You can repair MOS memory boards where the board is basically working, but just has some failing memory chips, without schematics. First you need to create a map which translates memory chip # to bits. You have 32 chips in the array, so there are probably 2 32KB banks, each 16 bits wide. Pull a chip, and then try and figure out which bit it is; then repeat with other chips to try and figure out which bits are stored in which chips. (Unless the designers were insane, each chip will hold the same bit in all the words in that bank.) On yours, the memory chips are in sockets, which makes this less painful. (On boards where the chips are soldered in, a program which loops, storing a word with a single 1 bit, can be used to the same effect; the chip data sheet will tell you which pin is the data pin.) Usually a missing chip results in bits stored in that chip reading as '0', but it's possible they will read back as 1. Anyway, to test the first possibility, start by finding a location in the each bank that can be written to all 0's and all 1's (read back after writing to verify). Next, pull a chip, and then try writing all 1's to that word in the low bank, and read it back. If it now has a 0 bit, congratulations i) you've verified that missing chips read as 0, ii) that chip is part of the low bank, and iii) the 0 bit tells you which bit that chip is - fill in that entry in your chip<->bit chart. If not, try the high bank word, and see if it now has a 0 bit. If not, try writing 0's to the high and low words, and check for a '1' bit; if so, i) missing chips read as 1, etc. If neither is true, check back here! Otherwise, try pulling another chip, and work out which bit that one is, and add it to the chart. Repeat for all 32 chips - although if you're lucky, after a couple you might find a pattern, and be able to predict which chips hold which bits. (But not always; many are random; see e.g.: http://gunkies.org/wiki/Q-RAM_11 http://gunkies.org/wiki/NS23M for some.) If so, do a few spot tests of your predictions to make sure your pattern is correct. With the completed chart in hand, given a failing word (address and bad data), you can work out which chip is at fault, and replace it. Repeat for all memory errors. Noel