Leningrad-2-128k-SRAM (Aurora)

Leningrad-2. Russian ZX Spectrum clone with SRAM. Schematics and PCB.

English | Русский

Following the successful launch of the Leningrad-2-48k project and incorporating community feedback, this version transitions from dynamic RAM (DRAM) to static RAM (SRAM).

This architectural shift required a significant redesign of the memory management unit. As a direct benefit, the system memory has been expanded to 128K directly on the mainboard without requiring any external expansion daughterboards.

Additionally, the freed-up PCB space allowed the integration of two YM2149F sound chips, providing "out-of-the-box" Turbo Sound support (by NedoPC). An IORQ arbiter was also added to the schematic.

The final result of these upgrades is the "Leningrad 2 NEXT 128K + TS 2025" motherboard. Following hardware assembly, testing, and minor debugging, the project was officially given a new name by close friends: "Aurora".

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Revisions & Hardware Modules

Mainboard Revisions

• Revision 2.01 (Schematics / Gerber) — Initial release. Features a humorous design note: at the urgent request of the PCB manufacturer, the board text was changed from "Made in..." to "Designed in..." ;)
• Revision 2.02 (Schematics / Gerber) — The latest stable revision. Adds a power LED indicator and fixes the joystick port routing.

Bus Adapters & Expansion Boards

• Nemo-bus and ZX-bus Adapter (Gerber) — Differs from the previous project version by routing the /IORQ-GE signal directly to its intended destination. On older Revision 1 adapters, /IORQ-GE went to pin A19 (+beta); it now routes to pin A17. To upgrade a Rev 1 adapter to Rev 2 specs, simply cut the trace going to A19 and solder a jumper wire to A17.
• "Yolka" (3x Nemo-bus & 1x ZX-bus) Slot Expansion Board (Schematics / Gerber) — An expansion backplane made possible by the new onboard hardware arbiter.
• Upgraded Slot Expansion Board (Schematics / Gerber) — A redesigned backplane where the ZX-bus connector is replaced with a standard Leningrad-2 edge connector. It also adds a dedicated +5V/+12V power input molex. Vintage ZX-bus cards can still be connected here using adapters (First / Second).

Keyboard PCB Options

Two mechanical keyboard variants were designed for different mounting styles:

1. Chassis Mounted: Designed to fit directly into a computer case (Gerber).
2. Sandwich / Double-Decker Mounted: Designed to stack directly on top of the mainboard (Gerber).

• Mechanical Switch Support: Dedicated PCB layouts have been added for ReDragon-MX-ZT02 (Gerber) and ReDragon_Slim_ZT04 (Gerber) switches.

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Assembly & Jumper Settings

In general, hardware assembly and tuning are straightforward. The functions of the onboard configuration jumpers are as follows:

• JP1, JP2, JP3: Short these if you are installing a standard VGA video connector. Leave them completely open for HDMI output. If using HDMI, make sure all resistors R24-31 are replaced with 270 Ohm.
• J9: Used to isolate and disconnect power from the RP2040-Zero board while flashing video firmware.
• J12: Used to switch between Beta Disk Interface (BDI) firmware banks if you install a 27256 EPROM containing two separate versions of TR-DOS.

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ROM & Video Configuration

• ROM: Detailed EPROM files and configuration info can be found here.
• VGA: Firmware and instructions for the RP2040-Zero converter are available here.

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Recommended Accessories

• BDI-TR-DOS
• DivMMC
• LGT-Turbo-Sound-emulator
• ZX-EQ Nemo-bus Edition

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Credits & Acknowledgments

• Alex Ekb (Aleksey) — for the incredible RGB2VGA converter design.
• HRDY (Dmitry) — special thanks for his invaluable technical advice, consulting, and support.
• The Scorpion ZS & Leningrad community, and all friends who helped bring this project to life.