C215 CL500 - Instrument cluster lights

[Johnny 89]

I have a C215 where recently the instrument cluster lights have stopped working.

One day they came back non while driving but went off again a few days later. Sometimes they partially work.

I've checked the fuses under the bonnet and did a reset by disconnecting the negative terminal for 15 mins. Unfortunately no difference.

Google would have me believe it's likely an internal board failure (voltage regulator or backlight inverter). Has this happened to anyone else and how was it solved?

Thanks.