Hi,

While I'm not familiar with the SC-88 Pro, I would also consider a failed capacitor to be the primary possibility of what have gone wrong. The other issue that can cause such progressive disruption of waveforms is overheating, but if the components were "happy" without a heat-sink before, then it is unusual to start showing overheating issues now.

Hopefully someone who is more familiar with this particular Sound Canvas model comes along, they might have a more exact troubleshooting tips regarding this model.

One thing that should definitely be looked at is the (now) brown glue used to fixate C125, C126, C141. That's reported to become corrosive and / or conductive from its original state and imho should be removed.

I was here thinking that was just old flux, good to know. how would I remove that?

I am familiar with repairing/recapping several Roland SC units.

The Roland service manual (or "Service Notes" as they call it) are available for the SC-88 Pro, which has full schematics. While I haven't personally work on the Pro model, I will say that diagnosing my own malfunctioning SC-88 was easy enough that I consider that experience "fun."

EzoGaming wrote on Yesterday, 19:53:

Rom test returns OK.

So you get the "OK" on the LCD when doing the memory test? Does it still pass the test after the unit had been on for a while and experiencing the audio glitches?

EzoGaming wrote on Yesterday, 19:53:

It wasn't until this year that I found out the transformer can be rewired for 120V, as well as it wasn't until this year that I finally had equipment for soldering. But not desoldering (I need the braid).

You don't need desoldering braid for the transformer re-wire. You should be able to apply heat up the existing solder on the 100V transformer primary lead, then grab the black lead and pull if off. (Safety goggles are a must, and be careful not to fling solder towards you) Or better yet - leave the existing solder alone, and cut the black wire exposed right where the insulation ends. Re-strip the black wire, wrap it around the 120V terminal, solder.

Running a 100V unit on 120V should not significantly impact the DC (+5V, +12V, -12V) outputs - the regulators may run hotter though. But, 20% overvoltage may have impacted the larger smoothing caps before the regulators. I don't recall the voltage ratings to determine if there is enough margin in the design, but that may be irrelevant anyway, considering the age of the original caps, and that these would be mostly likely to experience an electrical failure.

EzoGaming wrote on Yesterday, 19:53:

Likely culprit? One of the capacitors failed. None of the ones on the boards look busted so it was likely an internal failure.
...
What's the actual manifestation of the fault? The audio starts out clean once the unit turns on from cold boot, then over time the audio will start crackling and decaying until the audio is very quiet and clipped (the bits are decaying so to speak). It happens before DAC but after processing. It gets to a point where audio can only be heard if the channel volume is set to 1, drums are disabled, and the gain on my PC is set very high. The fact that it happens over time from a seemingly clean state upon boot really tells me it's one of the capacitors.

I think you are on the right track, however, I would not limit the failure suspects solely to capacitors. The pattern you describe definitely sounds like thermal expansion. That can be capacitors, but it can also be as simple as cracked solder joints, or literally anything else where an intermittent failure is temperature-dependent.

Have you removed and inspected the bottom of the power/analog board? My SC-88 arrived with several cracked solder joints, on the RCA jacks in particular.

Listening to your recordings, I agree that this does not seem like an analog failure. It also seems like your digital section is more functional that not.

The SC-88 (non-Pro) I purchased ~6 years ago stopped working recently. In my case, it was loud digital popping almost immediately after power-on, which turned out to be leaking SMD electrolytic caps on the digital board that ate a trace to the RAM chips. When I had it open to replace the battery years ago, there were no signs of cap leakage. From what I can see in your photo, I do not see obvious signs of this corrosion on the digital board, but I cannot see enough detail to rule that out. Your failure also sounds different.

In your shoes, I would assess the outputs of the power supply - voltages, ripple, etc. Do you have a multi-meter and/or oscilloscope?

I would also try disconnected CN5/CN105, which is the digital audio from the digital board to the DAC on the analog board. You will not get any audio in that state, but if you still get noise (after it warms up), then you know there is a problem with PSU or analog section.

As for cap replacement, I would focus only on C125, C126, and C127 for now.

MJay99 wrote on Yesterday, 20:24:

One thing that should definitely be looked at is the (now) brown glue used to fixate C125, C126, C141. That's reported to become corrosive and / or conductive from its original state and imho should be removed.

