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SC-88 repair?

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First post, by Wanny

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I'm new to this vintage hardware. I got myself a Roland SC-88 some months ago and it was working perfectly until yesterday morning...

I came back from Christmas dinner and wanted to do some stuff with it, but when I turned it on I heard a nasty static sound. If I press the Preview button I can vaguely hear a note, and if I play something through MIDI I can hear notes as well, but with the constant static noise on top.
I replaced the internal battery with a brand new CR2025 (it's the same as a CR2032 but a little thinner) since I was getting a LOW BATTERY message on powerup. The error disappeared but the noise problem persisted.

I found a link for the service manual ( here), followed the instructions for the Test Mode and...
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The blinking number is D1, meaning that one of the DRAM chips went bad. According to the service manual it's a M5M44256BJ-7 chip.

Has anyone run into this issue?

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Also, unrelated to the issue, I noticed that the transformer has many voltages (100, 230, 250, etc) next to unused pins. Is it safe to assume that I can desolder the cable from the 110 pin and connect it to the 230 one to avoid having to use stepdown transformers? (we use 230v in my country)

Reply 1 of 7, by cyclone3d

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I haven't run into that problem on a sound module.. but RAM can go bad.

If it was me, I would try re-flowing the solder on the RAM chips first. It could just be a bad solder connection.

A hot air soldering gun and some no-clean flux would work very nicely.

You will want a hot air soldering gun either way if you want to repair it yourself if a RAM chip is indeed bad.

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Reply 2 of 7, by keropi

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About the transformer - there is another thread here and it works like you say, you can move the cable to 230v and it will work. Better search for the thread but I am 99,9% sure it works like that.

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Reply 3 of 7, by SirNickity

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Check the internal power supply rails. If the PSU is failing, you're going to get all kinds of flaky behavior. Could be the RAM is fine, it's just not running stable.

Reply 4 of 7, by Wanny

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keropi wrote:

About the transformer - there is another thread here and it works like you say, you can move the cable to 230v and it will work. Better search for the thread but I am 99,9% sure it works like that.

OMG it's true. I'll do the mod tomorrow, that a friend will help me giving it a look (my soldering skills are none...)

It could be possible that the problem was caused by a bad quality stepdown transformer?

Reply 6 of 7, by Wanny

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The mod to 230v was successful. But it didn't fix the main problem 🙁

Reply 7 of 7, by fr0ztz

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Hi!

I'm having the same issue with my SC-88, one night last week it started to snap, crackle and pop.

Seems like the more channels playing the worse it is. When previewing an instrument I can only hear a little static noise.

I'm thinking PSU.

- Did you find out what was wrong with your unit?

Regards.

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