Symptom:
When the ZX Spectrum with ZX-HD is powered on, and the HDMI output says to press RESET, and you press RESET, you only get a ‘test screen’ with vertical coloured bars.
The blue power led lights up.
Probable cause and solution:
The edge connnector of the ZX Spectrum might be dirty.
Clean it with IPA (Isopropyl Alcohol) and a cotton swab until no dirt comes off anymore.
Symptom:
When the computer with ZX-HD is powered on, the TV shows a black screen only, as if there is no input.
The blue power led lights up.
Probable cause and solution:
Power off the system, remove the 4 screws of the ZX-HD and take off the backplate.
Now power on the system and check if the led at the bottom of the Raspberry Pi Zero flashes.
If not, there may be a problem with the micro SD card: check the micro SD card.
If it Raspberry Pi Zero led does flash, the Raspberry Pi seems to boot but there is no output or the TV doesn’t accept the input signal.
In that case, test the ZX-HD on another TV.
The Raspberry Pi in the ZX-HD should negotiate a working resolution with the TV and automatically upscales the resolution to get sharp pixels, as much as possible with the TV.
However some HDMI switch boxes may cause problems with the negotiation, so test the ZX-HD without such switch boxes or other equipment in between.