I agree. I have professional experience repairing electronics (70's-90's HiFi, turntables, etc) and have encountered chemical breakdown issues with the circuit glue used on the larger electrolytic capacitors. It will actually get corrosive enough to eat away components leads.

That is C125, C126, and C127 with glue. C141 is the small electrolytic without glue in the photo, the label for C127 is hidden in the photo.

And sorry, I really don't like being the correction guy, but mentioning for clarity to the OP.

EzoGaming wrote on Yesterday, 20:27:

I was here thinking that was just old flux, good to know. how would I remove that?

It is indeed circuit glue. It is typically used on physically large/heavy capacitors, to prevent both mechanical strain and resonance.

Once the capacitors are removed, I would recommend scraping the glue off. It is very hard and brittle. I use metal picks - the best is one that looks like a flat head screwdriver that is sharper on 1 edge, and a pointed dental pick for any glue under/around other component leads. After, I do a cleanup with swabs and isopropyl alcohol.

I have tried mild through moderate strength solvents with no effect, stopping short of strong solvents that would definitely damage other components and/or the PCB itself. In other words, don't bother with chemical removal - unfortunately this requires scraping effort either way.

Wow, a lot to unpack here.

"SC88Pro has service notes" Yeah i've been through those.. though i definitely need to take another look and reassess them

"Does it still pass the test after it had been running" Yes

"Have you inspected the bottom of the analog board" No, actually. Never occured to me. I should tomorrow.

"Do you have a multimeter or oscilloscope" Unfortunately not, not yet, and I am aware that its something I am going to need for a repair project like this. Once I get my financial situation figured out

"I really don't like being the correction guy" I already learned about the glue from Mjay's reply it's all good

I'll also remove the glue when i get to the analog board.

Agh, i dont know how to edit posts, i can't remove the glue tomorrow because i can't desolder the capacitors yet, 🤣

Triple post: I realize i can at least remove the glue AROUND the caps which i might as well do. I feel like the dunning kruger is strong with me 🤣

First off thank you for the images, now I know where the battery is when I eventually have to replace it on mine 😀

For rewiring the transformer: I personally wasn't able to desolder the black wire on mine. It might be because I was using a very old iron without temp. control but the plastic around the solder joint would start melting before the solder. The wire was also tightly wrapped around the pin on the transformer. I ended up cutting of the very end of the black wire, stripping the end and resoldering to the '120' terminal before doing any real damage to the transformer.

TheMLGladiator wrote on Today, 11:46:

For rewiring the transformer: I personally wasn't able to desolder the black wire on mine. It might be because I was using a very old iron without temp. control but the plastic around the solder joint would start melting before the solder. The wire was also tightly wrapped around the pin on the transformer. I ended up cutting of the very end of the black wire, stripping the end and resoldering to the '120' terminal before doing any real damage to the transformer.

I recommend cutting and resoldering as well. I did desolder the wire on my own SC-88 Pro and ended up melting some of the plastic in the process.

EzoGaming wrote on Yesterday, 19:53:

What's the actual manifestation of the fault? The audio starts out clean once the unit turns on from cold boot, then over time the audio will start crackling and decaying until the audio is very quiet and clipped (the bits are decaying so to speak). It happens before DAC but after processing. It gets to a point where audio can only be heard if the channel volume is set to 1, drums are disabled, and the gain on my PC is set very high. The fact that it happens over time from a seemingly clean state upon boot really tells me it's one of the capacitors.

In my experience failing capacitors usually have the opposite symptoms. Audio problems would manifest on cold boot, but as the unit warms up things would stabilize. The capacitors are also not showing any physical signs of failure in the photos posted, though admittedly that's no guarantee. But I wouldn't suspect the capacitors themselves at first glance.

I agree with Fazeshift's assessment that it's likely some sort of thermal expansion issue as the unit heats up.

One way to diagnose this is to run the unit with the board exposed and use a can of compressed air to cool down components as the unit runs. This might help pinpoint where it is failing.

Removing the capacitor glue is also a good idea. That could also potentially short the capacitor. As some of the glue has gone quite dark, it's likely conductive at this point.