Desperately seeking: Roland Cube 20X Schematic

[Dodger]

I have inherited a lovely little Cube 20X that isn't powering up. I've already done all of the preliminary trouble-shooting to eliminate any of the 3 fuses and anything else obvious, without success. Unfortunately I can't go any further without a schematic diagram.

I'm an experienced, retired electronics technician (military veteran) and now own a computer store/electronics repair business.

I would love to repair this Cube 20X and use it for myself, but in days and days of searching, I've been unable to locate a schematic diagram for the Cube 20X. There are schematics floating around the Internet labeled "Roland Cube 20" but they appear to be significantly different that the circuitry I'm looking at in the 20X. Even the component labeling appears completely different.

Can anyone assist an old soldier in locating a schematic or service manual for a Roland Cube 20X amplifier? Thanks in advance for any assistance anyone might provide.

[J M Fahey]

I think I have the plain Cube 20 somewhere but will check anyway.

In any case, maybe parts labelling is different, just add a 5 cent resistor at the beginning and everything after gets shifted 1 up, but actual schematic should not change that much.

Just in case post a good guts picture.

As Enzo would say, to start measure if your power transformer primary didnīt open, follow both primary ends until they reach the wall plug blades, maybe some connector failed or is simply poorly plugged, no damaged open power switch or fuse holder or mains plug in the path, etc.

The final check is to apply test probes at power plug blades, switch amp on and read primary DC resistance ... everything unplugged of course.

If you have some free time, print the Cube 20 schematic you have and check it part by part with the actual PCB, renaming parts if needed .... I suspect it can not be that different.

EDIT: ouch!!! just checked, itīs a very different amplifier, most certainly Digital preamp and effects, probably ClassD amplifier, and SMT parts, the works.

Not even sure it has a conventional iron transformer supply or an SMPS .

Oh well, in any case post the guts pictures, although I remember seeing a smaller one (8/10W?) and it was impossibly compact and complex.

[Jazz P Bass]

You could always call Roland & ask for a schematic.

I think they have a charge.

[DrGonz78]

Well not powering up could mean a faulty switch or even an open primary on the transformer. I would personally go through all the primary connection points on the amp just to make sure it is not the issue. Did you check continuity through the power cord itself? What resistance readings do you get on the primary winding of the power transformer?

BTW there is one website online that I found on a search that claims to sell the cube 20x service manual. I did not want to link it here since I am unsure of the site's credibility, but it's out there.

[DrGonz78]

Jazz... Don't you have a Cube 15x schematic somewhere? I saw a post on here where you posted it somewhere and the link died in the server failure.

Edit: Oh I was wrong. It was not Jazz who posted it but rather asked that it be posted. Which it was and I thought maybe it is out there downloaded by other members...
http://music-electronics-forum.com/t23174/

Double Edit: (I know... I know...) There is a 15xl schematic on Nick's site. If "xl" is similar to the "x" then it might gives a clue about the power supply section?http://bmamps.com/Schematics/Roland/...e%20Manual.pdf

[Jazz P Bass]

Well here is the 15XL document: Roland-Cube-15xl-service-notes.zip

Not too sure how much help it will be.

The 20XL has onboard FX & spring reverb.

Additionally they have a feature called COSM.
(Composite Object Sound Modeling (COSM) is Roland’s innovative and powerful sound-modeling technology. COSM analyzes the many factors that make up the original sound, such as the electrical and physical characteristics of the original, and then produces a digital model that can reproduce the same sound. In designing the CUBE-XL series, Roland meticulously analyzed and modeled array of world-class amps and effects to bring you the versatile and authentic tone palette that these amps provide.)

[J M Fahey]

Well Iīll be d*mned !!!!
First of all, thanks for posting the schematic

2) Iīm completely surprised: the amp is fully analog (the 20XL might have digital effects and speaker emulators, but yet ....) , the supply is conventional,the power amp is our old friend TDA2050 .

