I have the same problem with the MS4622B. But my device was not completely dead from the beginning.
In the first step the bootloader started normally. It tried to load the application program from the floppy first, then from the internal hard disk and then successfully from NVRAM. Then he started the application program with the corresponding message.
But then nothing happened anymore. First I thought that the program image was defective and started the internal debugger of the bootloader (after power on press "1"). With the help of this debugger I was able to reload the application program from diskette into NVRAM. But there was no change.
Since the behavior corresponded exactly to what happens when you enter a non-existent Internet address as default gateway when configuring the Ethernet interface (software bug documented by Anritsu), I suspected that some bits in the BBRam, which I assume will store this configuration, might have tilted.
So I measured the voltage of the BBRam's battery without removing it from the BBRam and see, the voltage was only about 500mV.
When I then restarted the device, it remained completely inactive as in the cases described here (keyboard LEDs all on). I don't know how you can discharge a battery with a voltmeter with 10Megohm internal resistance, but obviously this was the case. The battery can't have been lifted by the probes either, because it's clipped firmly onto the ram.
If it turns out that the internet addresses are stored in the BBRam and the bits are tilted, then this would mean that the bootloader does not check the integrity of the BBRam's data via a checksum, but via a magic number. At least a program cannot read the battery voltage according to the data sheet of the BBRam.
The next question is, what is stored in the BBRam at all? Because the calibration routines mentioned in the manual, such as the user calibration, the ALC calibration and the receiver calibration, are stored in files on the internal hard disk. Only the DAC value for setting the 10MHz fundamental frequency is stored there according to the manual.
Thus, basic data seems to be stored there, such as other DAC values or also e.g. the activation of options as well as the address of the GPIB interface etc..
I suppose, therefore, that the whole device will be adjusted after a data loss as well as after production. This will probably be done by a program, which Anritsu owns for this purpose, but probably did not make available to the public.
Possibly this program is on the boot utility disk that comes with every device. Unfortunately I don't have it and I don't know any documentation about it.
Anyway, it's not enough to patch the bootloader so that it doesn't test the BBRam, although that would be very helpful, because you can run any program that the bootloader finds under A:\SYSTEM\APP.
Is there anyone here who has ever contacted Anritsu about this issue?
Greetings Dieter