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HackerNap failed

Discussion in 'd.i.y.' started by Bemused, Apr 23, 2012.

  1. Bemused

    Bemused What's this all about then?

    Really need your help now guys.

    Vellerman speaker protection operated, 50V DC on HackerNap output.

    Amp is currently discharging and I have to find my old build notes.

    What do I check first?

    Many thanks
    Tony
     
  2. Bemused

    Bemused What's this all about then?

    Just measured the output transistors (MJW21194G) base is short circuit to collector and emitter, collector to emitter short, in fact its now a three terminal piece of wire.

    Oh, perhaps I should mention that I measured with the transistors still in circuit.

    Just tried RS but they don't do MJW21194G, Farnell do but I have to order six of them for nearly £30, ouch
    I think I need to get four to be safe, I already have TR7 (MJE15030) & TR8 (MJE15031) as spares

    Any other UK supply?

    Tony
     
  3. Dik Dolan

    Dik Dolan pfm Member

  4. Bemused

    Bemused What's this all about then?

  5. Dik Dolan

    Dik Dolan pfm Member

    My fault, I didn't read your post properly.

    Hopefully someone will come up with a bit of help, or can add your bits to a larger order.
     
  6. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    Hi, Tony

    I had a problem with my hackernap (self inflicted) and I have some MJE4281 in one now and I can't tell any difference.

    I got them from Onsemi as samples you have the register amd make some stuff up about what you want them for but for about $20 they will senmd you some.

    I have some used MJE3281s you could have for free.

    Or if some one is ordering you could tag on to there order.


    Pete
     
  7. Jo Sharp

    Jo Sharp Pulls on doors marked push

    I would not just rush into replacing the output trannies without investigating why they failed. Did you short the outputs? If not then there could be a fault elsewhere that might repeat the expensive loss of those trannies!!
     
  8. Sparts155

    Sparts155 pfm Member

    Sorry things have gone wrong Tony. Try "Future Electronics", they are usually well priced. Also measure the driver transistors cos they can go too. Good luck!
     
  9. Bemused

    Bemused What's this all about then?

    Thanks Pete, a kind offer but I need to keep to both amps the same, its a sort of obsessive problem I have.

    What I need to do is workout what else I may need in the future and make up the Farnell order that way, unless someone else needs to pigyback or visa versa as you say.

    I was eager to get the amp fixed in order to hear the B4 so initially thought to get the output transistors on the way.

    Had a good slug of wine now though and are chilling back down ;)

    Tony
     
  10. toprepairman

    toprepairman Trade: HiFi repairs and servicing.

    Try CPC.
    They are part of the Farnell group and have many of the same parts, but interestingly often at lower prices and in lower quantities.
    Henry
     
  11. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

  12. Bemused

    Bemused What's this all about then?

    Thanks Jo
    Yes I was rushing to get the transistors on there way but I would not fit them until the nice clever chaps helped me with some more detailed diagnosis.

    I don't actually know when the amp failed, could have been any time over the last eight days since my last session.
    I noticed the failure as a result of plugging in my newly built B4 http://www.pinkfishmedia.net/forum/showthread.php?t=118242

    No shorts applied, just a power down (the amps are always powered up), swap interconnects then power back up.

    Tony
     
  13. Bemused

    Bemused What's this all about then?

    Thanks, just checked Future, it a stock item but current stock is zero.
    Yes there must be a lot to check before powering back up.
     
  14. Bemused

    Bemused What's this all about then?

    Well if you have enough for both amps it sounds better but then I would have to strip the other amp and they are a little tricky in my cases, again I need very long legs to reach the heat sink.

    However the HackerNap is a great amp and its worth a lot more than £30, so I will order some new transistors, do the proper diagnosis and fix it proper.
    Hey might even learn a little along the way.

    Now to your solder, 1.2mm, not 0.75mm?
    email me "tony at eclfirst dot co dot uk" I will pick up email in the morning.

    Many thanks
    Tony
     
  15. Bemused

    Bemused What's this all about then?

    Update

    Board now removed which was quite tricky in my amp.

    Output transistors removed and verified short circuit.

    Output transistor Tr9's emitter resistor R26 holed and open circuit.

    Tr7 driver looks ok

    Tr8 driver is open circuit,
    Tr8 base resistor R19 is open circuit (fried)
    Tr8 collector resistor shows signs of burning

    Looking like I should rebuild the whole output stage, would the main rail capacitors C13 + C14 have been damaged?

    Tony
     
  16. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    Hi, Tony

    Something went big time on that amp!

    Check Tr6 and D3 near Tr8

    I would replace the drivers Tr7+8, do you have a variac to power it up slowly?

    Email sent


    Pete
     
  17. Bemused

    Bemused What's this all about then?

    Yes is went big time, although I heard nothing.
    I originaly assumed it was the introduction of the B4 but not having listened for eight days it probably failed some time before.
    The B4 looks fine, has hardly any dc on its output and there are output caps also.
    The diode D3 measures ok but I am thinking to relace the whole stage to be safe.
    I will look further into the amp over the next day or so.
    Yes a variac is a good idea and I have one.

    Thanks
    Tony
     
  18. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    Looks like the vellerman did its job then!

    Pete
     
  19. Bemused

    Bemused What's this all about then?

    Oh yes,
    Sure glad that went in :D
     
  20. graham-r

    graham-r pfm Member

    Tony

    Just a quick question - how discharged was the amp before you connected the B4 ? It is possible that there was sufficient energy left for the amp to go into oscillation when the inputs were swapped. Some amps (Crimson Elektrik for example) are prone to this - I speak from experience, in my case the Velleman did not save the speaker driver !
     

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