Your test does seem to rule out contacts. On my 2100P contacts were a huge problem - not just the contacts you can see but also the contacts on the other side of the contact block. Printers are a pain.
> I got an Epson DX7450 second hand. It came with no cartridges, so I bought a CIS system on Ebay with autoreset chips. However it does not recognize the black cartridge no mather what I do.
> They even sent me a spare chip for the cartridge but it did not help either. Any idea what should I do?
> It is not the contacts, because when I swap the black and yellow cartridge it shows that yellow cartridge is not recognized.