Hey folks, I hope somebody would help me with the issue I encountered with my two autonomous Voltronic inverters.

A friend of mine sent me this firmware and I followed the guide for flashing MCU & DSP.
MCU flashed successfully, but DSP flashing couldn't succeed.

From WatchTower:
Main CPU firmware version: 00045.04
Secondary CPU firmware version: 00012.28

The dsp 245.11 .exe firstly argued that it couldn't open COM port.
COM port is OK, I am using the same USB-RS232 adapter to flash other inverters and two Xpert Max 7.2 KW got MCU flashed with it. WatchTower opens port as well.

Then I tried to put patched "dsp.hex" inside Remote Panel Reflash folder from where I managed to flash MCU and press Update DSP.

Inverter's display went off and didn't get back to on state until I reflashed MCU again.

How can DSP be flashed without the risk of bricking of these inverters?
Thank you in advance!

dsp 245.11 patched Max 7.2kW '2809 120V.zip Remote Panel_Reflash_MCU(12.28).zip

On 2026/05/27 at 6:26 AM, SuperMaximus said:

How can DSP be flashed without the risk of bricking of these inverters?

It's possible that you need the resistor in the serial cable, details in this post. I'm afraid that I don't understand this issue at all.

It's also possible that the opto couplers in your display and/or inside the inverter are getting old and slow; they do apparently deteriorate with age. Maybe the DSP firmware is larger or the flash firmware is somehow more demanding of time, or the fact that it has to go through the display has something to do with it.

On 2026/05/27 at 6:26 AM, SuperMaximus said:

Inverter's display went off and didn't get back to on state until I reflashed MCU again.

That's pretty weird, though I guess it fits best with the slow opto coupler theory. Though normal operation is at 2400 bps, while reflashing is at 9600 bps, so even if the optos are marginal at 9600 bps,, once you get through a firmware update they should be fine.

Could it be noise from the PV wiring? Were you flashing during the day with the PV connected when you had problems? If so, you might need the capacitor mod, though this usually affects only the display.

@Coulomb

I would probably think of resistor like you proposed if my MCU wouldn't get flashed successfully. But it was flashed normally using the same cable and then I tried to do the same with DSP. I have 2 inverters of the same model and I tried flashing both. One has no PV connection at all, functioning as battery<->grid only, another one has 1 MPPT connection.
I didn't try with 2400 bps, but 9600 / 19200 gave me no luck.

I flashed another inverter's MCU/DSP (Voltronic Axpert MAX II 11K Twin / Axpert MAX E Duplex 11KW) with the same cable/adapter another day and it went well.

Will be grateful for any help!

20 minutes ago, SuperMaximus said:

I didn't try with 2400 bps, but 9600 / 19200 gave me no luck.

The bit rate is fixed by the firmware; the reflash tool ignores any speed settings in Windows.

21 minutes ago, SuperMaximus said:

I flashed another inverter's MCU/DSP (Voltronic Axpert MAX II 11K Twin / Axpert MAX E Duplex 11KW) with the same cable/adapter another day and it went well.

So that indicates that your serial to USB adapter, PC etc are all working fine.

So the problem has to be with that particular inverter. Is it possible to swap displays to see if the problem is in the display or the inverter proper? There may be problems with Twin versus non-Twin, Duplex versus non-Duplex etc.