Is there any output on the serial console with Coreboot? There should have been a lot of it the first time when you got to VGA init.
The problem is, not even the monitor turns on, which indicates that there is no VGA init or VGA signal, using both chips. I'll check with a multimeter if there is any current on the pins.
has a pin of the socket or the flash been bent?
some pins of the original chip have been slightly bent, but I fixed them with a pliers before inserting. Unfortunately my plcc32 extractor is too big for that board, so the first time I used a screwdriver to extract the chip and after that I used some filament underneath the chip to plug it out.
I did not check the serial output yet; the only lifesign is the onboard network chip which establishes a link to my switch. But my guess is, that board is beyond repair, as the original bios doesn't work anymore, there is no beep signal, and no VGA signal. If there is anything new, I'll let you know. Thanks for your help so far.
Mark