Re: Faulty Roland LAPC-I

Posted on 2019-02-01, 20:11

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

although I have a LAPC-I for more than 20 years now and the service manual for about 2~3 I had no idea there were more roms other than the firmware and samples... never had to look at the service manual and I hope I never have to! :D LOL Yesterday, I did some experiments with changing the control …

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Re: Faulty Roland LAPC-I

Posted on 2019-02-01, 19:47

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

I would assume that the data retention period for the ROMs might be nearing its end of life... if so, that would be easy to fix, since ROM images are available, right? I hope that no other severe damage has been done. This is a mask ROM, and thus it has much longer lifespan than EPROM or flash. I …

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Re: Faulty Roland LAPC-I

Posted on 2019-02-01, 19:03

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

Note that the ROM started failing at around 30°C in the LAPC-I, but it took more than 50°C in the programmer to manifest. If the board was damaged by an ESD-event, other components might start failing sooner or later...

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Re: Faulty Roland LAPC-I

Posted on 2019-02-01, 18:55

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

Do you mind to explain a bit how you found the faults? Thanks to keropi it was quite easy. I located the first fault just by listening to the signal at different spots in the circuit, by "backtracking" the analog signal path from the output connector to the 6 outputs of sample-and-hold circuits. …

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Re: Sound Blaster CT1350B not being detected properly.

Posted on 2019-01-31, 13:36

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

Thanks, keropi!

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Re: Faulty Roland LAPC-I

Posted on 2019-01-31, 13:32

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

Ok, finally solved it. :) The first problem originated in the right low-pass filter. One of its opamps was introducing large amount of noise to the signal — that was easy to fix. The second problem was caused by IC19 — the reverb mask ROM — which was slightly faulty. When its temperature rose above …

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Re: Sound Blaster CT1350B not being detected properly.

Posted on 2019-01-28, 14:57

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by suntac

in Marvin \ Sound

in Marvin \ Sound

How about just using a Game Blaster clone next to the SB Pro? See here: https://www.vogons.org/viewtopic.php?f=62&t=63867 My 286 runs like that. Note that both card's can't be on the same base address (unlike a regular SB 1.x or 2.0, the dual OPL2 or OPL3 is in the same address range as the SAA1099 …

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Re: Sound Blaster CT1350B not being detected properly.

Posted on 2019-01-28, 13:13

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by suntac

in Marvin \ Sound

in Marvin \ Sound

I wonder if it'd be possible to cobble together a CMS add-on for a Soundblaster Pro 1 or 2, since they use the CT1366 or CT1366A. It'd have to be in the form of a daughterboard I guess... anyway, just thinking out loud. :lol: Theoretically yes, but cutting PCB traces and/or desoldering ICs would be …

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Re: Sound Blaster CT1350B not being detected properly.

Posted on 2019-01-27, 20:14

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

I just listed the GAL (/itm/283355371046). The compatibility with CT1336A is explicitly mentioned in the item's description. You're welcome to make me an offer (mention Vogons).

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Re: Sound Blaster CT1350B not being detected properly.

Posted on 2019-01-26, 22:41

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

I may list just the GAL there, if you are interested.

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Re: Sound Blaster CT1350B not being detected properly.

Posted on 2019-01-26, 22:37

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by suntac

in Marvin \ Sound

in Marvin \ Sound

Yes, that's exactly the problem. The GAL is not compatible with CT1336A. I reverse-engineered the differences between CT1336 and CT1336A and wrote a new set of GAL equations compatible with both of them. Selling this kit on eBay right now. 😀

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Re: DTK 386sx board not working with any 8bit sound cards?

Posted on 2019-01-26, 21:52

by

by suntac

in Marvin \ General Old Hardware

in Marvin \ General Old Hardware

You may use a ~47pF capacitor connected in series with two antiparallelly connected red LEDs. Just connect this probe between the TTL/HCMOS oscillator's output and ground and it should light up. If it doesn't, try again with slightly larger capacity. Another low-cost option is to use a cheap Chinese …

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Re: Sound Blaster CT1350B not being detected properly.

Posted on 2019-01-26, 00:42

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

What is your exact CT1350B board revision? Take a look here: http://nerdlypleasures.blogspot.com/2013/06/t … ms-upgrade.html

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Re: Sound Blaster CT1350B not being detected properly.

Posted on 2019-01-25, 21:08

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

Most of the C/MS upgrade kits support only the older CT1336 bus interface chip. If your card happens to have the newer CT1336A on board, both the original and cloned upgrade kits won't work properly and will interfere with the FM synthesis.

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Re: Tube Time: Announcing The Snark Barker, a 100% Compatible SB 1.0 Replica!

Posted on 2019-01-25, 19:12

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

I am a bit wary of joining one of the order lists, as I would like to know whether I would be able to successfully assemble this one, or whether I will have to stop at one point, missing some kind of rare chip or part throughout the way... All the chips used in this design are pretty commonplace. …

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Re: Tube Time: Announcing The Snark Barker, a 100% Compatible SB 1.0 Replica!

Posted on 2019-01-24, 21:47

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

Why do I see the text "(C)1992 Anchor Electronics Co." in the HEX dump?

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Re: Tube Time: Announcing The Snark Barker, a 100% Compatible SB 1.0 Replica!

Posted on 2019-01-24, 21:34

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

Nice work, mate!

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Re: Question about Roland SCC-1

Posted on 2019-01-08, 20:26

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by suntac

in Marvin \ Sound

in Marvin \ Sound

It is an MPU-401 on a chip (RJA-401-HB). It contains the CPU, SRAM and logic array in a single package. The chip on my SCC-1A is marked as 4B1.

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Faulty Roland LAPC-I

Posted on 2019-01-08, 17:26

by

by suntac

in Marvin \ Sound

in Marvin \ Sound

A friend of mine recently bought an old Roland LAPC-I card and asked me to repair it for him. The right channel is much noisier than the left one. I believe I can fix that, but there is another problem. The card usually starts sounding quite weird and distorted (digitally) after a few minutes, 5 or …

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Re: MDA/CGA/EGA to VGA Converter Released!

Posted on 2018-11-30, 10:38

by

by suntac

in Marvin \ Video

in Marvin \ Video

640x480 and 800x600 are on the VGA spectrum. The device does not have memory enough for holding an entire frame. Unless you design a pass-through mode only converting the TTL to analog. But since I don't have one of these and I don't plan buying one I won't bother. Hi retrocanada76, would you be …

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