The circuit in front of you is different from the one in the referenced schematic, and may differ also from the concept thereof that exists in your mind–it’s important that the three be consistent. Among other things:
- There’s 5 FETs on the board, and 3 in the schematic.
- The anode of what seems likely to be D1 in the schematic appears to connect to circuit common instead of the FET drains. This could lead to an over-voltage condition during FET turn-off due to winding inductance.
- What’s presumably R1~R3 in your schematic appear to be 100 ohm resistances, rather than zero as described on the schematic. That’s likely excessive, and would contribute to excess switching losses.
- What’s presumably the added zener appears to have been installed at a common connection of R1~R3 and driver output rather than across gate and source directly, apparently putting 100 ohms between the zener and the gate(s), which would tend to negate it’s potential benefit.
It’s common for FETs to fail short-circuit, to a marginally higher resistance than their normal fully-enhanced Rds(on). This could easily cause a connected motor in a circuit such as this to appear to turn full-on, followed shortly thereafter by the failed FET self-disassembling as a consequence of excess power dissipation due to the fault current. It seems that the only FET in the images showing physical damage is the one nearest to the apparent connection point of the motor return lead. This is, perhaps, not entirely coincidental.
Watching the Vgs and Vds waveforms will go far towards getting a concrete idea of what’s going on.