The carriage board buffers the printhead data drives the printhead and the Z-axis motor (carriage height), monitor the ink levels and reservoir temperature and drives the ink reservoir heater triac. If it fails during the initialization, it seems that the problem is with the board itself.
First of all: check the D9 LED diode - if it's on, the 36 V voltage is delivered to the board. If it's off, check the power supply hidden at the back of the carriage.
D20 LED diode is a so-called 'heartbeat' diode - if it flashes twice per second, everything is ok. If it's constantly ON or OFF or pulsing once per 4 seconds, something is wrong with the board. Pulsing once per 4 seconds means that don't receive the data from the motherboard. Constant ON means that the communication was lost after the initialization (I don't think this is the case). Constant OFF means that one of the power supply voltages generated by the board is missing (the board generates separate voltages of 1.5, 2.5, 3.3 and 5 V).
In old machines, these boards may suffer from the ink mist inside the carriage, so I wouldn't be surprised that it's broken...