1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

VU meter not working. Dynacord Echocord Super 76

Discussion in 'General Electronics Chat' started by Rorut, Mar 2, 2018.

  1. JimB

    JimB Super Moderator Most Helpful Member

    Joined:
    Sep 11, 2004
    Messages:
    6,696
    Likes:
    649
    Location:
    Peterhead, Scotland
    ONLINE
    Yes

    Yes

    JimB
     
    • Like Like x 1
  2. Rorut

    Rorut Member

    Joined:
    Apr 27, 2016
    Messages:
    252
    Likes:
    0
    Any easy way to get that old one out from this side? Dont want to damage any copper path
     
  3. Rorut

    Rorut Member

    Joined:
    Apr 27, 2016
    Messages:
    252
    Likes:
    0
    What would do as a replacement?
     
  4. dave miyares

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    2
    Likes:
    -10
  5. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,730
    Likes:
    1,277
    Location:
    Cardiff, Wales
    A BC547 is rated for 45V so should do as a replacement.
    Snipping the legs of the old T200 might be easier than de-soldering and would not risk copper track damage.
     
    • Like Like x 1
  6. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,730
    Likes:
    1,277
    Location:
    Cardiff, Wales
    R206 has R202, 207, 209 in parallel with it, so 50k is a reasonable measurement.
     
    • Like Like x 1
  7. Rorut

    Rorut Member

    Joined:
    Apr 27, 2016
    Messages:
    252
    Likes:
    0
    There is a BC547B and a BC547C
    Whats the difference between ”B” and ”C”.
    I think I have a ”B” somewhere.
    B0E9A0E3-2817-489D-9C05-8486023D0551.jpeg
     
  8. dave miyares

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    2
    Likes:
    -10
  9. Les Jones

    Les Jones Well-Known Member

    Joined:
    May 15, 2015
    Messages:
    1,592
    Likes:
    202
    Location:
    Lancashire UK
    The suffix letter specifies the range of hfe values. If you are using the data sheet from Philips the information is on page 3.

    Les.
     
  10. Rorut

    Rorut Member

    Joined:
    Apr 27, 2016
    Messages:
    252
    Likes:
    0
    Thanks. Would the BC547B that have some difference in Hfe max work for me?

    BC237B
    Hfe min = 200
    Hfe typical = 290
    Hfe max = 460

    BC547B
    Hfe min = 200
    Hfe max = 450
     
  11. Les Jones

    Les Jones Well-Known Member

    Joined:
    May 15, 2015
    Messages:
    1,592
    Likes:
    202
    Location:
    Lancashire UK
    The BC547B should work.

    Edit. Don't forget that if you solder the transistor to the etch side of the board that the position of the emitter and collector pads will be the mirror image of when viewed from the component side.

    Les.
     
    Last edited: Mar 6, 2018
    • Thanks Thanks x 1
  12. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,730
    Likes:
    1,277
    Location:
    Cardiff, Wales
    In this circuit the hfe is not critical.
     
    • Like Like x 1
  13. Rorut

    Rorut Member

    Joined:
    Apr 27, 2016
    Messages:
    252
    Likes:
    0
    Ok have it apart now and desoldered transistor. Seem like it is a different model than whats in the schematic. BC107B

    Can I still replace it with my BC547B?
     

    Attached Files:

  14. Les Jones

    Les Jones Well-Known Member

    Joined:
    May 15, 2015
    Messages:
    1,592
    Likes:
    202
    Location:
    Lancashire UK
    Compare the information in the datasheets for both devices. If you trace the schematic of that area of the board and it matches the schematic thet you posted then almost any small signal silicon NPN transistor should work. You should be able to find the data sheets using Google or any other search engine.

    Les.
     
    • Like Like x 1
  15. JimB

    JimB Super Moderator Most Helpful Member

    Joined:
    Sep 11, 2004
    Messages:
    6,696
    Likes:
    649
    Location:
    Peterhead, Scotland
    ONLINE
    Yes.

    JimB
     
    • Like Like x 1
  16. Rorut

    Rorut Member

    Joined:
    Apr 27, 2016
    Messages:
    252
    Likes:
    0
    I found a 107 and replaced the old one. Now the VU meter works perfectly. Thanks a lot all of you!
     
  17. JimB

    JimB Super Moderator Most Helpful Member

    Joined:
    Sep 11, 2004
    Messages:
    6,696
    Likes:
    649
    Location:
    Peterhead, Scotland
    ONLINE
    A success story - I love it!

    JimB
     
    • Thanks Thanks x 1
  18. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,730
    Likes:
    1,277
    Location:
    Cardiff, Wales
    Good to hear.
     
    • Thanks Thanks x 1
  19. schmitt trigger

    schmitt trigger Well-Known Member

    Joined:
    May 24, 2009
    Messages:
    1,075
    Likes:
    99
    Good for you!

    Earlier type of transistors sometimes suffered from bonding wire unreliability, as others have mentioned. With the actual current and voltage levels it is unlikely that an electrical over stress damaged it.
     
    • Like Like x 1
  20. Rorut

    Rorut Member

    Joined:
    Apr 27, 2016
    Messages:
    252
    Likes:
    0
    Yes really appreciate it. Thanks!
    Another question related to the machine. Im not sure if this is in my imagination but using it for a couple of hours it feels like sound gets a bit distorted. I have not change the tape loop and don’t know the age of that. Any ideas on this? Can old caps affect sound quality?
     
  21. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,730
    Likes:
    1,277
    Location:
    Cardiff, Wales
    Certainly old caps can affect sound quality, if they are in some frequency-sensitive part of the circuit. Their values and ESR can change with age. Electrolytics are the type most prone to cause problems as they age.
     
  22. Rorut

    Rorut Member

    Joined:
    Apr 27, 2016
    Messages:
    252
    Likes:
    0
    Some people say let it be if it works, other places I read replace all electrolytic caps. Would like to put in high quality caps if I do it . What do you think? :)
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice