This is my first writing :)
I have installed Nakamichi NA-1550 in my car and found a problem about mic sensitivity of the bluetooth phone connection.
I've been googling around and finally found this link https://tdj.com.au/firmware/Nakamichi/NA1550/ and try it.
Let's do it ;)
Step 1: Things We Need
1. The Head unit ( LOL )
2. Computer or anything that can do the downloads and copying
3. Firmware files from https://tdj.com.au/firmware/Nakamichi/NA1550/ and download all and put in one folder then extract.
4. Two USB drive because the process cannot be done with two files in one drive.
5. Copy TF21K.BIN (extracted from NA1550A_DvD Servo_140805.rar) to the first USB drive.
6. Copy TF21MCU.BIN (extracted from NA1550 MCU SW 20150202.0.rar) to the second USB drive.
Attention : Never pull the USB drive or power off the unit while upgrade on progress!
P.S : Read NA1550 SW UPGRADE PROCEDURE S 140508.doc for full documentation.
Step 2: Upgrade #1
Install first USB to the unit, upgrade display will be shown, no need to press any button, and will upgrade automatically about 5-6 seconds.
When upgrade finished, it will switched to tuner mode.
Step 3: Upgrade #2
Install the second USB to the unit, press “OK” Key on the unit, or “OK” key of remote while upgrade UI displayed.
Display will be in black screen and light blinks untill upgrade completed, Unit will rebooted after about 2 minutes and will be in tuner state with factory default, we'll need to adjust everything again.
Step 4: Finished
That's all...my unit is upgraded and I will tested later :)