Roland Cube 40Xl

[basher106]

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.

Hi thanks for your reply really appreciate it, i have healthy 19.5v on the two vias on the right side of pic F1 F2 fuses but on the left side is 0v on both vias with fuses in place! so no power from the left vias of the fuses f1 f2 !

[basher106]

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

hi thanks for reply just checked all 4 fuse vias test ok, i wouldn't have thought of that thanks.

[basher106]

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?

Hi Nick I removed the tda 2050s yesterday and the f1 f2 fuses all came out nice and clean with a £90 electric desoldering gun from china! very handy, so I still have all the original parts and can refit no probs.

Ps just found with phone magnifier C148 track burnt - side of c135
their right side of C148 is stright to pin 5 of ic17 tda2050 +20v ish so I'd take pthat cap is probably knackered and possibly shorted I've repaired the left side track.

Also yes I do have a scope.

[g1]

Like Helmholtz said, if the fuses are good they must allow the voltages to pass across.
If you still have them removed from circuit, double check them. How many ohms are you reading resistance?

[basher106]

[QUOTE=g1;n918569]Like Helmholtz said, if the fuses are good they must allow the voltages to pass across.
If you still have them removed from circuit, double check them. How many ohms are you reading resistance?[/QU


Hi ohms across fuses are both 0.01 so all good

[The Dude]

Sorry. What you describe is not possible. There is either a connection problem or a measurement error. You can't have voltage on one side of a good fuse and not the other side. It's a piece of wire surrounded by glass.

[g1]

Yep, what he said above ^^^. Have you double checked that your meter is measuring ohms properly?

[basher106]

Sorry. What you describe is not possible. There is either a connection problem or a measurement error. You can't have voltage on one side of a good fuse and not the other side. It's a piece of wire surrounded by glass.

I know, very confusing to me! my new fuses and two output transistors have landed I'll fit just the two new fuses for now and retest, I had my meter set to continuity buzzer test not ohms so i'll stick on ohms and recheck. It's something daft I hope! But I haven't spotted it yet! Will recheck today thanks.

[basher106]

Yep, what he said above ^^^. Have you double checked that your meter is measuring ohms properly?

Gonna recheck my Meter was set to continuity beep test, not ohms, will recheck this morning.

It cycles through continuity / ohms / diode / mode, so a choice of three modes.

[basher106]

Gonna recheck my Meter was set to continuity beep test, not ohms, will recheck this morning.

It cycles through continuity / ohms / diode / mode, so a choice of three modes.

OK my fault sorry!.. the two through hole's left side of fuses F1 F2 are isolated so the 20 v is only on the bottom of the PCB.. Oops, and I now have 20v on pin 5 of ic16 and ic17 both tda2050s (currently removed) ic 17 suspect as had burnt track on c148 which seem ok condition not shorted or open, so I guess I'll fit the replacement ICS and power on I have a light bulb current limiter for first power on.

[basher106]

OK my fault sorry!.. the two through hole's left side of fuses F1 F2 are isolated so the 20 v is only on the bottom of the PCB.. Oops, and I now have 20v on pin 5 of ic16 and ic17 both tda2050s (currently removed) ic 17 suspect as had burnt track on c148 which seem ok condition not shorted or open, so I guess I'll fit the replacement ICS and power on I have a light bulb current limiter for first power on.

New f1 f2 fuses and a pair of Lm1875 output amps fitted powered on but still the same i do have all my rail voltages up now though and -20v +20v to pins 3 and 5 on both lm1875. And no.
overheating burning shorting that I can see. ?

[nickb]

It's a step in the right direction. I couldn't see any electrical connection between the power amp & supplies and the processor so I'm not really surprised that the processor is still dead. So we had fried vias?... That's a worry. I'd expect the fuses to go first. Makes you wonder what went on here.

Anyway, have you tried the factory reset? If that doesn't work you need to take a close look at the processor. That's IC5 on page 20 of the schematic. With a meter and small sharp probes check the power pins for the correct voltages. Don't slip. I see +5, +3.3 and +1.5. (A special thanks here goes to the guy at Roland who chopped the schematic into such small sections you can't see what it going on. Nice one buddy.) Next check the reset line pin goes from low to high on power on with 'scope. Next check the oscillator is running at 16.9MHz on pins 139 & 140. Right after reset you should see activity on pins 79 and 80 ( i.e TP34 /35) as it fetches the code from external memory. If no activity on the data line (pin 80) then the program flash memory IC2 needs checking, but you should check it anyway for power. Also check if anything is running hotter than it should ( I maybe should have said that first).

[g1]

So we had fried vias?... That's a worry. I'd expect the fuses to go first. Makes you wonder what went on here.

No, I think he was trying to measure voltage at top side of the board, but those lands do not connect to the fuses (at least not output side of fuses). So just pilot error, no damage with regard to fuses, which were good all along.

[basher106]

No, I think he was trying to measure voltage at top side of the board, but those lands do not connect to the fuses (at least not output side of fuses). So just pilot error, no damage with regard to fuses, which were good all along.

Yes thats correct sorry about that pilot error on my part the fuse through hole's are isolated to my scratched test points on top side of the board.

[basher106]

It's a step in the right direction. I couldn't see any electrical connection between the power amp & supplies and the processor so I'm not really surprised that the processor is still dead. So we had fried vias?... That's a worry. I'd expect the fuses to go first. Makes you wonder what went on here.

Anyway, have you tried the factory reset? If that doesn't work you need to take a close look at the processor. That's IC5 on page 20 of the schematic. With a meter and small sharp probes check the power pins for the correct voltages. Don't slip. I see +5, +3.3 and +1.5. (A special thanks here goes to the guy at Roland who chopped the schematic into such small sections you can't see what it going on. Nice one buddy.) Next check the reset line pin goes from low to high on power on with 'scope. Next check the oscillator is running at 16.9MHz on pins 139 & 140. Right after reset you should see activity on pins 79 and 80 ( i.e TP34 /35) as it fetches the code from external memory. If no activity on the data line (pin 80) then the program flash memory IC2 needs checking, but you should check it anyway for power. Also check if anything is running hotter than it should ( I maybe should have said that first).

Hi Nick thanks for your help, reply and your time yes I tried a factory reset with a dummy plug shorted mono phono jack and I have tried a behringer ab200 dual footswitch, it's like the amp doesn't initialise properly on.power up.

On.power on All the led lights stay on but I noticed if I turn amp off then back on one light goes out then power off on again, another led goes out in order till no led lights left in order one at a time. Will measure those ic voltages etc and report back thanks again.

Oh and only damage I've found so far! was cap in pic I.posted ic17 has that cap just before its pin 5 20v supply it looked almost shorted right through the track so I changed both ics 16 and 17 and voltages are solid now.