ICOM IC-745, LSB mode

[Zolive974]

Hello,

I have a little problem with an IC-745 which prevents me from going to LSB mode, let me explain:

Initially the radio was sold for parts as non-functional, I managed to repair it by flashing the SRAM module (thanks to your forum)  and performing an alignment using the service manual.
The radio works well on all bands and I can listen when there is modulation on the bands.
However, when I press the "MODE-SEL" button to change modes, it works fine and I have in order "USB, CW, RTTY, AM, FM" and normally, pressing again this same button, I should reach LSB mode, but impossible, it automatically brings me back to USB mode, and so on, I cannot access LSB mode.

The only way to enter LSB mode is to press the "VFO A/B" button in order to switch to VFO B which at the moment is magically set to LSB.
On this VFO B I can therefore go in all bands (from 0 to 30Mhz) in LSB only, and if I press the "MODE-SEL" button nothing happens, I remain stuck in LSB mode.

To return to the other modes, you have to switch to VFO A, but once there I would have access to all the other modes except LSB.

Do you have any idea of ​​the origin of this problem?
I searched a bit on the internet and it seems that it might be a fault in the SRAM module but not much information on this subject.

Knowing that I do not have another replacement SRAM module to test, I am therefore turning to you to guide me in researching this problem.

Thanks for your help.