Roland Cube 40Xl

[basher106]

Hi, all hope you can help, I have a faulty Roland cube 40xl amp it has no output when I switch on all the led lights come on most times!

I don't have a schematic can't find one but found the same model transformer which says it has 2x 15v ac out and 0v on output it measured ok on the 3 pin multiplug which connects to the mainboard so taking the transformer as good I'm guessing the amp is in a mute or protect mode what would you advise next?.

Also when all LEDs all lit up if I power off switch then back on one light goes out rest still on if I repeat it puts another light out even changing colours on one1 all in order left to right like an engineer test mode hence my thinking it's in mute protect mode.

I read a post were someone said they disconnected the 4pin multiplug centre of the board while powered on then replugged in while still powered on! and it reset a chip and amp came back on normally a bit like a stale laptop bios Cmos reset any help much appreciated or a schematic I have one for the cube 80xl but no idea if they're anywhere near the same!.

[Jon Snell]

Check the ext speaker socket.

[basher106]

hi John here's some pics there's only a headphone out on the back.

[Jon Snell]

The headphone socket will mute the main amplifier on this model. Check the socket. I take it you unplugged the cable on the main board.

[basher106]

Ok john thanks for info i will check out the headphone socket i'm guessing it could be a snapped internal connector or broken contact or tarnished lack of use and needs cleaned, and yes i'm sorry i unplugged the 4 pin cable i've left it off since last night someone posted elsewhere that when amp on unplug then plug back it fired there amp stright back up!! it reset there amp with same fault all the leds light up at power on i'll plug it back in now and check out the headphone jack as you say i couldve checked a few voltages if i had schematic i don't want to start unsoldering stuff if its a dodgy heapdphone jack or stale locked ic which just needs some type of shorted reset i get good voltage to the input of board 15v 0v 15v after looking up the tranformer model outputs on google and the two main biggish filter caps i think! near the power in connector are 50v rated so hopefully a bit safer than on a bigger amp ok thanks again i'll post back any findings

[Jon Snell]

Plugging and unplugging a jack leads will normally clean the contacts.

[basher106]

ok i plugged jack patch lead in lots of times in and out still the same i then checked the jack socket with it still in the board with a multimeter it seems ok (plugging a phono patch cable in headphone jack and one lead of meter on the jack tip and following continuity and then again on jacks barrel and it appears to also be switching between open and closed when i plug then unplug the jack in the headphone out socket as on the bottom drawing of my sketched diagram that's the headphone out jack circled, the jack when plugged in has a good firm click when plugging in and contacts look clean.

[Jazz P Bass]

When dealing with a 'no output' issue it helps to narrow down where the problem is arising.
Preamp or power amp.
And this, only after the power supply voltages are proper & present.
So if the power supply is good, I would suggest that you check if you are getting a signal out of the headphone jacks.

[Jazz P Bass]

What gets plugged into this connector?

[basher106]

Hi sorry late reply ok i plugged headphones in the headphone out socket and the guitar into the input jack there's no sound through head phones but anp doesnt switch on properly i think it might be going straight into protection mode as when i power on every light on amp stays lit where as normal there'd be one or two.

[basher106]

Hi Guys any other suggestions? the psu is ok to the main pcb board but amp is either not completing it's power on properly as most times from power on all the led lights stay on, i'm only guessing amp could be in protect mode if I had a schematic i'd have a chance myself to investigate further but posted on here for any help, I could pull out test the two outputs transistors there's also about 8 of those small round through pcb radial type fuses test ok in board but will no doubt have to test when removed.

[Jazz P Bass]

The output transistors are not shown on the pic that you posted.
What are they?
And can you please answer Post #9.

[basher106]

Hi sorry about the connector it's unused vacant here's a better picture of the board I remember getting 18.6 v on pin 5 of both the tda2050 had a good look today Pin 1 on tda2050 is dead short to ground!... That's the bottom right one near two biggest caps.

That's checking it while still onboard though but surely thats a fault ? pin1 on data sheet says non inverting input !
other voltages I've confirmed having probed around bridge rectifier 2x 18.5v DC & combined voltage of 37vDc.
And two diodes near the big two filter caps and bridge rectifier called
D13 & D15 are both 18.3V DC

And two chokes marked 102 all sides measure same 3.3324v except one near ic13 is 3.433v

I'm thinking unsolder test the tda2050 but also check for short on pin 1 PCB hole when its removed I'll leave amp till reply in case unneccasary as I think it's uses non leaded very high temp solder! But I do have a good high temp auto desoldering gun so It should come out OK.

[DrGonz78]

So the Cube 15XL and the Cube 20x/30x has a TDA2050 output IC. This might help to get a general idea about the 40xl output.

[Jazz P Bass]

Nice catch, Gonz!
They are using not 1 BUT 2 TDA2050 ic's.
Set up in bridge mode.