Is my TI-58C hosed?

[Paul Berger (Canada)]

Hmmm well now that I actually look at the board in a 58C I see that they are in fact quite different in layout, it would seem the service guide is referring to the earlier TI-58 that did not have continuous memory, so the one you see is likely the only RAM chip. I have 2 58Cs here and the board layout in the two is quite different, one I think is likely the same as yours as it has the same TC5047 RAM chip in it, the other would seem to be a slightly older one going by the date codes on the the chips and it has a house number 18 pin chip for RAM and the CD2400 and CD2401 are stacked . Since the TC5047 is a regular 1Kx4 SRAM chip with separate 10 bit parallel address bus and 4 bit data bus additional logic would be required to interface it to the processor and it seems that the TMC0591 that is immediately below it provides that function. The regular pattern like you are seeing might be an address issue such a a hot bit on the address bus or it could also indicate an internal problem with the RAM chip such as a defective row or column in the array of memory cells.