Restoring a HP9830B calculator.
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06-11-2014, 06:35 PM
Post: #12
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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! www.datormuseum.se |
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