Hunting down a flaky RAM chip in a classic computer can turn a fun restoration into a slow, frustrating game of chip-swapping. A new open-source board aims to end that: Tube Time’s Pico DRAM Tester, built around an overclocked Raspberry Pi Pico 2, promises a clean verdict on old DIP dynamic RAM chips from machines like the Commodore 64 and ZX Spectrum.
The tester was highlighted this week on Pimoroni’s blog, where it appeared via a review for the Adafruit 1.14-inch 240×135 color TFT display used in the build. That small screen is the tester’s control center, showing test results and menus while a rotary encoder handles chip selection.
Full-speed testing changes the game
Instead of feeding chips through slow, simplified pass/fail routines, the Pico DRAM Tester checks them at their actual working speeds. The RP2350’s built-in high-speed PIO processors are overclocked to 300 MHz, giving a timing resolution of 3.3 ns. That’s fast enough to catch marginal DRAM chips that can behave badly in a real machine while still passing slower, more forgiving testers.
In practice, this matters for machines like the Atari 800 XL, where erratic behavior can come from memory that technically works but fails to meet timing specifications. The test routines run on the Pico 2’s second CPU core, leaving the first core free for the display interface.
A deliberately simple board
The hardware is refreshingly approachable: a two-layer PCB measuring 100mm x 100mm and 1.6mm thick, designed for fabrication at any PCB house. You can populate only the sockets for the memory types you plan to use, or load them all. ZIF sockets are the recommended choice, letting you lock a chip in place with a small lever.
A 4116-class chip needs more than just 5V, so the board includes onboard DC-DC modules to generate the extra -5V and +12V supplies. You can also skip those modules and feed all three voltages in from a bench supply, which opens the door to voltage-margin testing. If you don’t plan to test 4116 or 4132 chips, those converter parts can be left off entirely.
The project’s latest revision adds a USB-C power connector with PD resistors, universal encoder wiring for both Bourns- and Panasonic-style encoders, and a through-hole footprint for the Pico 2. It’s worth noting that the board requires a Pico 2; a Pico 1 won’t work.
Tests that dig deeper than ‘does it boot?’
The firmware runs three main families of tests: March-B, pseudorandom, and refresh. March-B is a linear sequence of reads and writes designed to catch address-decoder faults, stuck-at faults, transition faults, and coupling faults. The pseudorandom test runs through 64 repeatable patterns and reads each back, hunting for pattern-sensitive problems. The refresh test waits longer than a typical refresh interval before reading back, exposing data-retention issues.
Supported chips in the project’s list range from the 4027 up to 256K parts, including the 4116, 4164, 41128, 41256, 4416, 4464, and 44256. Firmware updates have also added support for the half-good 4108 and 4132 chips found in some 8-bit computers.
What the build looks like
Lee from More Fun Retro put together a video covering the full assembly and testing process, comparing the board with other retro chip testers. A separate build from Root42 shows how tweaking one line of PIO timing code in the open firmware can fix compatibility with Samsung DRAMs that initially failed—a good example of what open-source tooling allows.
Once assembled, the workflow is simple: install the chip in the socket for its memory type, rotate the selection knob to the right part number, choose the speed grade, and push the knob to start. The screen shows a red X for a failed test or a green checkmark for a pass. The design also notes that if you run the board from a computer’s USB port, you may get a lower voltage that can cause good chips to fail; a proper 5V supply avoids that pitfall.
The schematics, bill of materials, and fab files are all available on GitHub, and the project is licensed under Creative Commons Attribution-ShareAlike 4.0.









