HP-97 Flashing Display


I've done some searching on the Internet, but can't find a definitive answer to this, so could someone please reassure me:

When running a program on the HP-97, is it usual for the LED display to show all sorts of weird characters until the program completes?

If I run the diagnostic program from the Standard Pac, after the intial 2 second run, it displays complete rubbish for about 90 seconds at which point I get the correct values printed out. I assume this means that all is well...


The experts will correct me if I am wrong but I think that it is a design function; i.e. done on purpose.

The logic goes like this, if you run, say the diagnostic test as you did and instead of flashing, the screen was blank for the complete 90 seconds, how would you know the calculator was actually doing something?

It goes back to the early computers with multi light displays (1950 - 60's). If the computer stopped running at a certain point then the light display could be used to interpret where the program stopped.

I think that is also why the HP 41 series have the flying goose instead of a blank display also. I replace my goose with the 'aview'; WORKING or THINKING just for effect.

I use the flashing screen display on my 67 in the cockpit as a bit of computer humour, 'the calculator is thinking'.

Cheers, and Merry Christmas

Edited: 21 Dec 2007, 1:05 p.m.


Put the following program in to test all program memory registers and then copy to a card. Use a good HP 97 for this to get it on the card and then use the card on any other HP 97 and 67's you are fixing.

In program mode press the + key 223 times to fill all program registers with the + command with line 224 a R/S command:

001  +
002 +
003 +

223 +
224 R/S

in run mode enter 1 four times.

Now hit runstop and you will see in the flashing rubbish that the display is actually adding the number 1 incremently to 224; i.e. you will see the nubers adding in the flashing rubbish. The answer will be 224 if all progam registers are accessable.

You may ask why you need such a program but the following occurred to me with and HP 67. The shorter programs were working but some of my longer programs were haulting at an unknown point. On a good calculator I loaded the above program onto a card and inserted in to the HP 67 with the problem. The program continued to hault at line 113 indicating a fault in the memory chip containing that register. Had to swap out the chip for a new memory chip.

I now run the above "memory test" program first to see if the registers are functioning on my HP 67 and 97 restorations, followed by the HP test that you ran.

Cheers, Geoff


The 97 service manual documents a "Program memory test program card" that provides detailed fault isolation.

001 ISZI
002 ISZI
003 ISZI
004 ISZI
005 ISZI
006 ISZI
007 ISZI
008 ISZI
223 RCLI
224 R/S

See the service manual on the Museum CD's for the use flowchart, it is on page 4-8.


programs and etc on the HP 67. That one is good as it also tests the incremental step function. But will it halt at the bad memory register? Probably.


Cheers, Geoff

PS anyone that hasn't got the disks should buy them, mine are version one fromabout 6 years ago but still function wonderfully.

Just fired up my HP9114B disk drive and about to load up my hp41cx with all the programs on the disk for work. Been using the HP67 so much I put the 41cx's in storage for the last 4 years.


But will it halt at the bad memory register? Probably.

No, it doesn't. Using the flowchart and the resulting displayed values, it will determine which part needs to be replaced.

It always starts with replacing the CRC IC, 1820-1751 which contains all 224 program registers.

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