Problems with HP92



#4

I'm repairing a HP92. First, the display only displays segment 'd'. Next, no display at all for the '1' and '7' keys... Printer prints only negative numbers. Many functions, printer prints '-9.999999999'. Any thoughts?


#5

I am guessing you have done all the standard things like checking voltages? Since it is very similar to a 97 inside you could use the 97 service manual for some guidance.

You say it only prints negative numbers, if you key in a number and then press 'PRINT X' does it print the correct digits? IF so that would probably suggest that the ACT and PIK are functional, my gut feel is a defective ROM.

From the picture of the 92's main board it looks like the display setup is the same as in a 97 so the 18 pin chip above and right of the PIK would be a ROM that also is the display decoder with the driver on the display board. You could test the display drivers by separating the boards and powering the display board and apply the appropriate logic levels to the driver inputs to check the display drivers. Given that the d segment is the only one that lights I am surprised that you get anything for 4 as it would not normally light the d segment and that would suggest a problem with the display decoder ROM.


#6

Hi Paul - (the emulator arrived and I've only tested it a little, but is good so far, thanks!) Okay I guess it is the 'g' segment which makes sense now too.


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