(a) Upon default, when the damages are to be assessed, the court may hear the evidence and assess the damages without a jury for that purpose. If interlocutory judgment is entered in an action brought upon a penal bond, or upon any instrument in writing, for the payment of money only, and the damages rest in computation, the court may refer the matter to the clerk, to assess and report the damages, and may enter judgment therefor. However, either party may have the damages assessed by a jury.
     (b) Unless a jury has been waived, the trial court shall empanel a jury to assess damages: (1) if the ruling on a post-trial motion is in favor of a party entitled to recover damages and there is no verdict assessing his or her damages; or (2) the reviewing court remands solely for the purpose of assessing damages.