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Old 09-15-2020, 02:04 PM   #1
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Default Need Help with Roland SC-88 Pro distorted sound!

Hello All,

I know what I'm asking here is not easy to answer but, here I go anyway. A couple of years ago I got a Roland (Sound Canvas) SC-88 Pro, 120v version, it was like new, manual, original box, everything was great, not a scratch. Played with it for a couple of months and it worked as expected. A few days ago I wanted to use it again and now the sound it's completely distorted, it's like a big crackly sound (I'm attaching a sample using the sound preview button: one short press, one long and another short at the end) .

So, I opened it up and noticed that in the main board, some of the Alum/Poly (smd) caps leaked, not a lot but they did. I replaced them (8) with spare ones I got from Digikey, nicely done, no traces lifted whatsoever and used the same values of course but, that didn't fix the problem. I got the Service Manual and compared the voltages from the transformer, there are 5 output pins as you can see in the picture. I did two tests, one with the transformer on it's own, cable disconnected from the Main board, and the second with the cable connected.

My readings with a Fluke multimeter: (AC)
with the cable disconnected from the main board:
on the 12v ones I get 16.77v each
one 5v gives me 6.22 and the other 2.17

with the cable connected to the main board:
on the 12v ones I get 16v each
the 5v are aprox. 3.98v each

Either way, theses numbers are all wrong, correct? am I missing something? I don't see any signs of heat damage or leakage (except the caps I mentioned from the Main board), everything looks good, no funny smells, etc. If the voltages are all wrong, that probably damaged some chips, right? I guess replacing the transformer would be too late... (not to mention finding a replacement).

More finds:
I tested some voltages that go to the main board and got these values: (DC) 4.9v, 3.6v, 2.48v, 0.9v, some numbers look really odd but I don't know.
In the "analog" or secondary board, the (Japanese) electrolytic caps look in great shape, no swollen or leakage. Also, I did a test with the line-in and the sound is correct, no problems there.
Midi inputs get the signal but, that's when audio gets bad, same if I press the Preview button.
Display and buttons have no problems at all.

I did some of the tests from the Service Manual and got several errors with the "Memory Test", I'm attaching a screenshot of what the manual says it's wrong, it matches exactly with what is reported on the screen. The thing is, sometimes a bad component can trigger a chain of errors which is what I think is happening here but, I'm no expert.
I looked at all those chips but I can't find broken traces or burn marks.

I want to fix this thing so bad!! Any ideas?

Thanks for reading!
Attached Images
File Type: jpg Power Diagram.JPG (41.9 KB, 6 views)
File Type: jpg Transformer.jpg (588.7 KB, 9 views)
File Type: jpg Display errors.jpg (460.9 KB, 9 views)
File Type: jpg Test Diagram.JPG (69.3 KB, 9 views)
Attached Files
File Type: zip Roland SC-88 Pro Sound (417.7 KB, 2 views)
File Type: zip Roland SC-88Pro Service (4.40 MB, 2 views)
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Old 09-15-2020, 11:15 PM   #2
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Default Re: Need Help with Roland SC-88 Pro distorted sound!

A little clarification, one of the ribbon cables that goes to the Main Board, attached near the transformer on the secondary board, reads 4.95v (DC) at two points, this may be a correct voltage. Another ribbon cable that is coming from the other end of the secondary board (passing thru the analog section, I guess), is where I get the other voltage readings (3.6v, 2.48v, 0.9v), this probably makes more sense... ? I'm starting to think that maybe the voltage is not the problem.

Last edited by Dusko75; 09-15-2020 at 11:16 PM..
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Old 09-19-2020, 02:22 AM   #3
Per Hansson
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Default Re: Need Help with Roland SC-88 Pro distorted sound!

That is a bit strange, the fact that you can use line-in with no noise means the problem is not in the analog audio output stage.
So it must be something that goes wrong in the MIDI decoding stage of the unit.
Maybe send the sound file you recorded to Roland and see if they are willing to offer any advice?

P.S: Just to rule it out have you tried other cables?
I thought I had a bad Roland but turned out to be just a bad RCA audio cable with intermittent connection!
"The one who says it cannot be done should never interrupt the one who is doing it."

Last edited by Per Hansson; 09-19-2020 at 02:23 AM..
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