Harman Kardon PM655 Protection Schematic

[Cortez]

Hi!

I'll get a blown HK amplifier soon to repair and I'm on the preparation phase so I checked the schematic, and the protection part in focus.
Here is the schematic which is 90%-ly clear, but I can't understand the Q4 section... 🙄
Could you help me what the purpose could be?
I also simulated it in LT but still not clear.

So far the sections I understand:

1. on the left Q401 + 2 FETs: they mute the input stages
2. the top-right: is the PS for the protection (D3, D4, C10 etc)
3. R5 + C11: forms the "power on delay"
4. Q2 + Q3: protection latch config with some "+" FB (via R8)
5. Q8 + Q7 + Q1: the overcurrent detection
   (Q8 base gots a positive voltage when there is ovvercurrent situation which shunts C11 finally)

But what this Q4 + D5 + R16 are doing..?

Thanks in advance!

PS: In the simulation I increased C10 to 100uF as with 4u7 I got "heavy" ripple ot the "-4.8V" line.