After replacing the backup battery I recommend to reset the BM6500 via the servicemode. All settings will go to default, like bass, treble, etc.
After that, check whether the displayed frequency is still wrong. If it is, you can perform a FM display setting. You need a MCP or Beolink 1000 for that.
These procedures are described step by step in the servicemanual.  

rrm wrote:

My BM6500 has been recapped including replacement of the CPU's backup battery. After the repair the FM frequencies displayed on the two-way remote are slightly off, and if using direct entry of the frequencies, correction is also required. The topic is mentioned in previous threads, and I have consulted the service manual, but am in doubt whether the adjustment can be done via 'Test Mode' and MCP6500 alone or whether it requires special equipment connected to the antenna input. Thanks if you can explain the steps to go through to adjust the FM frequency display.

As Beobuddy wrote, it can be done with the service menu. It is easiest to use a Beolink 1000 for this.

From standby, press RADIO -> GOTO and then tune with the STEP UP/DOWN to a station you know the frequency of, and verify that LOCKED is lit up. Then short-circuit briefly, the test-point 2 times after each other, then press GOTO and the frequency you have tuned to, f.eks 9-2-3 for 92.3mhz. Then press STORE. If everything is fine, it will display a 4 in the display, if not, 5 will be displayed. 

Verify with the MCP that the frequency is now correct.

/Weebyx

Thank you both for the instructions. Is the solder point to short-circuit (4TP1) accessible through a hole in the CPU's metal shield? Which tool should be used to perform the short-circuit?