Hi

I've had to repair instrument clusters in 740 850's and now a 940.
Odometer gears, Blown lights, and cold solder joints on the PCB flex cards.
Do you have the Volvo wiring diagram/fault tracing manual for your model year?
Or provide a link to it on line, It should be easy to repair.

How difficult is it to get the cluster out to work on?
From the sounds of it you have a bad solder joint or loose connector pin in the instrument cluster PCB in the +12VDC supply circuit.
With the cluster out, you will probe the 12vdc to find out where it gets lost and make the solder joint or faulty connector repair.

It should be easy to find if you have the Volvo wiring book.

My last adventure was with my 940 that had a chronic gas gauge dead that Volvo never could repair. They replaced the meter assembly but not the entire instrument cluster.
It was a nasty intermittent failure and finally was resolved
by soldering a jumper on the plastic Yazaki PCB where the +12VDC track went to the back side for 1 inch and up top again. The joint failed on the back
side of the PCB.
I needed to add more vacuum line to the boost gauge to be able to pull the cluster out far enough and flip over to see the PCB and use the VOM to find
the fault.

You have to catch it when it's broken, is the secret.

Bill