Roland cube 60 keyboard help!

[pontiacpete]

There doesn't seem to be a schematic that matches this cube. I attached the one that is closest, but the output transistors on the one here are not the same. The one I have here uses 2SC2773 and 2SA1169. The circuit doesn't match up at all. There are 2 fused resistors 10R and 100R on each of the outputs transistors. The drivers are also different.
Does anyone have a schematic that reflects what I'm trying describe?

[J M Fahey]

It seems only you can see it, all I can get is the dreaded clear.gif .
Please zip it or something and reupload.

But in any case, manufacurers use the "transisteur du jour", whateverīs available at good price and meets specs, transistor substitution is incredibly flexible, I wouldnīt worry much about that.

And exchanging fusistors for normal resistors is also possible, as long as ohmic values are close..

Now if circuit has different "architecture" , well, NOW we have a difference.

Check other old Cubes, I bet Bass and KB used the same, and Guitar ones not that different.

Old ones didnīt even use mixed feedback on Guitar, go figure.

[nosaj]

There doesn't seem to be a schematic that matches this cube. I attached the one that is closest, but the output transistors on the one here are not the same. The one I have here uses 2SC2773 and 2SA1169. The circuit doesn't match up at all. There are 2 fused resistors 10R and 100R on each of the outputs transistors. The drivers are also different.
Does anyone have a schematic that reflects what I'm trying describe?

The one called scb-100 in this service manual uses the 2sc2773 in the outputs. What are you trying to fix?

nosaj
https://elektrotanya.com/roland_supe.../download.html

[DrGonz78]

Well it must be that the Cube 60 version you posted is for guitar and not the keyboard version of the schematic. I found a Cube 100 keyboard schematic with the correct output transistors attached. Will keep an eye out for the 60 version but could not locate it. Also, your link is not working...

[pontiacpete]

Also, your link is not working...

Geez... when will I get it right?

Thanks DrGonz. It looks like the CK-100 schematic is the closest to what's here, but it's not exact.

This amp came to me and I found that one of the .33 5w resistor legs broken off the board. I attached it back in place and it was up and running and sent back to the customer. Then it failed again.
This time the 2 fusible resistors, a 10R and a 100R on the PNP side of the output had opened up and the driver(?) transistor B647 had a short and the A1169 appeared to be damaged according to my transistor tester.
I replaced both outputs. For the A1169 I used an A1216. It appears to be a good replacement.
Problem that remains is no sound.

[J M Fahey]

Problem that remains is no sound.

That a very generic symptom, like telling your Doctor "I have a headache, what could it be?", with 1000 possible causes, you must narrow down it a bit.
Measure rail voltage (around +/-40V reaches power transistors and the rest of the power amp.
In your pictures power transistor legs look poorly (cold) soldered to wires, donīt look Factory by any means.
Are wires where they belong?
Since they are floating, not on a PCB or connector, they might have been misplaced.
Measure Vbe at power transistors, you should have some 0.5VDC
Measure Vce, you should have some 40VDC , positive or negative .

This "should" be about same power amp:


Starting from the output: does the speaker work?
Disconnect it from amp and touch it with a battery, does it click/pop?
I thought so, but we must start with something.

Reconnect and turn amp on: any īpop/click/thump at turn on?

Hear *anything* (hiss/hum) with your ear against the cone?

Measure DC at main speaker rail out at the PCB, you will have at least a few mV offset.
Then measure across speaker terminals, do you get same?

If not, amp off, check continuity between PCB speaker rail out and speaker hot terminal.
IF you have a crossover there, treat crossover input as speaker input.

Amp off for a few minutes, measure continuity between PCB speaker out and speaker (or woofer) hot terminals.
You shoud have less than 1 ohm, even if going through a crossover coil.

measure continuity from speaker "-" terminal to ground.

Find the power amp input.
In this schematic,(B60) which I think must be close to yours, it would be Q4 base, in above linked CK100 it would be Q10 base, in any case the first transistor at the input differential pair.
Touch that leg with a piece of wire, a needle or a small screwdriver, do you hear buzz/hum/click at the speaker?
Be careful not to slip and touch anything else or sparks will fly, plus holy smoke.

[pontiacpete]

I've been starting it up on the variac with an ammeter across the mains fuse. When I bring it up slowly to about half the line voltage, ammeter reads .8A.
Voltages on the output transistors are as follows
A1216
B -1vdc
C -18vdc
E -.3

C2773
B 1vdc
c 18vdc
E .3vdc

The speaker passing the battery test with a pop. There is a resistor and a cap on the tweeter. Speaker measures 8ohms.
There is no DC on the output with or without the speaker.
Re-soldered the connections on the outputs. When this came to me the molex connector on those transistors seems really loose,,so I started messing with them. My theory is that this is why it failed so soon after I gave it back, That is, the connection to one of the outputs came loose and took out the to fusible resistors and transistor I mention above.
I'm having a hard time finding the differential pair at the beginning of the power amp without a schematic. None of these schematics are the schematic for this amp.
But I know an amp is an amp and they can't be that differnet. So the dif pair must be here somewhere. There are 2 transistors that have a leg connected but they are 2 different types, A970 and C2240. I hope to report back with better info.
But does any of this help?

[pontiacpete]

When I bring up the variac all the way there's 1.2A on the mains. This is a lot of current. Output transistors get hot.
Here are the voltages on the outputs and the drivers and the 2 transistors that come after the D667 driver. Using the CK100 schematic that would be Q3 and 4.
A1216

B -1.2vdc(all voltages DC)
C -38
E -.5

B2773

B 1.2
C 38
E .5

Drivers:

B647
B -1.6
C -38
E -1.5

D667

B 1.2
C 37
E 1.6

This is the next transistor in line after the drivers. It's a C2240

B -.8
C 1.8
E -1.4

B646

B 35
C 1.8
E 38

[Enzo]

Is there a load connected to the output? If so, disconnect it. No load until we have a stable amp not making DC.

IS your bias set all the way cold? Start there before adjusting. Not adjustable? Short across the bias transistor to see.

[pontiacpete]

Load is disconnected. There's no DC on the output.
No bias trim pot, either.
On the CK100 schematic, which would be the bias transistor?

[Enzo]

Q3,4 share that duty.

[pontiacpete]

which legs do I short across?

[pontiacpete]

Ha, no response. Oh well.
I can't help but think of the possibility that these output transistors I bought off ebay could be fakes. Wouldn't be the first time.
Anyway I started it up without them and the amp does not pull so much current at the mains.
I have a drawing of the output section that I've been working on. It is very similar to the CK100 schematic. Hope to get that posted soon.
All components on the board are testing good, also, so I'm still stumped.

[pontiacpete]

Finally got the sound back, whew! but it's still blowing the 3 amp mains fuse when played hard and loud. Perhaps it's back to having a high bias but I"m still not sure how to lower that.
Still in the process of drawing out this part of the output section.

[Enzo]

Are you using slow blow fuses as the drawing asks?