TNC113 went dead. Where to start? - Page 2
Close
Login to Your Account
Page 2 of 2 FirstFirst 12
Results 21 to 35 of 35
  1. #21
    Join Date
    Dec 2005
    Country
    UNITED STATES
    State/Province
    Wisconsin
    Posts
    2,019
    Post Thanks / Like
    Likes (Given)
    506
    Likes (Received)
    692

    Default

    Thinking about it power goes from the plug, to the switch, then the small circuit board, then the fuse and voltage selector switch. So the problem cannot be the small circuit board, it has to be the transformer or downstream rectifiers and regulators. I think I am going to have to disconnect the transformer secondary somehow. If the fuse still blows we know the transformer is bad, if it doesn't we know the problem is downstream in the rectifiers/regulators.

  2. #22
    Join Date
    Jan 2005
    Location
    The Netherlands
    Posts
    6,886
    Post Thanks / Like
    Likes (Given)
    384
    Likes (Received)
    2050

    Default

    For a exchange TNC113 I would get a quote from Singer They provide that service
    Reliable shop with experience shipping

    Peter

  3. #23
    Join Date
    May 2018
    Country
    CANADA
    State/Province
    Quebec
    Posts
    242
    Post Thanks / Like
    Likes (Given)
    243
    Likes (Received)
    77

    Default

    Quote Originally Posted by adh2000 View Post
    Thinking about it power goes from the plug, to the switch, then the small circuit board, then the fuse and voltage selector switch. So the problem cannot be the small circuit board, it has to be the transformer or downstream rectifiers and regulators. I think I am going to have to disconnect the transformer secondary somehow. If the fuse still blows we know the transformer is bad, if it doesn't we know the problem is downstream in the rectifiers/regulators.
    An old trick is to put a incandescent light bulb in series with the line. It's called a dim bulb tester. That way you'll never draw more power than the rating of the bulb. This will save on fuses and stress on various components as you plug in.
    If you know what you're doing, you may be able to isolate the/a fault with the power on through a dim bulb tester.

    Also, before you go disconnecting the trafo, there are simpler things you can do to find the most common faults.

    Assuming you have a DMM, disconnect what you can easily disconnect, then measure the resistance across the various filtering capacitors. Sometimes electrolytic capacitors short, and this is a quick way to find that sort of fault.

    Another common fault is when the bridge rectifiers go bad. You can typically measure the diodes of the bridge rectifier in circuit. Random video from a Google search: .

    Good luck,
    Siggi

  4. #24
    Join Date
    Sep 2011
    Country
    GERMANY
    Posts
    3,750
    Post Thanks / Like
    Likes (Given)
    2533
    Likes (Received)
    1538

    Default

    What siggi said. Small board is a filter that stops digital noose from going back down the power line. Unsolder all xformer secondaries and reattach one at a time. As siggi said, problem is likely a shorted bridge diode or electrolytic or tantalum capacitor.


    Sent from my iPhone using Tapatalk

  5. #25
    Join Date
    Dec 2005
    Country
    UNITED STATES
    State/Province
    Wisconsin
    Posts
    2,019
    Post Thanks / Like
    Likes (Given)
    506
    Likes (Received)
    692

    Default

    One of the electrolytic capacitors is shorted. I have it off the circuit board. Diodes test good. Assuming there is only one problem it looks like I have it. New capacitors are ordered. I assume you will recommend I replace both.


    Sent from my iPhone using Tapatalk

  6. Likes AlfaGTA liked this post
  7. #26
    Join Date
    May 2018
    Country
    CANADA
    State/Province
    Quebec
    Posts
    242
    Post Thanks / Like
    Likes (Given)
    243
    Likes (Received)
    77

    Default

    Quote Originally Posted by adh2000 View Post
    One of the electrolytic capacitors is shorted. I have it off the circuit board. Diodes test good. Assuming there is only one problem it looks like I have it. New capacitors are ordered. I assume you will recommend I replace both.
    Electrolytic capacitors are essentially consumable, they don't necessarily even last on the shelf. If you've gone to the trouble of getting the board out and breaking out the soldering iron, you might as well replace all the capacitors you can get to.

  8. #27
    Join Date
    Dec 2005
    Country
    UNITED STATES
    State/Province
    Wisconsin
    Posts
    2,019
    Post Thanks / Like
    Likes (Given)
    506
    Likes (Received)
    692

    Default

    Replaced the shorted capacitor. Everything looks good but the fuse still blows as soon as power is turned on. Damn.


    Sent from my iPhone using Tapatalk

  9. #28
    Join Date
    May 2018
    Country
    CANADA
    State/Province
    Quebec
    Posts
    242
    Post Thanks / Like
    Likes (Given)
    243
    Likes (Received)
    77

    Default

    Quote Originally Posted by adh2000 View Post
    Replaced the shorted capacitor. Everything looks good but the fuse still blows as soon as power is turned on. Damn.
    Well, that's a shame. Back to the drawing board. Check the resistance across the caps again, as one possibility is that you caused another short during repair (I've done it before, doesn't take but a small blob of solder in the wrong place).
    Any time you blow the fuse, you probably want to test the rectifier diodes again, they're not going to like rectifying into a dead short much.

