sundewzer wrote:... I guess easy come easy go...
And it takes only a few seconds.
Unfortunately, you are just getting started! There are almost a dozen additional schematics that you must study and examine their related components. The one you found is "schematic1". Search also for: schematic2, schematic3, schematic4, ...schematicN, in which 1 =< N =< 12. Schematic12 was not entirely drawn, many pages would be required to show it all, but fractional parts did get posted.
When dealing with this reverse-current scenario it is very important to recognize that all five motor drivers, and the speaker too, have their driver xstrs protected by diode pairs connected from VBATT-to-xstr_base-to-SYSRTN, and ordinarily handle fly-back voltage generated when a motor is shut off. All those diodes become FWD biased under the reverse-current situation. Many become over stressed by the heavy surge current; and, that heavy current is collected and passed through the master, system-current shunt resistance provided by R148//R184 (which can be seen in schematic1, Zone-A3). Those resistors probably no longer have their original low value of resistance.
Generally, an owner is much better off to simply buy a replacement mobo, rather than go through the agony of repairing / verifying all sub-circuits!