SC-88 pro spitting noise

[FalCT60]

Hello,
Awhile I didn't come there. Everything was fine so far.
My old SC-88 pro began spitting a few days ago. Rather softly at first, but more and more loudly then, and regardless of playing sounds or being idle.
I gave up searching for repair service in my area, so I wish it should be only dried capacitor to be replaced, since cms are far over my skill.
I have disassembled the device, the audio board is the lower one.
I'd greatly appreciate any tips that could help me briging it to work.
Rgrds,
J.-Luc

 

[Gourockian]

That definitely sounds like a capacitor or some capacitors going bad. Can you post some pictures of the boards so we can see the components?

 

[FalCT60]

OK, so I'll order all the chemical ones that populate the board and replace all of them.
Here are the photos you asked for, components side and soldering side.
Thanks for replying.

 

[Gourockian]

I take it you mean electrolytic when you refer to "chemical ones". Before you go crazy replacing them all, I would carefully check the ones I've marked in red as it looks like there may be leakage from these. It's difficult to tell from the pictures if the brown areas are leaked electrolyte or just compound that was placed to 'anchor' them.

Also, make sure there are no capacitors that show signs of bulging on the top as that would definitely be a sign of failure. Again, it's difficult to be certain, just looking at the picture but they do seem to be bulge-free. At least, they all have straightforward through-hole wires which will make them easy to remove and replace, if necessary.

The white dots on the PCB refer to the negative wire so watch for that when replacing any. If you have a problem getting the exact replacement of capacitance value and voltage, always try to get the same capacitance and if necessary, a higher voltage rating - never go lower. It might be slightly bigger but you have enough space to cope with that.

I hope this helps and that you manage to fix the issue. I had a similar problem with an organ and ended up replacing 74 surface mount capcitors, which was a good bit more difficult but it did cure the noise issue.

 

[FalCT60]

Yes... electrolytic. I sometimes can't find the words I need.
According to the texture of the brown substance, I think it's compound, though I wonder why they needed to anchor thoses components. They wouldn't escape anyway.
Well... I think I accidentally just found the culprit ! I had examined board carefully, with a magnifier, but I missed something: the welds of the transistor without a heat sink to the right of the two capacitors are loose. Stupid me ! I have focussed on the capacitors and didn't pay attention to anything else.
I'm going to fix that, and swith the mains from 120 to 240V as well, that's just a wire to move from one pin of the transformer to another. And get rid of this 120 to 240 converter.
I come back and report the progress.

 

[Gourockian]

It's quite common to see the larger capacitors of the power supply circuit secured by glue or compound. I think it is to prevent vibration but not too sure.
Loose connections would be a very likely source of the noise you are describing and from what I can see, it definitely looks like the solder blobs are different for IC105, compared to others. Ususally, dry joints, as they are called, are not usually found on good quality circuit boards but it is not impossible. I would go over each one very carefully in case there are other problem joints.
I used to have an SC-55, the first Sound Canvas that Roland produced and still have the original 240v power supply with a UK 13-amp plug. However, I'm in the US now so it would be expensive to ship it to you, if you were interested in it. Switching the pin is your best option.

 

[FalCT60]

Well, it was the culprit.
I reassembled it and when pushing the knob I can hear clear and continuous non-distroted sound.
But now there is not midi input anymore : when connected to my computer, it can't play anymore.
I feel quite disappointed. I hope I can fix this soon.
The power supply of the SC-55 (I own the MK-II) is different form the SC-88's.
In the former, it's a separate PSU where in the later it is part of the device..

 

[Gourockian]

Well, it was the culprit.
I reassembled it and when pushing the knob I can hear clear and continuous non-distroted sound.
But now there is not midi input anymore : when connected to my computer, it can't play anymore.
I feel quite disappointed. I hope I can fix this soon.
The power supply of the SC-55 (I own the MK-II) is different form the SC-88's.
In the former, it's a separate PSU where in the later it is part of the device..

That's good and not so good news. I'm assuming that you do have them connected properly - Midi In to Midi Out? I've been guilty of making that mistake a couple of times. if they are okay, it may be worth spraying the midi sockets with something like Deoxit or another contact cleaner and plugging and unplugging the cable a few times. It also wouldn't do any harm to try a different midi cable.

It's unlikely that you have caused the midi issue directly when you had it opened up but possibly indirectly, by disturbing another dodgy solder conection. I would suggest rechecking all the solder points.

If you are still having problems, it would be worth installing Midi-Ox on your computer. That will allow you to monitor the midi signals and may help to pinpoint where the problem lies.

I should have realised that the SC-88 has a built in power supply after seeing the rectifiers and smoothing capacitors - duh!

I hope you get your midi issue sorted out and get back to making music. Good luck.