    I suggest you build a dim bulb tester, as that way you'll limit the potential damage anytime you plug in to test.

  10. #29
    Join Date
    Sep 2011
    Country
    GERMANY
    Posts
    3,750
    Post Thanks / Like
    Likes (Given)
    2533
    Likes (Received)
    1538

    Default

    On my VRZ there are three transformer secondaries, one for regulated 5V, one for unregulated 5V, and one for regulated 12V.

    If your TNC is similar, I would unsolder one end of each of the secondaries, wrapping the loose wire with some electrical tape so it can't short out against the chassis or board (which would do real damage).

    Then I would (by hand) connect each one of the secondaries in turn, and see which one blows the fuse (or lights up the dim bulb, if you use Siggi's approach). This way you can isolate which of the DC voltage supply lines is responsible for the high current draw / short circuit.

  11. #30
    Join Date
    Dec 2005
    Country
    UNITED STATES
    State/Province
    Wisconsin
    Posts
    2,019
    Post Thanks / Like
    Likes (Given)
    506
    Likes (Received)
    692

    Default

    Well, time to order more fuses. The last batch I ordered were fast acting. Maybe I want slo blow? I can't tell from the one that was originally in place. How could I know? Any suggestions?

  12. #31
    Join Date
    Dec 2005
    Country
    UNITED STATES
    State/Province
    Wisconsin
    Posts
    2,019
    Post Thanks / Like
    Likes (Given)
    506
    Likes (Received)
    692

    Default

    I re checked the rectifier diodes they are good. Capacitors are not shorted. Ordered slow blow fuses this time.


    Sent from my iPhone using Tapatalk

  13. #32
    Join Date
    Sep 2011
    Country
    GERMANY
    Posts
    3,750
    Post Thanks / Like
    Likes (Given)
    2533
    Likes (Received)
    1538

    Default

    Quote Originally Posted by adh2000 View Post
    Well, time to order more fuses. The last batch I ordered were fast acting. Maybe I want slo blow? I can't tell from the one that was originally in place. How could I know? Any suggestions?
    If the fuse was the original German one from the time of manufacture, then it should have an F, T, or MT on the fuse.

    F = flink: fast-blow
    T = träge: slow-blow
    MT = mittelträge: in between fast and slow
    Last edited by ballen; 09-08-2021 at 03:38 PM.

  14. #33
    Join Date
    May 2018
    Country
    CANADA
    State/Province
    Quebec
    Posts
    242
    Post Thanks / Like
    Likes (Given)
    243
    Likes (Received)
    77

    Default

    Quote Originally Posted by adh2000 View Post
    I re checked the rectifier diodes they are good. Capacitors are not shorted. Ordered slow blow fuses this time.
    I don't think it'll matter whether you use slow or fast blow fuses.

    The only difference is that a slow blow fuse will take slightly longer to blow, and will stress the downstream components more. Until you've cleared the downstream problem you'll just keep blowing the fuses without learning anything new about the problem.

    Some other ideas to try:
    1. Dim bulb tester.
      Put a 15-25W incandescent bulb in series with the dang thing. All you need is a socket and a bulb and a bit of wire. When you power up, you'll see the bulb either glow dimly or light up hard. If it lights up hard, you'll know that you just saved a fuse, but now you can go measure around with your DMM and see which of the secondaries is the lowest. That's probably where you have your problem.
      Now wait for something to get warm, and if something does get warm, that's probably your problem component.
    2. Variac.
      Power up slowly through a variac, otherwise the same idea as above, only more expensive and riskier.
    3. External power.
      Shunt power from an external power source to the secondary circuits in turn. Ideally you'll use variable, current limited lab supply, but an AA battery or two will work at a pinch. Make sure you get the polarity right, and don't exceed the voltage of the secondary circuit.
      If your power supply pegs out on current, or if your batteries get warm, you've identified the shorted secondary. If a component gets warm downstream, that's going to be your problem component.

  15. Likes ballen liked this post
  16. #34
    Join Date
    Dec 2005
    Country
    UNITED STATES
    State/Province
    Wisconsin
    Posts
    2,019
    Post Thanks / Like
    Likes (Given)
    506
    Likes (Received)
    692

    Default

    Slow blow fuses arrived this morning. Installed one and problem solved. Everything is back together and working great. When I first opened this box I thought there was a very low probability I would be able to solve this problem. Looking back maybe it wasn't so bad. So thanks to you guys and PM for helping. I am so happy.

  17. Likes sigurasg, ballen liked this post
  18. #35
    Join Date
    May 2018
    Country
    CANADA
    State/Province
    Quebec
    Posts
    242
    Post Thanks / Like
    Likes (Given)
    243
    Likes (Received)
    77

    Default

    Quote Originally Posted by adh2000 View Post
    Slow blow fuses arrived this morning. Installed one and problem solved. Everything is back together and working great. When I first opened this box I thought there was a very low probability I would be able to solve this problem. Looking back maybe it wasn't so bad. So thanks to you guys and PM for helping. I am so happy.
    Well then, shows how much I know . Congrats on the fix, glad you got it going.

  19. Likes ballen liked this post

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •