Roland Blues Cube Stage Scematics

[lalunatech]

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.

[vintagekiki]

http://www.blueguitar.org/new/schem/misc_amp/roland_blues_cube30_60.pdf

[lalunatech]

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.

[J M Fahey]

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.

[lalunatech]

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!

[J M Fahey]

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, that´s Bias current.
But in that case I don´t know what´s 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 I´d 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.

[musictronics]

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

[J M Fahey]

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 I´ll then upload here.

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

[lalunatech]

I realise I never posted a conclusion on here for this one. It turned out to be just a blown fuse, one of the round black soldered in types. The power transistors were connected the wrong way round, the PNP where the NPN should be and visa versa. It is possible that that was my fault. No wonder they were conducting heavily all the time.

[sugeda]

https://docdro.id/tXC3f0l

[Jazz P Bass]

Thanks,Sugeda!

[nickb]

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

It looks to me as though holes for the power transistors have been made in the MDF and the transistors are then bolted to a rear metal panel.

[drewl]

Is there a schematic of the power supply?

I didn't see it in the link from sugende.

Looks like a generic smps, but in the event I can't fix it, does anyone know if they are available from Roland?

I'll contact them and see.

Thanks.

[vintagekiki]

Is there a schematic of the power supply?

I didn't see it in the link from sugende.

Page 2, page 19
... supply is prohibited due to copyright restrictions ...
Page 11/ item 36
Power supply is changed as a complete module.
Page 17
Block Diagram

[drewl]

Duh, thanks.

Repaired the supply, bad mosfet.

We'll see if the rest works.

Thanks.