Tom Verbeure Upcycles a Compact Sony CRT From an HP Logic Analyzer for a Retro Gaming Build
Destined to provide a smooth picture for vintage games, this old Sony CRT is being freed from its home in an old HP logic analyzer.
Hardware engineer Tom Verbeure found himself with a long-outdated Hewlett-Packard logic analyzer, and after taking it apart found himself face-to-face with a compact Sony cathode-ray tube (CRT) — so set about turning it into a functional monitor for a compact retro gaming machine.
"I disassembled an HP 16500A logic analyzer," Verbeure explains. "There wasn’t much to it other than getting a look into a old dinosaur of a machine, but one thing that caught my attention was the CRT unit: Unlike most other old CRT-based test equipment, such as my Tektronix TDS 420A oscilloscope, the CRT of HP 16500A is not an integral part of the machine, but it’s a self-contained module that can easily slide out of the main chassis and wired up independently. It’s a tiny little monitor! It made me wonder if there’d be some to use it in some creative ways?"
The monitor in question is a vintage Sony, built around a 10" Trinitron cathode-ray tube (CRT) offering a visible screen area of 9". The service manual for the HP logic analyzer in which it was installed offers details of which pin on its connector are designed for which signals — offering a way to feed it red, green, and blue image data plus horizontal and vertical sync.
"The voltage levels for the sync signals are a standard 5V TTL (good!), but the voltage levels for the analog signals are weird, with a baseline of -1.7V and a maximum value of 125mV (WTF?), or an amplitude of 1.825V," Verbeure discovered. "I was initially hopeful that it’d be easy to drive the CRT module with something that was similar to a standard PC VGA output, but the voltage levels above were not encouraging."
For more information, Verbeure turned to a copy of the Sony display service manual — provided on microfiche and read, in the absence of a dedicated reader, through a microscope before switching to a library scanner to better view the document's schematics.
An initial attempt to connect a VGA port to the display's rather wasteful 40-pin connector, however, failed — simply because the 20Mhz pixel clock required to match the monitor's expected input was too low for the laptop on test. Experimenting with a higher-resolution image brought up a visible picture, squeezed horizontally but recognizable — and a test bitmap showed that, with some clever processing of the image before output, the display could serve perfectly as a monitor for a compact arcade cabinet.
More details, including the use of a suitable power supply so the Sony monitor can be used outside the HP logic analyzer, are available on Verbeure's blog — where updates on the project, which still requires Verbeure to "build a case, PCBs, give the power supply circuitry and disassembled Pano PCBs a place, and so forth," will be posted when available.