Hi,
I recently picked up the hobby of ( trying to ) repairing old test equipment and got a TDS540.
I have been trying to get it to boot up but it is stuck with a flashrom checksum error.
It seems somehow the firmware got compromised.
All caps have been replaced and the boards ( A10, A11, display ) look good with no apparent visual damage.
NVRAM has been replaced with a preprogrammed version from kellyjo_13 / ebay.
After reading to multiple posts on different forums I guess I am more confused than before...
My questions are :
Where can I download a working firmware version for my TDS540 ?
How to update the FW ( in Windows ? , DOS ? )
Which ( if any ) GPIB to USB converter would work or do I need an old 488.2 card ?

The boot message looks as follows :
Enabling Bus Control register. Value = 0x67
IMR 1 Register test passed.
Misc. Register test passed.
Timer Interrupt test (Auto-Vector) passed.
NVRam DSACK test passed.
NVRam Write protected.
Flashrom DSACK and JumpCode test passed.
Invalid Flashrom Header checksum = 0x3efc, should be 0xfefb
Flashrom Checksum test failed.
Cannot transfer control to Flashrom.
Transferring control to the SDM (monitor).

Any help is very much appreciated.

Hans