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QUDOS build disaster

Discussion in 'd.i.y.' started by grahamdocman, Mar 18, 2021.

  1. grahamdocman

    grahamdocman pfm Member

    Ignored my own "safety" rule and finished assembly when tired !
    I inserted an MJ15003 instead of MJ15004 for Tr10 - fried the O/P transistors and the 0R22 2.5W resistors -

    Further proof of tiredness, did exactly the same on the next board !!!!!o_O

    I've checked the R100 resistors (2W) and the 1N4004 diodes (D3,4, 6 &7) and all OK (disconnected one leg on each to test) - all fine

    I've checked R15 8R2 - also fine.

    So it looks like I've got off relatively lightly.
    Easy to find replacement MJ1003's

    QUESTION: I'm struggling to find the 2.5W 0R22 resistors, but plenty of 3w resistors are available. I'm assuming there's no problem in using higher wattage rated resistors - am I correct ?
    Otherwise, anyone know where i can get the 2.5W ones ?
  2. bugbear

    bugbear pfm Member

    I cannot think of any reason why a higher wattage resistor would be a problem.

    But then I don't know very much.

  3. Vinny

    Vinny pfm Member

    So long as higher power resistors, otherwise same type, actually fit, there's no reason not to use them.
  4. a.palfreyman

    a.palfreyman pfm Member

    Many years ago, the guy who trained me on FLTs said, when you make a mistake, you are pretty much guaranteed to make a second one in quick succession because you are thinking about THAT and not what you are doing now. Know what you mean about repeating the same mistake straight afterwards. Almost as though you have GOT to keep going to make up for the blunder and then fall further down the rabbit hole.
  5. grahamdocman

    grahamdocman pfm Member

    Exactly what I did ............. I take consolation in that I'm not alone
  6. Gervais Cote

    Gervais Cote Predator

    Higher wattage is okay as long as resistance remains the same.
  7. Loz828

    Loz828 pfm Member

    No problem using higher wattage resistors as long as they physically fit. Make sure you replace with same type (wire wound in this case I think) and the same or better tolerance.
  8. Pete MB&D

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

    I make emitter resistors from low resistance metal film resistors on a small pcb they sound good and blow very quickly in fault conditions and don’t burn your boards.

  9. Tintinabulum

    Tintinabulum pfm Member

    Where do you think "third time lucky" came from...;)
  10. a.palfreyman

    a.palfreyman pfm Member

    Is that the 0.22R ones? What power rating, 1W? If so, I like that, clever, cheap, easy to spot/replace etc.
  11. Pete MB&D

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

    I use 5 1R 0.6w resistors in parallel which makes a 3watt 0.2R resistor.

    a.palfreyman likes this.
  12. bugbear

    bugbear pfm Member

    I'm starting to see a little parallel o/p transistor sub board design in my head...

    I assume there would be "issues" to be considered with lead length from the HACKERNAP/NCC/NAIM board to such a sub-board?

  13. grahamdocman

    grahamdocman pfm Member

    I stopped, went to bed, had a good nights sleep and woke up thinking "bugger, I know what I've done" !
    Next board = 3rd time lucky

    Literally and metaphorically, I couldn't see it when I was tired

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