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Thread: Roland Blues Cube Stage Scematics

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    Member lalunatech's Avatar
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    Roland Blues Cube Stage Scematics

    Hiya all
    I have a Roland Blues Cube Stage combo amp in my shop for repair. It is blowing fuses on the high voltage (+/- 43 Volt) supply lines. The power transistors are not blown but seem to be reverse biased. Seems like an unusual design, I can't fathom it out at all. Does anyone here on MEF have a copy of the schematics you could let me have.

    Thanks.
    Dan.

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    Senior Member vintagekiki's Avatar
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    Member lalunatech's Avatar
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    Thanks vintagekiki but I have seen that one but the Blues Cube Stage I have is a little different. The power amp circuit is not the same as the BC60.

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    Old Timer J M Fahey's Avatar
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    The power transistors are not blown but seem to be reverse biased.
    Not sure what you mean by that.

    Are you diode testing them out of circuit?
    Post transistor codes.

    If in circuit: what is Vbe, Vce at each of them?

    What is Voltage relative to ground, no signal applied, at each emitter and collector?

    Are you using a bulb limiter?

    Please post a couple close ups so we have at least a rough idea of what you have.

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    Juan Manuel Fahey

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    Member lalunatech's Avatar
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    Here are some photos.

    The two power transistors are not blown but are both conducting at idle. The drivers are both intact too. It must be a fault earlier in the circuit. If I had the schematic, I could probably track it down. Roland used to be great for support and parts but in the UK they have recently outsourced all their parts supply and servicing. They have turned into an impenetrable citadel!

    Click image for larger version. 

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    Old Timer J M Fahey's Avatar
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    The two power transistors are not blown but are both conducting at idle.
    Not sure what you mean by that.

    * Are they in circuit, powered, and pass a few mA?
    No big deal, thats Bias current.
    But in that case I dont know whats blowing your fuses.

    * are they out of circuit, unpowered, and passing some current they should not, just under multimeter internal battery voltage?
    Then they are lossy or dead.

    So please be a little more detailed.


    As a side note, I found it *weird* that Roland mounts heatsinks straight to a CNC carved MDF piece, WTF?

    Looks like one of those DIY Audio home projects where builders not equipped to work with metal nor inclined to buy a commercial chassis, make an amp chassis out of wood.

    For a home builder working with indequate tools, fine, but for .... Roland?

    As of the amplifier, it looks both very complicated and hard to work with; to boot no service data is being offered .... disposable amp?

    Try to get a service manual from Roland, but if not possible, personally Id send it back and let customer deal with Roland himself.


    Just seeing 1 tube, 10 ICs and 60 transistors , most of them SMT on "just a power amplifier" makes me cringe and label it as disposable.

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    Juan Manuel Fahey

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    I have the Service Manual, but it is too big to upload here (even zipped).
    PM me and I can email it to you.

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    MUSICTRONICS
    Electronics for the Music Industry

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    Old Timer J M Fahey's Avatar
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    Thanks, will do.

    Then will probably "print" it using Cute PDF which allows me to turn it into a few smaller PDF, as small as 1 page each if needed, , which Ill then upload here.

    I am very intrigued about what do so many transistors do.
    Theres even a PCB section with 13 (or was it 16?) SMT transistors in a stamp sized area and practically nothing else WTF?????

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