Peter Sam

Today I tried upgrading the 7.2KW with the 90.19 firmware you provided and it doesn't report an error now. Thank you God for arranging all this and allowing me to solve a problem that has puzzled me for a long time here. Thank you for your patience and enthusiasm. I'll have it installed tomorrow and try to get it working, hopefully the good news continues. Greetings from Korea. @Coulomb @Georg594  @Steve87 

Hey @Peter Sam, I have a customer out in the middle of the Free State with the same issue... As mentioned by @Coulomb, the master of software issues, it's an EEPROM issue and an update/patch will be needed to fix it. If your supplier has contact with Voltronic they can get a custom package made but they need to be written specifically for each serial number or you'll run into further issues down the line. Apparently, as per Voltronic, this is caused by a litany of things from sudden shutdown to a random hiccup...
So if you don't come right, since some of these fixes can be rough to execute correctly, your supplier can just give Voltronic the "F90" error code and serial number to get a custom package written for your unit. They may be slow and difficult to deal with but there is less room for error, I have tried this before and ended up messing it up... xD

@Peter Sam, note that this firmware works around the issue, but there may be an underlying issue with EEPROM access. If so, you may find settings being forgotten, measurements off, serial number not matching label, and more subtle and important issues. If so, you may need to get it repaired and/or have a custom setserial  command made for you to initialise the EEPROM correctly (assuming it just got scrambled, yet the hardware is otherwise fine).
Dodgy EEPROM can be a real hassle.

Good to know that the Voltronics banner & the solar bug has hit as far afield as Korea. Enjoy the machine, glad you got it fixed!!!

Today I tried upgrading the 7.2KW with the 90.19 firmware you provided and it doesn't report an error now. Thank you God for arranging all this and allowing me to solve a problem that has puzzled me for a long time here. Thank you for your patience and enthusiasm. I'll have it installed tomorrow and try to get it working, hopefully the good news continues. Greetings from Korea. @Coulomb @Georg594  @Steve87 

감사합니다

@Peter Sam, I can confirm that the attached zip file contains main firmware for Axpert Max 1 7.2kW version 90.19, patched to avoid fault code 90, and with Georg's patches to avoid the worst of the "stuck at 90V" MPPT problem, with 120 V minimum MPPT voltage.
Assuming that you have a '2809 processor (probably with original firmware version 45.xx), this will solve your problem.
The fault code 90 is a brutal way to punish owners who buy cheap clones that use illegal copies of Voltronics' firmware, but it also catches out some legitimate Voltronic owners, who have an EEPROM glitch, or some other glitch. It only shows up after 60 days of runtime.
Edit: I'm not aware of any 7.2 kW models with the newer '28066 processor, but if you do happen to have one, then the new firmware will refuse to load, but you should not brick your inverter.

Then you should return this unit to the seller because it's defective on delivery. F90 is not a normal fault. 

F90 is a " clone " detection but sometimes just a corrupt eeprom.
 
The firmware is based on 90.19 and shows this too.
It has F90 patch applied and mppt optimized like in my 8kw firmware ( these versions are nearly the same)

F90, Is a fault from a bricked inverter. Somehow, you now have to try to salvage & get this machine working again by trying to flash new firmware or older compatible firmware. Why did you try to flash firmware in the 1st place. It's a very unforgiving task if it goes wrong like this. 
What was your original problem to flash, what were you trying to improve?