HP Forum Archive 17

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HP-25C repair Message #1 Posted by MikeG on 4 June 2007, 8:28 p.m. I have one HP-25C that exhibits a lack of programming storage, for example entering any key code in program mode results in <01 1 00> in run mode the unit stores and recalls correctly, also using Sigma+ works correctly. I have kept the unit running without any signs that would be indicative of the clock skewing issue. I haven't tried putting a 20K resistor across data line 11 and ground though. Is this a problem with the ACT or RAM IC?

Re: HP-25C repair Message #2 Posted by Eric Smith on 4 June 2007, 8:34 p.m., in response to message #1 by MikeG I'd guess that you have a unit with two RAM chips (most likely 1820-1630 or 1820-1843), and that the second has gone bad. Check whether Last x works, as it is stored in the same RAM as the user program.

Re: HP-25C repair Message #3 Posted by MikeG on 4 June 2007, 10:18 p.m., in response to message #2 by Eric Smith Thanks, that's it. I do have 1843 RAM. I have another 25C that has other issue but I would like to try the RAM off of it, do you know if the RAM 1820-1610 is pin compatible with 1843?

Re: HP-25C repair Message #4 Posted by Eric Smith on 5 June 2007, 2:14 a.m., in response to message #3 by MikeG I think so, but I'm not 100% certain. Maybe someone else here can verify?

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