Hello everyone,

I have read several posts in the forum about a patch for inverter firmware that fixes an MPPT problem. Specifically, the tracker gets stuck at a local maximum, meaning that the maximum possible PV power is not being achieved.

I am using the ISolar SV IV 5.6K. The TMS320F2809 DSP is installed.

Can the attached FW be patched so that the MPPT tracker does not get stuck?

Thank you for your help.

V74_01 DSP FW image.hex

On 2025/08/15 at 12:01 AM, solarMax said:

Can the attached FW be patched so that the MPPT tracker does not get stuck?

74.01 has not been patched, but the more recent 74.04 has. Patched firmware version 374.04 implements only the lowered current threshold. I've come to doing the "full set" of patches for later patched firmwares.

On 2025/08/15 at 12:01 AM, solarMax said:

Specifically, the tracker gets stuck at a local maximum, meaning that the maximum possible PV power is not being achieved.

It's still the original perturb and observe algorithm, but there is a special test for low PV power that they get wrong, so it gets stuck at the low MPPT voltage limit. You can try the above, and if you don't like it, you can revert to the original factory firmware version 74.04, or I guess use the hex file you posted.

Hi Coulomb,

Thank you very much. I will definitely try that and let you know how it goes.

Hello everyone,

Unfortunately, my attempt failed in a rather strange way. I operate three converters using parallel cards so that they form a three-phase network.

The update via the COM port worked without any problems for two of the three inverters. On the third, “UPG yes” appeared briefly on the display, as it did on the others. Then error F32 appeared and it was bricked.

Fortunately, I have the right JTAG adapter to revive the DSP board. So, without further ado, I installed your patched FW 74.04 via JTAG and the inverter started up again.

However, error code F99 now appears. I can't find a description of this anywhere. When I reinstall my old FW 74.01 via JTAG, the error does not appear and everything works normally.

Can you explain this? Especially since it only affects one of the three identical converters? Interestingly, it is not possible to install the update via the COM port, even after repeated attempts.

Thank you very much.

Edited August 28, 2025Aug 28 by solarMax

These are two unrelated problems. The update via COM port fails probably because of a weak/slow optocoupler or some other hardware problem which corrupts the data.

When uploading the firmware update via JTAG you get F99 which means "missing bootloader". That's expected. The firmware checks for a signature at the end of sector A where the bootloader resides. And it's not there because the firmware update does not contain the bootloader. When flashing via COM port, sector A is never erased or overwriten but the JTAG utility by default erases all sectors.

I've merged the patched firmware with part of your original file. This one should work if uploaded by JTAG. Do not use this with the original update utility.

dsp_374.04_patched_05_wboot.hex

16 hours ago, kuba.cz said:

These are two unrelated problems. The update via COM port fails probably because of a weak/slow optocoupler or some other hardware problem which corrupts the data.

Thanks for the clarification. It may well be that the inverters did not use the best optocouplers.

16 hours ago, kuba.cz said:

I've merged the patched firmware with part of your original file. This one should work if uploaded by JTAG. Do not use this with the original update utility.

Thank you very much for your support. I solved the problem in a similar way. I created a flash dump from one of the inverters where the update worked and flashed it onto the “defective” one. Now everything is working perfectly again.

I'm amazed and pleased that you didn't need a 128-bit password to unlock the firmware. On many other models you certainly do.