Have you exhausted the advice in the FAQ.
https://www.volvoclub.org.uk/faq/Ele...struments.html
https://www.volvoclub.org.uk/faq/Ele...eterRepair.htm
If you are able to narrow it down to the actual instrument then the second link will help you or the electronics engineer of your choice to repair it.
Be aware that some versions of the FAQ highlight the wrong screw to undo to dismantle the cluster. If it doesn't come apart very easily don't force it but investigate near the screw which you've just undone that looks slightly different to all the others.