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Help with Quad 306 damage

Discussion in 'd.i.y.' started by ex brickie, Aug 1, 2019.

  1. ex brickie

    ex brickie pfm Member


    I sold a really nice condition Quad 306 power amp, well packed for despatch. The couriers have managed to throw it about so hard that a part has snapped off the circuit board.

    Excuse me but I know nothing about electronics but it is one of four cylindrical parts (blue colour) number 8650 on the top and 4700uf +/-20% 50VDC

    I can’t solder so I’m not risking re-attaching it to a circuit board. I will try to get an estimate for repair so I can make a claim

    However, if there’s anyone out there who wants to offer me a decent price for the power amp and can fix it for themselves, I’ll wrap very carefully and will sell (I don’t need it)

    Is it an easy fix for someone who knows what they are. Doing with a soldering iron? I can send photos if you PM me your email address
  2. Isobarik

    Isobarik pfm Member

    Sounds very much like a Capacitor.
    Someone will no doubt buy it from you who is capable of fixing it.
    I have far too many power amps,but if I hadn't, I would certainly buy it. Just hope it's just the cap that has sustained damage?

    Last edited: Aug 1, 2019
  3. Fatmarley

    Fatmarley pfm Member

    Where abouts are you? Maybe a friendly local diyer could take a look?

    My 306 had a fault when it arrived in the post. One of the transistor legs had a fracture that's more of a design fault than courier. IIRC the circuit board just hangs off the transistor legs, so any jolts puts stress on the legs.
  4. S-Man

    S-Man Kinkless Tetrode Admirer

    Quite astonishing that one of the main smoothing caps could snap off and the mains transformer is still attached!

    Please post some pics.
  5. wow&flutter

    wow&flutter pfm Member

    I agree, physically pretty small caps in the 306. A pic of pcb would be interesting, to see if the pins from the cap are corroded or just snapped off!
    Does the 306 cover slide off like the 34 to reveal the bottom of the pcb, if it does then that should be an easy fix. If you have to lift the pcb to get to the underside of the board it may be a lot more involved!
  6. ex brickie

    ex brickie pfm Member

    Thanks guys. The lid slides off and it is easy to see the PCB board. Nothing corroded - just snapped the the legs are still there

    The component is a reasonable size - close to 50p diameter size (4 of them of which one has come off)

    I'm in Abetystwyth west Wales..... back of beyond!
  7. Tony L

    Tony L Administrator

    If that really is all the damage (i.e. no cracks in the board) it is absurdly easy to fix and could be done by anyone capable of ordering capacitors and basic soldering. The Quad 306 is a beautifully simple design with nothing to adjust in the way of voltage rails or bias. Just throw a new set of caps at it (obviously do all four) and all should be good. If the caps are original they’ll likely need replacement by now anyway, so this can be viewed as nothing beyond routine maintenance. You just need to find caps of the right pin-pitch to fit the board, not too tall for the case (very easy these days) and stick them in the right way round. IIRC Panasonic make some suitable ones.
  8. ex brickie

    ex brickie pfm Member

    To be honest everything looks very clean inside. I must learn how to upload pics and I can post a photo here!
  9. booja30

    booja30 pfm Member

    I just recapped my (new to me) 306 a few months ago. I used Kemet 63V 6800uF (ELG688M063AT4AA) which fit perfectly. The only trouble I had was getting the old caps out because they were pretty securely clipped to the PCB and I didn't want to pull off any traces.

    BTW, here's the before photo of my 306 with the original bulging caps:
    Last edited: Aug 2, 2019
  10. davidsrsb

    davidsrsb pfm Member

    Unless leakage has corroded the pins, the force required to rip the legs off is likely to have done other less obvious damage.
  11. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

  12. davidsrsb

    davidsrsb pfm Member

    I also notice that the PCB is single sided without plated through holes, so dry joints and lifted tracks are all too likely if the amplifier has been dropped hard.
    If there is no other obvious damage, I am thinking that a date code 8650 on the capacitor means that the amplifier was maybe assembled in 1987 and it is quite possible that the 33 year old capacitors have leaked and corroded the pins to the point that a minor bump detached them.
    Isobarik likes this.
  13. a.palfreyman

    a.palfreyman pfm Member

    You should have a good look around the board as any smaller caps and transistors (which stand above the board on their 'legs') will also tend to be bent / lean in one direction if the amp has had a whack. If not then you might just be lucky. Get an old radio or similar (doesn't have to be working) and a soldering iron and have a go. Not difficult to learn. Bear in mind that for 'snap-in' capacitors which have thicker legs you will need an iron of about 50W and a small roll of eutectic (60/40) tin / lead solder. Move back and forth heating each solder point and 'easing out' the capacitor slightly each time. Take your time.
  14. ex brickie

    ex brickie pfm Member

    Hi. I’ve found an enthusiastic buyer now who is handy with a soldering iron. I’m hoping it will prove wonderful in a new home ......

    Thanks to everyone for their advice and help

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