HP97 memory problem

[AlexG]

I got a HP97 some time ago. The printer is alive, so is the card reader. But there's a problem.

Sometimes (90% of cases) I cannot enter any value to the program register 29. It always keeps value 51. Which is really 51 and shifts to the neighboring registers when editing the program. However, when the program (from the standard pack) is read from a magnetic card this register is fine.

Is it known thing? Any ideas how to solve this problem?

[Duane Hess]

Not sure how to take this.

You're entering a program and the instruction you want to enter at step 29 is lost? i.e. step 29 remains R/S?

For example, suppose you enter a 36 step program. Is the program correct other than step 29 is a R/S?

[teenix]

It may be a ROM that is starting to fail.

Does this problem occur if you try to enter a shifted function like [f] [->P] (INT), [f] [8] (if Y = 0), or does it only occur on single key functions like [SIN], [LN], [+] for example?

These two processes use different ROM code. The card read uses different ROM code as well, which might explain why it works.

It doesn't seem to be a RAM issue because (except for this one problem) program entry/editing work, and the card read works.

cheers

Tony

[AlexG]

(05-06-2023 08:59 PM)Duane Hess Wrote:  Not sure how to take this.

You're entering a program and the instruction you want to enter at step 29 is lost? i.e. step 29 remains R/S?

For example, suppose you enter a 36 step program. Is the program correct other than step 29 is a R/S?

Yes, exactly.

[AlexG]

(05-07-2023 12:03 AM)teenix Wrote:  Does this problem occur if you try to enter a shifted function like [f] [->P] (INT), [f] [8] (if Y = 0), or does it only occur on single key functions like [SIN], [LN], [+] for example?

I did this test.
I had no problem to enter a single key functions but for [f]-shifted functions the value remains 51.

---Update---

No. Something more complex.

In some cases really I can successfully enter a single key functions but not [f]-shifted functions.

In some cases - otherwise.

In some cases - cannot both.

[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

[AlexG]

Dear Tony,

it seems, I have a Problem_3 case.

As for the power supply, I use a USB unit from my iphone (2A) and put voltage directly to the contacts dedicated to the battery pack (which is removed). Could it be a source of the problem?

[teenix]

(05-08-2023 05:34 AM)AlexG Wrote:  Dear Tony,

it seems, I have a Problem_3 case.

As for the power supply, I use a USB unit from my iphone (2A) and put voltage directly to the contacts dedicated to the battery pack (which is removed). Could it be a source of the problem?

I guess it should be ok as long as it can maintain 5V running the calculator. I wouldn't have though it would run the printer.

It looks as though the RAM may have failed, but still puzzling that the card read works, assuming that the card program writes to step 29.

cheers

Tony