Roland Cube 80 XL

[Ianm]

Hi,
Hope someone can point me in the right direction. My Roland Cube 80 XL just started making a high pitched screeching noise all of a sudden. The amp was switched on, but not being used at the time that this started happening. The noise is extremely loud when the volume is turned up, almost unbearable.
I checked all the ground connections, done the factory reset a few times, but to no avail. The noise comes on as soon as the amp is witched on, even without a cable being connected or put into the input socket.
What can this be??

Thanks

[J M Fahey]

Here is the schematic:
https://usermanual.wiki/Collections/...atics.pdf.html
which opens in a browser page, or you can straight download it and see in Adobe Acrobat Reader which has better definition , thereis a direct download button in that page.

From what I see, the same signal drives the power amp, a TDA7293, and the phone amp, a NJM4556 (IC15), so please plug phones in and check whether they *also* have that strong hiss or not.
So we know whether itīs a Preamp or Power Amp problem.

The TDA7293 is on a separate PCB, probably mounted against the back panel o some kind of heat sink, and is connected to the main board through 12 pin connector CN9
With amp OFF, I would pull and reseat it to make sure it makes good contact.

In fact, would do same with all others; one by one so as to avoid errors.

Also suggest scoping speaker out and showing here the whistle waveform.

You also might have lost ground connection at the input jack(s).

Sadly Roland (and many others, but specially Japanese) draw their PDF manuals with VERY thin lines, very small letters, pale colours (light blue, green, etc.) so you *can* read details if you zoom in a lot, but if showing a section they become unreadable.

I selected and copied the section showing power amp and headphone out and best I could get is:

[The Dude]

Agree with Juan. Most of the problems I find with these amps are connection issues. Tighten everything. Clean, lube, reseat all connectors/connections.

[Ianm]

Hi Guys, Thanks for the advice, I am going to try that and hopefully it will work. !!!

[Ianm]

Hi Juan,
I have tried the headphone option, and the noise is just the same through the headphones as it is through the speakers. The 12 pin plug is sitting very tight and seems to be glued down along the back end with a hard white compound. I wiggled and pushed down on it so that should there be a seating problem, it would hopefully connect properly. I pulled out all the other connections, cleaned them all and connected again. The same noise is still happening. It is a high pitched buzz that worsens as one turns the effects knobs as well. Probably have to send it to the Roland agents...?
I also inserted a guitar lead, and seems to be working, (whilst the buzz is on even) - when you insert the one side and touch the plug on the other side, it makes the usual noise.

[J M Fahey]

OK.
Sadly about 40% of that amp is Analog (basic input section around IC6) and Power amps) but 60%: Tone Controls, processing, multieffects, etc. are DSP/Digital and basically beyond us mere mortals.

IC6 drives an AK4556 CODEC and then itīs Digital Country.

Guess even pots are not such but Encooders.

IF Factory Authorized Service is available, by all means use it.

If impossible and amp is to be junked/abandoned, personally I would gut it, keep chassis and power transformer, and build inside a "normal" amplifier, even an 80īs Roland Cube, go figure.

No bells and whistles, but a fine usable repairable amp.

Just thinking aloud, huh?

[Ianm]

Hi Juan,

Thanks I have found an amp technician who can help, Thanks very much for your input!