HP97 memory fault?

[teenix]

(09-16-2017 05:25 PM)Hans-Peter Wrote:  A optical check of the CPU Board with the roms shows a slide black film over the silver legs of the roms, like my silver can in my livingroom. No corrosion like a battery drain.

Is there any chance to fix it without change the complete Mainboard?

Hans-Peter

The "black" is probably age related corrosion or discoloration on the surface of the IC pins and may have affected the soldering.

If you have a magnifying glass, you should see shiny silver looking solder joints on all IC pins. If there are some that look a dull grey colour and perhaps pitted where I joins the actual pin, it might indicate a dry joint causing the problem.

With care, these can be resoldered.

It is possible that a memory "bit" after all this time is beginning to fail either in the ROM or in RAM. It may work ok for awhile, then fail on a specific read or write causing the crash. If it was a totally failed "bit" then the problem would most likely show up all the time and programs would not run.

If the calculator functions ok with all normal operations for a long period of time, including storing and recalling to/from memory, then I would suspect a ROM issue where the PRGM/RUN microcode resides, or in the program memory.

These types of problems are hard to solve without parts substitution or specialist test gear.

If it is a program memory problem, you might be able to sequentially test it by building up a simple program. That might cause a fail after a certain amount of instructions are added.

LBL A
GTO A
------------
LBL A
+
GTO A
------------
LBL A
+
+
GTO A
-----------
etc

Can you reliably on multiple times enter a program and verify by SST in PRGM mode, wait 5 mins and verify again.

cheers

Tony