VOGONS


First post, by Kahenraz

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This thread is a follow-up on a post I made elsewhere:

Re: Does anyone else have any issues with the "MIDI IN 1" socket on their SC-55mkII?

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

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.

Also mentioned in the other thread was the discovery of damage to traces on the board. This damage appeared unrelated and did not affect functionality that I could tell; I only use a limited subset of the device to play music from video games.

After my repair I found that it continued to play out of tune. While troubleshooting this I discovered it to be some kind of a bug with this particular board or firmware revision. I remove the coin cell batteries in all of my synthesizers to avoid any chance of corrosion and this was an unexpected side effect.

For this unit, power cycling without a battery will cause the synthesizer to be out of tune. Manually resetting the device using the buttons on the front panel after powering it on will fix this problem but it will detune again after the next power reset. Keeping a coin cell battery installed will retain the correct tuning between power cycles. A front panel reset must be done after installing a new battery; simply installing a battery will not fix the problem.

It's interesting that retuning the device is successful only by the front panel. Sending a GS/GM reset SysEx command will NOT fix the tuning problem.

My mainboard revision is 7543605000 and the ROM firmware is version 1.00. I've included photos of these as well.

See attached for some example recordings.

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Last edited by Kahenraz on 2022-01-18, 21:29. Edited 5 times in total.

Reply 1 of 6, by keropi

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I have not heard of this before
I owned two MK2s both without batteries and never had this
the one I still have does not exhibit this

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Reply 2 of 6, by Kahenraz

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Can you confirm the firmware revision? And if it's identical, would you mind checking inside for a different board revision or chips?

My board also has a couple of factory bodge wires. Does yours have these?

I've added some photos of the other major chips here as well for reference.

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Reply 3 of 6, by Kahenraz

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When after replacing the battery, I found that the unit defaults to an oddball instrument configuration. To clarify, this state only occurs between the new battery being installed and prior to the device being reset. After the battery is installed and the device is reset, the instruments are correct.

Also of note, the only way to fix this is to reset the device from the front panel. Sending a GS/GM reset SysEx via MIDI file will not correct the instrument layout.

Here are some recordings of this strange instrument arrangement, just for fun.

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Last edited by Kahenraz on 2022-01-18, 22:01. Edited 1 time in total.

Reply 4 of 6, by keropi

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yeah there is something wrong with the unit this is not a case of battery present or not or fw/chip versions
maybe some trace or something is still damaged?
what happens if you play the built-in demo songs without the unit being connected to anything other than power + speakers? do they sound bad too?

🎵 🎧 PCMIDI MPU , Orpheus , Action Rewind , Megacard and MK8330 soundcard website

Reply 5 of 6, by Kahenraz

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I've clarified by previous post. The strange instrument layout only occurs between the point at which a new battery has been inserted and prior to the device being reset. This is not something that persists after the device has been powered off.

Have you ever tried playing music on your device after installing a new battery?

Reply 6 of 6, by keropi

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ah that is a different matter then
no I have not tried what you say, I get rid of batteries and call it a day 😁

🎵 🎧 PCMIDI MPU , Orpheus , Action Rewind , Megacard and MK8330 soundcard website