Hi Neil
The lcd display failing is a very common problem with Volvo Penta tachometers. The display just fades away to nothing. However, the engine hours are still being counted and stored on a chip in the unit.
Below is a copy of a post I made in 2021 when I finally got round to replacing the lcd display on our boat.
It was fairly easy to do and the display is still going strong 3 years later so it has outlasted the original Volvo one already.
Good luck
Andrew
The engine hour meter on our 36 C (VP2030) failed a few years ago which is a very common fault. Finally, got round to repairing it by replacing the faulty LCD screen. The actually hours are stored on a separate chip within the tachometer so continue to record even when the display is not working. http://www.akspeedo.com sell the relevant screen (VDO LCD Pixel Repair) at £21.99 which is a lot cheaper than a new tacho. Received it the next day so very good service. There is a link to a YouTube video on how to do it but even I found it fairly easy, taking 40 minutes in total. Just make a note of how the bezel sealing rings come apart to put them back the right way and I had to power up the unit before reassembling the tacho needle to get it to point at zero. Not sure how long the replacement LCD screen will last but appears to be better made than the original.