VOGONS


faulty SCC-1?

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First post, by Trizz

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Hi there and greetings from Germany!

I've been reading quite a lot here recently to figure out which MIDI devices might be most suitable for my personal DOS-gaming (re-)experience and how to connect those devices sensibly. Thank you for all this great expertise here, it is fun to read and extremely helpful when getting my MT-32 a couple of weeks ago. Luckily, I have managed to keep some contemporary hardware, among which is a Roland SCC-1 which might have become faulty, at least partially. Let me try to give a proper error description here:

The card used to work fine in two old Pentium-I systems (P75 and ASUS T2P4, SBpro2, IDE2CF, S3 Trio64DX PCI). I bought the MT-32 to experience the Strike Commander Soundtrack as it was meant to be. I hooked the MT-32 up to the SCC-1 because it has the required intelligent MPU401 interface. All that worked fine and I was getting amazed by the MT-32 soundtrack. One day, I tried DOOM (configured to General MIDI) and reconnected the output of the SCC-1 to the SBpro. This is when I first realized the problem of my SCC-1, which wasn't there earlier.

Whenever I use the SCC-1 to play MIDI (=GM games), I can hear the first second or so playing, but then some harsh noise overlays the music and gets louder and louder. When I quit the game, the noise remains at its peak. It is only when I do a GS-Reset (in the CHKSCC utility) that the noise stops (or press the reset button on the PC). It only concerns the internal MIDI synth, not the MPU401-part because the MT-32 music is still fine. This noise is audible with any output jack from the card. It can also be reproduced on another P200MMX system. Therefore I am certain that there is something wrong with the card itself. I tried to record the noise with my phone.

I used the demo songs from the CHKSCC utility to demonstrate the issue. Oddly though, song 4 seems to play fine, the other 5 all produce the noise after a second or so. The clip starts with song 4 and ends with the noise in song 1.

When I did some research on this problem here, I read about some amazing experts here capable of diagnosing faults by just looking at photographs of the board - perhaps you can spot a leaked cap or anything else...

I wonder if I can save the GM-section of the card somehow.

Thanks in advance,

Trizz

Reply 1 of 7, by Cloudschatze

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Pin 50 on the core PCM chip, R15239148, appears to be bent and touching pin 49. Separate those, and see if it makes any difference.

Reply 4 of 7, by Trizz

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That really did the trick! My SCC-1 is working properly again, I still can't believe it. Words can't express my gratitude, Cloudschatze. You are amazing.

I must have slipped and bent that pin when reinstalling the card . Finding a small enough flat screwdriver wasn't exactly easy, but separating the pins was harder than expected, since I didn't want to end up with a torn pin.

It is also worth noticing how much this old hardware can take of what was essentially a short circuit.

Thank you once again for making my day and fixing the SCC-1!!!

Trizz

Reply 7 of 7, by Cloudschatze

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Glad that did the trick. 😀