think is better to start checking motors, before strip parts appart.
it is possible that transistor/drive card could have been damaged again if have a short in motor or their power cables.
you may want to check:
1-motor terminals against its frame for shorts, brushes beeing seated in good shape on conmutator. motor cables against frame
have found cables rubbing on hoses (steel recovering) doing short circuit.
also check the big resistors(R312,R302) for a good terminal
contact.
If contactors come in, they are making contact (not losing voltage through their tips)