SDG #365 Reverse Engineering NAD D7050 OLED Replacement for IPS TFT

This episode returns to the NAD D 7050 amplifier repaired two videos earlier, which works apart from its failed front panel OLED. The original 1.5 inch 128 x 128 panel uses an SSD1355 controller that is no longer available, and the obtainable SSD1351 panel differs in registers and initialisation. With no way to modify the front panel firmware, a microcontroller must sit between the amplifier and a new display, which also allows a TFT to be used, avoiding OLED burn in.

A Saleae logic analyser captured the power up, splash screen, a volume change and power down. The display is driven by one way four wire SPI with a data/command line, and a Python script decodes the command stream against the SSD1355 command table: configuration, a gamma lookup table, then repeated memory writes of 32,768 bytes, a full frame on every update. A second script extracts those frames into images, confirming the logo, input and volume screens, and showing the content is monochrome and storable at one bit per pixel. Rotation is handled by the amplifier sending a 0x36 memory access control command rather than re-sending the data.

With a 16 MHz SPI clock and 32 kB per frame, the receiver needs slave SPI with chip select used for frame synchronisation, so a dual core dsPIC board was used. The firmware was proven with an Aardvark SPI adapter, then on the amplifier, detecting the 0x2C RAM write command and buffering pixel data. Relaying the frames to the SSD1351 OLED worked, and a driver for a 1.8 inch 128 x 160 TFT worked better still, with real time pixel remapping for orientation and the backlight blanked when the amplifier is off. The next step is a replacement front panel PCB with the TFT behind the existing square window.