Re: Hi From London England
Posted: Mon Jan 06, 2020 1:12 am
From the above ROM swapping tests above I had the impression the lower ROM was faulty so today I installed a Universal programmer I bought a few months ago to test the chips. After jumping through hoops on Windows 10 I managed to get it working but I searched the data base for the ROM type and couldn't find the 23256 or 23128 numbers. I assumed they are OTP types so I used the 27256 type that is not an OTP but should be pin compatible. The lower ROM shows gives pin faults on the five pins 15 to 19 and the upper ROM passes the pin test but I can't read either of the ROMs. The pin fault stops the 23256 from being read and the read chip ID prevents the 23128. I might be doing something stupid with the type selection but I think the chips have the same pins and the five that give a pin error are the lower five of the data bus that is the same on both chips so it does look like the 23256 is faulty. It is annoying that I can't read the 23128 chip either for a different reason that I can't fathom. Of course it might that I just don't know how to work the programmer yet and I am doing something stupid.