I tried gemdos11-boot.dc in DiskCopy 6.3.3. It coplained, too, that the check sum is invalid and refused me, even thoug in "preferences" the "checksum verification" is not set. It told me the ckecksum it expects.
So I went back to my ubuntu box and hexedited the image file so that DiskCopy would...
I tried to make a floppy from the attached file gemdos11-boot.dc. I get an error in Disk Copy 4.2 when opening the file: "Checksums don't match. Image file is probsbly corrupted". Strangely, it does not say what is the expected and found check sums (I've seen it do that with other images). I am...
Answering myself:
It turns out this is a tiny amplifier for the video-out connector.
Has 2 transistors and few resistors and caps inside.
This component was made with discrete elements on the Lisa 2/5 motherboard; it's schematics can be seen on the "Composite Out" section of this diagram.
What is this yellow component on the Lisa 2/10 motherboard, can I find a replacement for it, or build one from discrete components?
It's located right behind the mouse connector.
Labeled "343-1003". Has 10 pins in one row. On the board it is labeled with white letters "U2".
Looks like a resistor...