Unable to program CPLD or blank screen

If you are sure your soldering is correct, the most likely cause is that the CPLD already has some other firmware programmed into it. This can either result in a programming failure if the CPLD recovery menu is displayed or just a blank screen with no menu. In the latter case holding down all 3 buttons during power up or reset will display the CPLD recovery menu and you can try reprogramming but that will probably fail.

To recover from this, cut the three solder jumpers JP1, JP2 and JP4, reprogram the CPLD (holding 3 buttons to get to the menu if necessary) then remake the jumpers with solder blobs.

Note for Amiga CPLD boards these jumpers may have been omitted making such recovery much harder although you can get the equivalent by desoldering and lifting up pins 6, 7, and 44 of the CPLD. Also such boards usually only have one button preventing use of the three button recovery menu option.
To work around this you can delete the file 'Delete_This_File_To_Erase_CPLD.txt' in the '/cpld_firmware' folder on the SD card. On the next bootup the software will try to erase the CPLD and as long as the pins are disconnected that should work.

The general Amiga recovery procedure is as follows:
First delete 'Delete_This_File_To_Erase_CPLD.txt' and reboot
If you are lucky the CPLD might get erased without any hardware changes but if that doesn't work
Cut JP1, JP2 JP4 (or lift CPLD pins 6, 7, 44)
Then delete 'Delete_This_File_To_Erase_CPLD.txt' again and reboot
The file gets re-created after every reboot so you have to keep deleting it to keep trying to erase
Remake the jumpers or resolder the pins.

No video output on first startup with a new monitor when using a 50Hz (PAL/European) computer

Try holding down the menu button (SW1) on power up/reset until you get a video output, (may take 5-10 seconds). If this works it means that your monitor supports 50Hz but doesn't like the auto selected resolution. Holding SW1 down during startup forces the output to 60Hz so you can change the menu settings. Try manually selecting other resolutions like 1920x1080 or 1280x720 as they have a better chance of working at 50Hz. If all else fails you can change the refresh to 60Hz but that is less than optimal as it means there will be judder on any motion with 50Hz computers.

Noisy / flickering pixels

When setup correctly, the output of RGBtoHDMI should be completely noise free and any flickering pixels usually means that an adjustment in the sampling menu is required which will generally only need to be done once for any particular machine. If you are regularly switching between machines that share the same profile but require different settings then it would be better to create separate profiles for each machine by making renamed copies of the existing profile .txt file or folder in the Profiles folder on the SD card.

For both digital (TTL) and analog sources, the first thing to try is an Auto calibration of the sampling phase.
This can be done using the option on the main menu or holding SW3 (hold until it starts).

You can also manually adjust the sampling phase in the sampling menu and that should be adjusted to eliminate or minimise noise.

If you are using the analog interface the next option to try is manually adjusting the DAC settings in the sampling menu which set the level slice values for the 1 bit A to D converters (these are not altered by the auto calibration). Try adjusting each of the YUV or RGB levels as appropriate a few values in either direction to see if it improves things. (leave each one at it's original value if it doesn't)

After making any changes don't forget to use the Save Configuration option in the main menu to keep those changes

Teletext Mode 7 on the BBC Micro

This is the most difficult source to sample as the 6 Mhz teletext pixel clock is generated in an unusual way from the 16 Mhz master crystal which involves resistor/capacitor filters and this results in the pixel clock being very asymmetric with the amount of asymmetry varying from machine to machine.
If you only get problems with certain combinations of foreground & background colours you should always try running the Auto calibration with those being displayed.

This is a test ssd which displays all possible combinations of foreground and background colours and all the problem characters

Again manual adjustment should also be tried and there are additional adjustable phases A-F to cope with the asymmetry. Finally try manually setting the clock multiplier to x16 in the sampling menu before calibration or manual adjustment but x16 might not work as it overclocks the CPLD so you could end up with a blank screen, streaking or a very noisy image with that setting.

If you are unable to completely resolve any mode 7 noise issues by making the above adjustments then you can try the following hardware changes:

1. Reduce the length of the BBC video cable to 30cm if it is significantly longer than that.

2. If you are connecting to a BBC micro or Master 128 via the analog board, try a direct digital connection instead as some of the very narrow pixels resulting from an asymmetric clock can exceed the input bandwidth of the analog board.

3. Adjust the values of the resistors/capacitors in the 6Mhz clock circuit on the BBC to make the clock more symmetric.
   For further details of this modification, see this page: Mode-7-Clock-Modification.

Screen flashing on and off

This indicates that the source input timing doesn't match the profile and you will often get this when the wrong profile is selected but it can also happen with some machines that have a programmable CRT controller which some software (e.g. demos) has reprogrammed to output a non standard signal. You will need to create a new profile to display such a source (see page on creating a new profile). If you end up with multiple profiles for a computer you can replace the original single profile with a folder instead and put the multiple profiles in that folder. The software should automatically select the correct profile corresponding to the source timing as long as there is sufficent difference in the hsync frequency, number of lines or sync polarity. (see examples in the profiles folder on the SD card)

Screen blanking during mode changes

On some computers like the BBC micro or PC, When the video mode changes, the hdmi output has to be re-genlocked to the computer's video due to the sync disturbance. If your monitor doesn't like the speed at which the genlock is changing the hdmi clock it will blank the screen during this process but there is an option in the settings menu to help with this: Go to the settings menu and change "Genlock speed" to Slow or Medium (It defaults to Fast) then save configuration (use the highest speed that works).

Auto NTSC artifact switching on Apple II

If the auto NTSC artifact detection isn't working on the Apple II, try adjusting the Y Lo setting in the sampling menu as that sets the level of the colour burst detection.