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Attempting vintage receiver repair - Please Help!

Discussion in 'Troubleshooting and Repair' started by Icon_xof, Mar 25, 2014.

  1. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Yes, the part with the coloured dots is an inductor. See the "L201" marking on the PCB underneath? "L" means inductor.

    The parts in the other photo are almost certainly inductors too. Check the marking on the PCB. Their values are given in µH so "103" is 10,000 µH or 10 mH. The "J" is a tolerance indication, meaning 5%.

    As for what to replace...

    Electrolytic capacitors, yes I would replace them en masse. They dry out. And there's not a huge number of them in there. As Steve says, use an equal or higher voltage rating. Modern electrolytics will be quite a bit smaller for the same specifications. If you have the option, go for Japanese brands - Nichicon, United Chemi-con (UCC), Rubycon, Panasonic, or a European brand, instead of cheap Chinese brands.

    Other capacitors, probably not, unless there's some visible damage. If you suspect a capacitor, desolder one lead and check it for leakage using a multimeter on resistance range. It should read OL, i.e. open circuit. Also check capacitance if you can borrow a multimeter with that capability.

    Inductors, no. Suitable replacements could be hard to find anyway.

    Transistors... I'd be inclined to replace them all, but that could cause problems for the radio-frequency circuits because various parameters will change. But the transistors on the amplifier board would be fair game. I suggest you wait until we find out what's wrong with it though. If none of the transistors has failed yet, you might be better to let sleeping dogs lie.

    Diodes I would treat the same as transistors. Wait and see whether any of them have failed.

    For the resistors, I'm not sure. Replacing every resistor in the thing would take ages, but those cheap old carbon ones can just fail. You could try to measure them to see how many are out of tolerance, but you can't reliably measure them in-circuit, and removing them is likely to make their resistance change, if not actually break them. So it's tricky.

    You may find that high-value resistors (e.g. 100 kilohms and higher) are all out-of-spec whereas lower-value ones are generally OK, unless they dissipate significant power and get warm.

    I don't have much experience with old carbon resistors and how they fail, but I Googled failure of carbon composition resistors and found this interesting post on a thread at http://www.eham.net/ehamforum/smf/index.php?topic=35646.0:

    That's just one guy's experience though. You can try Googling relevant keywords yourself to see what others say.

    Re wholesale replacement of components, I suggest you tell your friend that it's just a possibility at this stage until we know more about the condition of those resistors and semiconductors.
     
  2. padolo

    padolo

    1
    0
    Jan 5, 2019
    Did you ever get this stereo working? Thanks
     
  3. davenn

    davenn Moderator

    13,262
    1,748
    Sep 5, 2009

    The OP hasn't been seen since april 2014
     
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