VOGONS


First post, by Kahenraz

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I am having an issue where my SC-55mkII will only receive MIDI commands from the "MIDI IN 2" port on the front. The rear port does nothing. I have tried performing a hardware reset and the switch on the rear is correctly set to "MIDI". My firmware version is 1.00.

I have had this unit for several years and purchased it used. I don't know its history and can't recall if this is something new or if it has always had this issue since I owned it. I don't have any problems with the rear ports on my SC-55 or SC-88VL.

If you don't have this issue, would you please check to see what firmware version it has to compare? To find this information, set the unit to standby by pressing the power button (the orange power LED will remain lit). Then press the left and right buttons for both "INSTRUMENT" and "MIDI CH" simultaneously. The firmware version should then display on the LCD.

Reply 1 of 14, by darry

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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).

Reply 3 of 14, by keropi

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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

🎵 🎧 PCMIDI MPU , Orpheus Soundcard , Action Rewind and Megacard website

💻 WTB Amstrad PC7486SLC-33

Reply 5 of 14, by Kahenraz

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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.

Attachments

  • Filename
    sc7_duke3d_theme.mp3
    File size
    1.52 MiB
    Downloads
    5 downloads
    File license
    Fair use/fair dealing exception
  • Filename
    sc55st_duke3d_theme.mp3
    File size
    1.53 MiB
    Downloads
    5 downloads
    File license
    Fair use/fair dealing exception
  • Filename
    sc55mk2_100_duke3d_theme.mp3
    File size
    1.55 MiB
    Downloads
    5 downloads
    File license
    Fair use/fair dealing exception
  • Filename
    sc55_121_duke3d_theme.mp3
    File size
    1.52 MiB
    Downloads
    6 downloads
    File license
    Fair use/fair dealing exception

Reply 6 of 14, by Kahenraz

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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?

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IMG_20220117_195354_resize_56.jpg
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IMG_20220117_205302_resize_68.jpg
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Reply 7 of 14, by darry

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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 […]
Show full quote

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 .

Reply 9 of 14, by Kahenraz

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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.

Reply 10 of 14, by Kahenraz

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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.

Reply 11 of 14, by keropi

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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 😀

🎵 🎧 PCMIDI MPU , Orpheus Soundcard , Action Rewind and Megacard website

💻 WTB Amstrad PC7486SLC-33

Reply 13 of 14, by M-HT

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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

Reply 14 of 14, by Kahenraz

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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.