Migh be a SMT built amp anyway, but that can be handled, it only takes a pair of young eyes ..... or strong light and good glasses

In a nutshell, the amp looks repairable ... at least as far as the power supply is concerned

[Dodger]

Well here is the 15XL document: [ATTACH]41443[/ATTACH]

Not too sure how much help it will be.

The 20XL has onboard FX & spring reverb.

Additionally they have a feature called COSM.
(Composite Object Sound Modeling (COSM) is Roland’s innovative and powerful sound-modeling technology. COSM analyzes the many factors that make up the original sound, such as the electrical and physical characteristics of the original, and then produces a digital model that can reproduce the same sound. In designing the CUBE-XL series, Roland meticulously analyzed and modeled array of world-class amps and effects to bring you the versatile and authentic tone palette that these amps provide.)

Thanks for posting the 15XL schematic - Unfortunately it looks significantly different from the 20X as well...

So far I've confirmed the voltage out of the power transformer is fine, there's voltage out to the main bridge rectifier, DC out of the rectifier seems good (but I'm not sure because I don't have a diagram to verify what it's supposed to be...) When powering the amp on, I can hear the initial "pop" of the speaker so the amp is getting voltage, but nothing is lighting up, no audio. I did manage to get a non-adjustable hiss at one point so hopefully it's not a write-off.

I've emailed Roland with the hope they'll have a service manual or schematic. Even if I have to pay a few bucks for it, once I get a schematic, I can't imagine the problem being TOO serious... Thanks again for the help!

[J M Fahey]

Cool.

In any case, and while you wait, thereīs a lot of things you can check without the schematic.

So far I've confirmed the voltage out of the power transformer is fine, there's voltage out to the main bridge rectifier, DC out of the rectifier seems good (but I'm not sure because I don't have a diagram to verify what it's supposed to be...)

Ok, post it anyway
Does it have a chipamp?
The "15" had a TDA2050, which is capable of up to 30W, so they might have used one too.
IF so, the datasheet suggests suitable voltages, yours might match it or not.
In any case, post "the number".

Also post a couple gut pictures, specially some PCB closeup.
Besides showing the presumed chipamp (ot might also have a Class D amp but I doubt it), if it has Op Amps they should have something like +12 to 15V on pin 8 and -12 to 15V on pin 4.
If we have some digital processor (post whatīs on the the label), it might be fed +5V, some need 3.3V
The power Led should have around 2V across it if lit.
And so on and on.

When powering the amp on, I can hear the initial "pop" of the speaker so the amp is getting voltage, but nothing is lighting up, no audio. I did manage to get a non-adjustable hiss at one point so hopefully it's not a write-off.

Well, thatīs encouraging.
It has a CD/MP3 player in, to play along, inject some music there, does it play?

Ok Soldier!!! now you know what to do!!! DO IT !!!!!!




and welcome to the Forum

[Enzo]

I would not be surprised if the schematic had no main rail voltages anyway.. Usually the voltages are either present or not. If you lost a filter cap, one would be much lower than the other and FULL of ripple.

If the amp thumps, the power amp probably works. No lights and no audio sounds to me like you are missing one or both 15v supplies.

[paleeman]

Here it is.

cube-20x_30x.zip

[RuiCosta]

hello I have a Cube 20X with the same symptom. It's from my guitar teacher. He wanted to put a switch on the circuit of the auscutters to disconnect the speaker from the amplifier and when trying to solder the switch had the amplifier turned on the power supply went out of power. He turned off the led and never touched it again!
What could have burned?
If anyone knows, I would be very grateful.

[nickb]

hello I have a Cube 20X with the same symptom. It's from my guitar teacher. He wanted to put a switch on the circuit of the auscutters to disconnect the speaker from the amplifier and when trying to solder the switch had the amplifier turned on the power supply went out of power. He turned off the led and never touched it again!
What could have burned?
If anyone knows, I would be very grateful.

It would be best if you started a new thread for your issue - it will be easier to read and you will get a better response.