HP97 memory problem

[teenix]

If you add any program steps up to step 33, then most times step 29 is 51 regardless of what was entered.

When this occurs, what happens if you BST to program step 28 and then start inserting five more program steps - say [2] [2] [2] [2] [2]. Does the 51 move to the next step, and there is only one 51 still in the program, or does the program code in step 29 and beyond change to 51's also.

Code:



Normal          Problem_1        Problem_2       Problem_3

step code       step code        step code       step code

27   1          27   1           27   1          27   1
28   2          28   2           28   2          28   2      <<< start inserting 2's
29   3          29   51          29   2          29   51
30   4          30   4           30   2          30   51
31   5          31   5           31   2          31   51
32   6          32   6           32   2          32   51
33   7          33   7           33   51         33   51

Problem_2 would indicate that a "new" step caused Problem_1 but the RAM is ok.'

Problem_3 would indicate a RAM issue because step 28 was supposed to carry to step 29, but instead 51 still appeared. If this is the case then the code for R/S is 0, so it probably means that the RAM at step 29 is faulty and cannot be written to and stays 0. (sometimes)

Still, this doesn't explain why a card read works, unless sometimes it doesn't.

Either way if would appear that a ROM/RAM IC is starting to fail. If RAM then the IC marked 1818-0229 could be faulty. If ROM, it would be hard to track down unless you could analyze the code flow with a storage oscilloscope.

Maybe replacing the filter capacitors in the power supply might help - just a guess.

cheers

Tony