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Ashdown Mag 300 evo II problems

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  • #31
    Here is a repost of the above schematic files:
    EVOII.zip

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    • #32
      Thank you Chuck H and Jazz P Bass

      In the meantime asdown sent me the same PDFs. I'm really helped.

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      • #33
        Good day members, I am John from Cape Town South Africa. I recently purchased an Ashdown Mag300 4x10 of which the transformer was dead. The primary coils were burnt. I carefully removed the Mylar tape insulation and the coils. I joined the wires and using heat shrink to insulate the soldering joints. I successfully rewound the primary and secondaries, it tested perfectly with the limiter lamp in place, giving the desired voltages 50-0-50 and 16-0-16. Upon reconnecting with the amp, it played for a while and then suddenly popped the rear fuse. Limiter lamp connected, it stays bright. After checking every single component on the board, everything seems to be fine, but something is causing a dead short. Yesterday I replaced the output transistors, new 4700uf Caps, bridge rectifier, Polyester Caps, new diodes, all small transistors on the input stage, as well as the C4382 and A1668 transistors, together with the 4 big 0.33ohm resistors. I had the lamp connected, swithed on, it came on bright briefly and then slowly dimmed. After a while I placed the head into the cab, connected the speaker, plugged my bass guitar in, it work quite well. The EQ controls were set halfway. A few minutes into play, I heard a buzzing sound, something exploded inside and the amp died. Upon inspection I found resistor R12 470ohm popped as well as the fuse on the right side of the rectifier. This morning I connected it with the lamp again, new fuse, without replacing the resistor, the lamp came on brightly. A few moments later i saw a spark at TR3 A1294, then TR8 A1668 burnt. I am thinking of putting back the old diodes, small transistors and the polyester caps, replace the burnt transistors and resistor and see how it goes. If anyone in this group might have a similar experience, please do assist. I also have another Ashdown Mag300 4x10 that is working perfectly, the PCB's and components are exactly the same. I can't for the life if me get my head around this problem. Please note that I am nowhere close to be an electronic specialist, just a hobbyist who loves taking on new challenges. I am looking forward to the replies. Thank you so much, greetings from a sunny Cape Town, South Africa.

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