few days ago....strange.
    Anyway, film caps are in all aspects better than electrolytics, that's why it's good to use them where possible.
    The limits are of course due to size...and cost !
    You won't damage your amp by replacing polar electrolytics by film caps of the proper ratings.
    You can replace polar electrolytics by non polar films.
    You can replace non polar electrolytics by non polar films.
    You cannot replace non-polar electrolytics by polar electrolytics.
    Good luck !
     
  3. Robert2017

    Robert2017 Active Member

    Messages:
    186
    That's great .
    I was just thinking that it is not allowed to replace polar electrolytics by non polar films because I read this on a thread .

    They claimed you can replace only polar electrolytics by polar electrolytics and that only non polar electrolytics can be replaced by non polar films.

    Thsy claimed that indeed there are some situations when polar electrolytics can be replaced by non polar films because the scheme allows that in that particular situation .

    For example this amp uses 2 10000uf polar caps for the psu .

    I already placed the caps backwards and I damaged the amp . I was misleaded by the original caps marks regarding the positive and negative .

    I presume that the same damage would happen if I replaced those with some 10000uf non polar ones.

    I already ordered 2 new caps , a rectfier and a new relay . I hope those 3 will fix the amp .
     
  4. slimecity

    slimecity Super Member

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    3,242
    Location:
    New Zealand
    Lovely modular design in this amp - I love working on technics gear.
     
  5. Bert 1100

    Bert 1100 Super Member

    Messages:
    1,176
    Location:
    Planquiri, Switzerland
    Non polar means that it does not have a polarity, so it accepts voltages from minus the rated voltage to plus the rated voltage, there is no wrong way round for non polar caps.
    Now, try and find a 10000 uF non polar cap :D
     
  6. Robert2017

    Robert2017 Active Member

    Messages:
    186
    But if I put two 5000uf in opposite directions to each other this will result a 10000 uf non polar and if I replace that with the normal 10000uf polar ones the damage will be done because some current will go backwards.
     

     

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  7. Bert 1100

    Bert 1100 Super Member

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    1,176
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    Hmmm...and if you put transistors in parallel instead of the 10000 uF caps it will also be damaged :naughty:
    Just use 10000uf electrolytics of your choice and install them properly and it will work !

    As I mentioned if a cap is NON polar it means it will accept any polarity you give it and give that same polarity back while discharging...
    Now it is nonsense to try or make a 10000uf non polar cap, and I'm not sure using 2 5000uf polar caps can make a 10k non polar....
     
  8. Robert2017

    Robert2017 Active Member

    Messages:
    186
    Regarding your statement that:
    "You won't damage your amp by replacing polar electrolytics by film caps of the proper ratings.
    You can replace polar electrolytics by non polar films."

    I'm not so sure about that . If this is the case means the original amp should have non polar electrolytics instead of polar ones .

    But usually they have a few non polar electrolytics and the rest are polar .

    When I restored the amp I placed the 10000uf caps backwards .

    The original caps are tricky in showing where the negative and positive is .
     
  9. Bert 1100

    Bert 1100 Super Member

    Messages:
    1,176
    Location:
    Planquiri, Switzerland
    The fact that you can does not mean that you should...
    The P.S. caps see only one polarity, always. So it's perfectly fine and normal to use a normal polar electrolytic.
    Non polar electrolytics have worse properties than polar ones and are more expensive, so why use them where they are not needed ?

    So the basics is : film caps are better than electrolytic caps, so you can and should change the small value electrolytics (polar and non-polar, up to 1 or 2.2 uf) by film caps, since they will be small and still reasonably cheap, and can improve the sound.
    For all the rest, replace polar electrolytics with the same, you can go up in voltage rating a bit to be on the safe side. And replace non-polar electrolytics by the same, again you can go up a bit in the voltage rating.
     
  10. Robert2017

    Robert2017 Active Member

    Messages:
    186
    This sounds great .
    When you replaced the old caps you also cleaned the board ?.
    I noticed an oily like fish smell substance under the old caps .
    I hope will not become conductive or something .
    And I forgot to clean the board when I replaced the caps .
    Do you have any idea if the board can be cleaned without removing the new caps ?.
    Some spray or something ?
    If I will be able to repair the amp I will start this experiment replacing polar and non-polar, up to 1 or 2.2 uf with film .
    I will start replacing the recifier , relay and main caps to see if the amp will be fixed ,
     
  11. Bert 1100

    Bert 1100 Super Member

    Messages:
    1,176
    Location:
    Planquiri, Switzerland
    My amp was not very dirty, so the only cleaning that I did was with compressed air and a brush.
    Smells can be a real pain and for me are often the reason why I end up selling things...
    Some amps I have taken out the transformer and given a full bath with soap and hot water, then alcohol to wash out the old flux, then soap and hot water again. Then compressed air to blow out any water from the pots and other corners, then a few days out in the sun. Then only the rebuild begins.
    So, plenty of time from the bath until switch-on...
    Things not to soak : transformers, relays, inductors (many of them in a receiver...) and any other component that will soak up moisture inside, like meters and such...

    Some of the glues used to fix the big caps in place can become conductive and should be removed.
    This is done by first removing the old cap, then soak that part of the PCB with acetone, that soften the glue enough for it to be removed.

    But first things first, get the amp working...good luck.
     

     

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