Roland Cube 40Xl

[J M Fahey]

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 a same model transformer which say 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 im 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 the back on one light goes out rest still on if i repeat it puts another light out even changing colours on one all in order left to right like an engineer test mode hence my thinking its in mute protect mode. Also i read a post someone said they disconnected the 4pin muliplug 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 theyre anywhere near the same!.

Please Please Please use capitals where needed, punctuation, divide text in phrases with beginning and end, etc.
This is gibberish.

[dmeek]

The manual is too large to post here but here is the power supply and amplifier

[basher106]

Please Please Please use capitals where needed, punctuation, divide text in phrases with beginning and end, etc.
This is gibberish.

Sorry about that!. it was typed on my phone, in a rush, will re-edit original.

[basher106]

The manual is too large to post here but here is the power supply and amplifier

Thanks so much for this.

[DrGonz78]

Hey Dmeek? Just out of curiosity how large is that schematic? The site has up'd the allowable file limit size some time ago.

[dmeek]

You're right, I didn't notice that. It's 8M
CUBE-40XL.pdf

[basher106]

You're right, I didn't notice that. It's 8M
[ATTACH]n915158[/ATTACH]

Thanks so much for this, my first thought of pin 1 on tda2050 being shorted to ground as a fault isn't the case, i looked for that first on the schematic! i'll test for voltages present and report back.

If any knows any key areas to check, or of any known common faults or areas to check that would be great.

[nickb]

As mentioned a while back , a good place to start is to check all the power rails.

Go to page 24 of the service manual and check -V1 and -V2 are approx -20V, V1 and V2 approx +20V, A+8V, A-8V, A+3.3V and D+1.5V.

If all those are good then take a look at pg15 of the SM and try a factory reset. This might restore normal function or it might allow you to put it into test mode and you can run through the various tests to see if anything fails.

I don't see any DC detection on the output so I don't think that there is any kind of protection mode and there is no mention of it in the SM. Next steps will require a scope. Do you have one?

[basher106]

As mentioned a while back , a good place to start is to check all the power rails.

Go to page 24 of the service manual and check -V1 and -V2 are approx -20V, V1 and V2 approx +20V, A+8V, A-8V, A+3.3V and D+1.5V.

If all those are good then take a look at pg15 of the SM and try a factory reset. This might restore normal function or it might allow you to put it into test mode and you can run through the various tests to see if anything fails.

I don't see any DC detection on the output so I don't think that there is any kind of protection mode and there is no mention of it in the SM. Next steps will require a scope. Do you have one?

Hey Nick ok sorry late reply I've just managed to measure a few things

F1 and F2 are blown fuses

+V1 and +V2 are dead after blown fuses F1 and F2 power 18.5v is ok up to F1 and F2

+V1 18.5v good up to fuse F1
-V1 18.5v Good

+V2 18.5v good up to fuse F2
-V2 18.5 v Good

A+8v Good
A- 8v Good

A+ 3.3v Good

D 1.5V Good

[nickb]

F1 & F2 are fuses for IC17 so it's probably blown. These are obsolete so don't be tempted to buy, a probably fake, one off flea-bay. Use an LM1875 instead and fit new fuses. Once that is done you can try and see if it comes up.

[basher106]

[QUOTE=nickb;n918404]F1 & F2 are fuses for IC17 so it's probably blown. These are obsolete so don't be tempted to buy, a probably fake, one off flea-bay. Use an LM1875 instead and fit new fuses. Once that is done you can try and see if it comes up.[/QUOTE

Ok will order IC17 and some fuses thanks I'll post results when parts land and I get them fitted, thanks so much.

[basher106]

Ok i removed and tested F1 F2 fuses with a multimeter and they're ok.

In the photo i get 19v on the right side fuse pcb holes the side near big caps, on the left two pcb holes when fuses are fitted there's no voltage.

That's why i thought fuses F1 F2 had blown!, could it be a short on the tda 2050s if so wouldnt this cause the fuses blow?.

Anyway i've ordered equivalent replacements going to change the pair when they get delivered.

[Helmholtz]

A positive sign of an open fuse is voltage across the fuse in a live circuit.
A good fuse is a short, so no voltage between its ends.

[g1]

Maybe the via's are broken between top side and bottom side of board?

[nickb]

If you want my take on it, if the fuses are OK then there is little point in replacing the power amps. If you ordered some, you might as well keep them as spares

As I cannot see any signal other the the headphone detect going to the processor it should work even without the power amps fitted. Replace at least the fuses, check you have the voltages and proceed with the factory reset. I don't have great hopes that it will solve the issue but it's worth a try.

Do you have a 'scope?