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Amp powers up but just hums

With out a guitar plugged into it it just hums i chkd the power going to speeker wires and its 40 vdc the leds light up finn turning up or down the vol still no change plug a guitar no change plucking strings no sound just huming the amp is a bassman 60 by fender it belongs to a buddy of mine i pulled the pcb and found that where the 2 big caps are there are 2 750 0hm 2watt resistors under them the board is kinda burnd looking but the reverse side shows no broken joints or traces i chked the resistors and they read arround 750 - 753 ohms caps may be bad but im thinking more along the lines of the two diodes could have something to do with it but im not sure

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  • Herbert Sparks
    Herbert Sparks Aug 04, 2009

    i chkd the 2 power trannys in this amp and they chkd out ok even though they chked ok i put 2 more in anyway and still the humming when power is applied to the amp with all pots set to 0 and no guitar hooked up ....any more ideas?



    oh btw the transistors are 2sd1046 i used a digital multimeter set to diode chk and ran the test i tested in circuit and after i removed them

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The output transistors are probably shorted. There should not be any DC voltage going to the speakers. DO NOT run it this way for long or you will damage the voice coils of the speakers. This unit needs service. Expect a parts cost in the $25-$40 range.

Dan

Posted on Jul 25, 2009

Testimonial: "that was the problem its fixed and works great thank you and sorry for the late responce but with work and my electronics hobby no time for anything"

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