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Restoring a HP9830B calculator.
06-11-2014, 06:35 PM
Post: #12
RE: Restoring a HP9830B calculator.
New problems

Well. The o-rings arrived in the mail and they were easily replaced. The clear leader lamp was broken so I replaced it with a white LED (yes I know it should have been a small 5V 60 mA filament lamp, but I argue that if a LED had been available in 1972 they would have used it). Then rewind started to work. The solenoids were just stuck.

I also tried the MARK command but it kept running for quite sometime until it stopped and then the machine was completely unresponsive. Weird.

When rebooting I recognized that it was failing to calculate things. For example 2+2 became 8.4444444, but 3+1 became 6.4444444. Strange. This used to work perfectly.

Just pressing a number and then execute also gave weird results.
0 reported back as 2
1 as 3
7 as 9

but 8 as 32.9444444
and 9 as 33.9444444

18 as 20
19 as 21

but

20 as 42

11 as 33
30 as 52
1000 as 3222
SQR(2) resulted in 2.22636363
and 2^2 in 41.96520965

What is going on?

However I could type in a small BASIC program like 10 DISP "HELLO WORLD" 20 GOTO 10 and it would run correctly.

It seems that it adds 2 to each digit but when the digit produced carry (8+2) then it gives a weird float.

But it cannot simply be some kind of problem in the keyboard input since it is handling line numbers OK. AUTO# also works just fine so basic integer arithmetic works OK.

Maybe it has to do with float numbers? I think that the memory subsystem is working since it can store a BASIC program and run it.

Since it actually is capable of doing a lot of things most of the microcode has to run properly.

Could there be some part of the ALU that is not working fully. As far as I understand the float format is implemented using BCD and one of the ALU PROMs together with portions of the A register and T register are involved. I think it is unlikely that the it is the T register that has failed since then I would probably have bigger trouble. But maybe the portion of the A register that handles BCD? Maybe some output stage has failed? Or the BCD ALU PROM?

It seems that I need to create some extender boards and start up my trusty old HP1664A logic analyzer.

All help highly appreciated!

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RE: Restoring a HP9830B calculator. - MattisLind - 06-11-2014 06:35 PM



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