If the error code doesn't change after all of that troubleshooting, then it's very likely the MB.  Can't say for sure the MB since can't diagnose from here.

It's rare a CPU goes out.

RAM sometimes goes, but then error code would change once removing it.  I think with it removed, you'd get some beeps.  One could try a stick of new RAM just to make sure, or try a stick at a time of the current RAM to see if error code changes.  It might like beating a brick though.

Good troubleshooting by the way.

Replace the coin cell battery and clear CMOS.

Which I should've thought of first as usual.

@Chino de Oro​ 

Hi Chino,

Battery changed and CMOS cleared. No success. Amber led continues to blink 2 then 3 time.

Is there a way to be sure 100% that is the MB? 

Thanks.

If you tested with known good components and there is no sign of life, the board is faulty (dead).

Sometimes, disclosing the event leading to system failure may help with troubleshooting suggestions and inputs.  For testing, just use one CPU and one stick of RAM.  If the issue is persisted, consider motherboard replacement.

A used replacement board starts at $50 USD.  A barebone system starts at $100 USD