A short circuit of additional diodes can be checked without removing and disassembling the generator. As well as for checking the diodes of the rectifier unit, in this case it is necessary to disconnect the wires from the battery and the generator and wire 5 from the output "IN" voltage regulator (see subsection 12.13).
"Plus" batteries through the lamp (1-3W, 12V) attach to output "61" generator, and "minus" to one of the rectifier unit mounting bolts.
If the lamp lights up, then there is a short circuit in one of the additional diodes. You can find a damaged diode only by removing the rectifier unit and checking each diode individually.
An open in additional diodes can be detected with an oscilloscope by distorting the voltage curve on the plug "61", as well as low voltage (below 14 V) on plug "61" at an average frequency of rotation of the generator rotor.