The Finalization of the mod, and tests
At this point with the bare driver, it's a good point to do the firmware update. So, got online, retrieved TK's latest Anduril2 rev 579, dated 2020-10-19, updated my Win 10 based Atmel Studio 7 Anduril2 project with the updated files, and set up a new config file for the HK90. Used the Q8 hardware config file (same FET+1 w/switch AUX LED's), but used the ramping table from the Mateminco MF01S config file (high lumens)
These type of lights with a reflector retaining screw inside the driver cavity, you have to make the wires long enough at a minimum to be able to move the driver out of the way to get a screwdriver on the screw to loosen up the reflector. You can't start with de-soldering the wires on MCPCB because the reflector is locked down. So here's the new 18 AWG wires threaded up

Now the wires soldered with plenty of flux:

Then cleaned up (psst: notice anything wrong yet?):

Applied kapton tape to protect against possible ground outs on the reflector, and the copper washer placed with MX-4 coating on both sides:

Next is adding the copper plug/heatsink, MX-4 on contact surfaces:

Heatsink placed, reflector secured down with the screw (copper screw is shipped but coming from China), and screw also treated with MX-4:

The resistor change made the difference I was hoping for - brighter blue switch LED's:

Ok, doing the first power-on test, heard a slight crackle when the LED's blink in tightening up the battery carrier and first contact is made, hhmm. Then clicked ON the light -- Ooops! One LED is out, dead. Ouch! opened her up, removed the reflector, and noticed the problem:
- Stupid me, the bad LED has the Red/Black wires reversed! I know I checked this and somehow totally missed it! The pics above captured the mistake, and still didn't notice it! :FACEPALM:
Ok - hoping for no permanent damage, re-wired, re-assembled - LED is working and doesn't appear to have any side effects. So, test results:
- lumens start-30secs: 18500 - 15880 (Tom E @'s), 16320 - 14010 (maukka cal'ed)
- 737 kcd
So it's a bump but not much. Kind of expected this but still there's something holding it back. Then realized I didn't look thoroughly at the springs:

What is this? Ohh, looks like a quality outer spring, and double inners of very thin, very soft copper or copper clad, soldered on the top, but not the bottom -- they have to go... So:

Removed the dual inner springs, adding 20 AWG bypasses:


When re-installing the spring PCB, added NO-OX-ID on all contact surfaces of the brass screws - nice brass screws came on the stock light.
Now we about done with the mods I wanted to do, minus the copper reflector screw replacement.
Doing just a quick lumens and throw measure, I see about a 5.3% bump on the 40T's (solder tops), lumens (Tom E/maukka): 19480/17190 at start, throw: 785 kcd
Now for the ultimate test - solder topped 30T cells, fully charged:
- lumens start-30secs: 20500 - 17580 (Tom E @'s), 18090 - 15510 (maukka cal'ed)
- 820 kcd (1811 meters)
So I think what happened here is the FET and 18 AWG wire change didn't do much because the springs were still holding down the amps, so once they were bypassed, got a decent bump with all the mods combined. Now I'm not seeing/measuring benefits of the thermal improvements. At 30 seconds on turbo, the housing in the hot area gets pretty warm but still ok to hold in the hand.
In the Anduril config file, I add these settings:
#undef DEFAULT_THERM_CEIL
#define DEFAULT_THERM_CEIL 60 // from 45 -> 60
#define MAX_THERM_CEIL 90 // from 70 -> 90
#define USE_2C_MAX_TURBO
// Make standard mode default, not Simple mode
#define SIMPLE_UI_ACTIVE 0
So I'm bumping the thermal ceiling, make getting to turbo easier, and defaulting to the regular Anduril UI (not simple or muggle). So I cal'ed temp, and set the ceiling to 85C. Also had to tweak the voltage reading a little, using the config UI (new feature).
Overall pleased, and really really glad I didn't mess up an expensive LED 
