Assuming it's not disabled in the menu, it could be a hardware fault similar to this one on an MK1https://www.vogons.org/viewtopic.php?p=914821#p914821 or maybe completely different .

I don't have a MK2, unfortunately (or maybe fortunately, as space is running low).

I wasn't able to locate any menu option that would disable any of the ports. I thought this would be the case but I would be surprised if such a thing could survive a reset.

it could also be an issue that the back midi port has broken solder joints - common issue in fact
mine had this issue with the front port and I had to reflow it to fix it

I see I have no choice but to operate. I will report back once I have investigated this further.

Can anyone confirm if there is even an option in the menu to disable one of the MIDI ports?

It seems that there is something else wrong with my SC-55mkII. I knew it sounded strange but now that I have a collection of recordings, I can finally pin it down. It's completely off-pitch! This isn't an issue with just Duke Nukem 3D. The pitch is wrong with anything it plays.

Here are comparisons with my SC-55 (V1.21), SC-55ST and SC-7. The SC-55ST and SC-7 are derived from the mkII and should sound the same but instead they sound much closer to the original SC-55.

I can remember that the guy who sold it to me locally seemed very shifty but it "seemed to work" when I got it. I don't know if he was trying to offload a defective unit or what. I think it would be difficult to tell whether a particular synthesizer is out of tune without a similar model to compare but maybe it's just obvious to someone who composes music often. In my case, I knew my mkII always sounded "weird" but I thought it was just a result of having different samples.

I wonder what's wrong with it?

See attached for example recordings.

I removed the main PCB from the case and upon closer inspection I did locate what appeared to be cracked solder joints on the rear MIDI input connector, but that isn't the worst problem. I also found that the epoxy used to secure one of the large capacitors to the board has turned corrosive and begun to dissolve the copper ground plane and severed a nearby trace.

This is very serious and may be a ticking time bomb in other synthesizers. I will be making a new thread about this to share the problem in detail once I've finished my repairs.

I had the idea that the epoxy might be a problem after remembering Adrian from Adrian's Digital Basement describing this exact same problem in one of his videos. I wanted to link it here but I was unable to find it. Does anyone here remember which one it was?

Kahenraz wrote on 2022-01-18, 01:44:

I removed the main PCB from the case and upon closer inspection I did locate what appeared to be cracked solder joints on the re […]
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I removed the main PCB from the case and upon closer inspection I did locate what appeared to be cracked solder joints on the rear MIDI input connector, but that isn't the worst problem. I also found that the epoxy used to secure one of the large capacitors to the board has turned corrosive and begun to dissolve the copper ground plane and severed a nearby trace.

This is very serious and may be a ticking time bomb in other synthesizers. I will be making a new thread about this to share the problem in detail once I've finished my repairs.

I had the idea that the epoxy might be a problem after remembering Adrian from Adrian's Digital Basement describing this exact same problem in one of his videos. I wanted to link it here but I was unable to find it. Does anyone here remember which one it was?

IMG_20220117_190512_resize_8.jpg

IMG_20220117_195354_resize_56.jpg

IMG_20220117_205302_resize_68.jpg

Hmm, I think it's high time I re-inspected mine .

Hope you can get yours working without too much trouble and thank you for the PSA .

Kahenraz wrote on 2022-01-17, 23:35:

It's completely off-pitch!

Does it react to "key shift" controls with the front panel buttons?

I will check once it's reassembled.

I did a full reset of the device between each recording and all of the tracks from this device are off-pitch. So it's not something that resulted from an accidental bump.

I managed to fix the rear MIDI input port; it was definitely a cracked solder joint. There were some other suspect joints as well so I ended up cleaning away and applying fresh solder for all of the pins on the input port, the ground connectors on either side (which also act for mechanical strength) as well as the pins for the RCA input/output.

Also of note, the entire rear PCB is covered in a thin layer of dried flux residue as a result of the wave solder process. It can be seen as a reflective sheen; this is actually the flux and not the texture of the solder mask. Gross!

Disassembly to the mainboard of these units is tedious so I wanted to touch anything that would have gotten the most mechanical stress preciously and in the future.

vstrakh wrote on 2022-01-18, 08:29:

Kahenraz wrote on 2022-01-17, 23:35:

It's completely off-pitch!

Does it react to "key shift" controls with the front panel buttons?

The key shift does alter the output but shifting it in this way distorts it further from normal.

I need to also check my units for the glue deal, might as well remove it just to be safe
glad you fixed atleast the jack issue 😀

See here for why the synthesizer was out of tune and how to fix it.

The Roland Sound Canvas SC-55mkII may be out of tune when powered on without a battery

Kahenraz wrote on 2022-01-18, 01:44:

I had the idea that the epoxy might be a problem after remembering Adrian from Adrian's Digital Basement describing this exact same problem in one of his videos. I wanted to link it here but I was unable to find it. Does anyone here remember which one it was?

I think you mean this one:
https://www.youtube.com/watch?v=mLVbmnViz7I

Yes, thank you! The adhesive in his video appears to be the same color and consistency as what I saw. The major difference between it and the other adhesives I found elsewhere is that it was hard and dry with an opaque brown color consistent throughout.