Roland Cube 60 Keyboard

[LastHeart]

Hey guys, I know it's not strictly a guitar amplifier, but it sounds great as a guitar amp, and I didn't know where else to post it!

I've got a Roland cube 60, one of the old ones, which I gave a little clean and refurbish, and got it working.
Now it works but the two power transistors are running pretty damn hot, I'm not sure exactly how hot because I don't a thermometer available, but they're seriously hot.
The amp is still clean and working like it should, but I'm worried if I was to gig with it or something, it wouldn't be practical because heat like that can't be good for the transistors.

Does anyone have any advice? Or even better does anyone have access to a schematic for the Keyboard cube 60, I can't find one anywhere.

Thanks!

Tom

[J M Fahey]

Are they always too hot without playing or after, say, 1 hour loud playing?
One is a problem, the other is normal.

Post a gut picture, showing power transistors and heatsink.

As of the schematic, I'm quite certain power amp is the same as the G60 and B60 same era, so dig up une of those and post it here.
Compare it to what you have.

Part numbers might not be the same, as in R34 in one might be R42 on the other, but the schematic itself should be about the same.

Keyboard preamp should be very clean and hard to overdrive ... just what the doctor ordered after a nice couple pedals

[Jazz P Bass]

The whole chassis is the heatsink.

60 watt amp?

Yeah, it will get toasty if you play it full bore.

[olddawg]

Check the bias. Add a 120v whisper fan after the power switch. Cheap and easy. Also make sure the used enough heat sink compound. I've seen a few Roland failures because they used little or none of it.

[LastHeart]

Hello guys, thanks for the replies.

It's a strange one to be honest, I haven't started her up for about a week, I just did and the transistors don't seem to be running hot now, although the amp does seem a little noisy.
I can't tell if it's just because it's out of the chassis and maybe picking up some cross talk or if something has happened and once I put it all back together it might be a little cleaner.

There's the guts anyway!
I'll keep you updated, I'm gonna check the bias and see where I am from there.

This is my first time on any sort of forum really, so thanks for replying! I didn't think I'd get any advice from anyone.

[Jazz P Bass]

. Also make sure the used enough heat sink compound. I've seen a few Roland failures because they used little or none of it.

Now that's a real twist.

Usually the assemblers gob on enough to spackle the cracks in your ceiling.

[LastHeart]

Yeah, but to be honest I did have to apply some more to the power trannys, the existing stuff was there but it was quite dry and cracked, didn't look like it was doing a great job.
It's a little strange but they're not running hot anymore, I changed every capacitor in the circuit and it seems to have done something.
There is a 50hz mains hum but I'm pretty sure that's just a grounding issue! I'm trying to fix it now

[Jazz P Bass]

Yeah, cracked & dry is pretty much useless.

You keep saying 'the transistors are running hot'.

Under what conditions? At idle (no signal, power on) or when playing the amp?

[LastHeart]

Ah sorry P Bass, at first they were getting really hot when I powered the amp up, but had no signal going into it.
But I've changed all the capacitors and they seem to be fine now, I've had a signal generator running 50hz through it for half an hour and they're warm, but not overly warm.


There is a 50hz hum that I can't get rid of though..
Everything's definitely grounded, think I'm gonna get the scope out.

[52 Bill]

Is the photo that you posted pre or post repairs?

All of the pc mounting screws are missing and for some reason, the ballast resistors have been encapsulated in silicon sealer.

I've seen that done before when somebody that doesn't own a soldering iron is fixing a broken solder connection.