Roland Blues Cube Stage Scematics

[drewl]

Crap, had the power supply working, sort of.

It would power up after a minute or so, but this morning it was dead as a doornail.

Pretty sure it's the pulse width modulator, but it's an un-marked 7 pin module.

I'll start looking up wtf it could be.

[vintagekiki]

Bad mosfet is not bad for no reason. A faulty fet is a consequence, and the cause has not been found.
In order not to do more damage, I personally think it is cheaper to have the Roland BCB serviced at the factory service.

[drewl]

You don't think an smps can fail on its own?

I have seen the pwm fail on units at work when there was no other problem.

When it was working, the rest of the amp was working fine with nothing getting hot.

[vintagekiki]

The failure is most likely due to some in the supply unit components. Repair does not always refer to the replacement of a defective part. Suplly unit schematics is complex, pwm has settings that require specific instruments, which is why the manufacturer does not provide data for power supply.

Question
When the Roland BCS is disconnected from his the power suplly unit (Page 17 Block Diagram) does the power suplly unit have voltages?

[drewl]

Yes, it still had output voltages when disconnected from the rest of the amp.

[vintagekiki]

Yes, it still had output voltages when disconnected from the rest of the amp.

If there are ± 38V, ± 22V, + 12V on the power supply unit, the probability that the unit is correct.
Worth a try
Connect only cable W18 (connector CN406)
W18 gives voltages ± 15V and + 12V for MAIN BOARD.

Cable W13 (connector CN404) disconnected.
W13 gives a voltage of ± 38V for the AMP BOARD.

Connect Roland BCS line out to the input of some amplifier.
If you hear a guitar on another amp (Roland BCS works as a preamp) it is most likely a power amp board failure.

You did not describe how the malfunction manifests itself.

[drewl]

The high voltage oscillator is dead, before it would take a minute to kick in, making a ticking noise.

The secondary side of the HV trans is all fine.

The damn own chip has no markings on it, so I probably will have to send it back or get another.

[vintagekiki]

... chip has no markings on it ...

On that way manufacturer protects sensitive units from unprofessional intervention.
Like I said just the manufacturer's service support. The service will be performed with original parts and you will receive a warranty on the service.

For service, send the complete Roland BCS