hp9815a repair


Sorry to burden all of you with the same problem. But we have found no one able to address the memory problems of our hp9815a. We have all the manuals. We have had it apart to the keyboard, and though some have high resistance, all keys seem to be functioning. There is something going on with memory access/allocation. It has the extended memory option, so should have 2008 steps. But usually only 136 steps are available in program mode. Once we had about 400 steps available. Sometimes we can access the progarm mode, other times not. I am hoping that one of you folks will be willing to put this thing on your bench and to suss this out for us. We have obtained Dr. Duell's schematics from the Australian site. We are unable to make further progress, ourselves. Thank you. Frank email: fbsimson@pharmacy.wisc.edu


excuse me, I omitted a p. my corrected email address is fbsimpson@pharmacy.wisc.edu


Have you tried removing the memory expansion card (the little board on the top of the CPU board) and seeing how the machine behaves then? Is there any change?


Dear Dr. Duell, et al.,
I apologize for my delay in replying. Though I am pretty sure that we tried the 9815A a couple of months ago with the extended memory card removed, I could not recall for sure. It has taken me a few days to find time to try your suggestion. As nearly as I can tell today, removal of the memory card yields the same calculator.
Here are some symptoms.

1)Turn the calculator on in "Run" mode. 0.00 is now on the display. One now hits 2 and 2.00 appears on the screen. Next one hits 6 and 6.00 appears on the screen. One then hits X and 12.00 appears on the screen. Notice that I did not have to hit "enter" to do multiplication. On every key stroke, the printer types "memory overflow". One cannot place a two digit number into the x register. The above sequence should have allowed me to enter 26, for example - no dice.

2)Turn the calculator on in "run" mode. Hit 2 and as before, 2.00 again is displayed. Now go through the stack with the R button. 2.00 only is in the x register, it is not in the stack twice unless you additionally have pressed the enter button.

3) I have no idea why, but the only way I have found to enter PGM mode is to go through the following sequence. Turn power on with switch in "run" position. Then press the following keys in the following order: 1, store, 1, ., recall, 1, ., flip switch to prgm. Now we will see on the display, PC-0000 0136. With the extended memory card removed, there should be more than 400 steps available, not 136. With the extended memory card present there should be about 2000 steps available. Even with the extended memory care present, we still see 136. I believe that removal or placement of the extended memory card has no effect.
Would you like to try your hand at this one? I'll cover postage!!
Thank you!
Frank fbsimpson@pharmacy.wisc.edu

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