Help diagnosing a IBM 5140 Convertible

[nestor]

I have a IBM Convertible 5140 that behaves this way:

After power switch is pressed, it produces a continuous beep and nothing more. Watching other 5140 videos on youtube, it seems that this beep should be very short. Disassembling the BIOS I saw that between the beep on and the beep off instructions there are some test operations.

I modified the BIOS to produce a changing beep, and it is produced without problems:

What do you think I should do next?

 

[modem7]

Disassembling the BIOS I saw that between the beep on and the beep off instructions there are some test operations.

What do you think I should do next?

One of those "test operations" may be to validate the checksum of the two BIOS ROMs. Does the content of your two ROMs match the two 5140 ROM images at http://members.dodo.com.au/~slappanel555/rom/rom.htm ?

Note: There was only one BIOS revision for the 5140, one dated 13SEP85, and so the comparison is valid.

 

[nestor]

Does the content of your two ROMs match the two 5140 ROM images at http://members.dodo.com.au/~slappanel555/rom/rom.htm ?

The contents of the eproms are exactly those two images you provided. I burned them because the original mask roms behave the same way, so it is not a firmware problem.