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HP 25C troubleshooting
04-27-2018, 12:28 PM
Post: #1
HP 25C troubleshooting
Comments very welcome: HP 25C shows *some* signs of life… Occasional zeroes on display. Voltages present, semi-clean (what are typical noise levels? I threw extra tantalum across the 6V – reduced noise, but otherwise, no help). Clocks present. POR seems to POR. Serial data bus shows continuous repetition of the same word (though the signal looks very odd – the lower quarter or so is decidedly not a clean digital signal – is THAT normal?). The SYNC line has a problem – all I see there are +/-900 mV spikes. Makes me think the processor is toast.

Thanks,
Michael
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Messages In This Thread
HP 25C troubleshooting - mdunn - 04-27-2018 12:28 PM
RE: HP 25C troubleshooting - Steve Simpkin - 04-27-2018, 02:21 PM
RE: HP 25C troubleshooting - rprosperi - 04-27-2018, 02:59 PM
RE: HP 25C troubleshooting - mdunn - 04-27-2018, 11:42 PM
RE: HP 25C troubleshooting - rprosperi - 04-28-2018, 12:32 AM
RE: HP 25C troubleshooting - mdunn - 04-29-2018, 02:49 PM
RE: HP 25C troubleshooting - brickviking - 04-30-2018, 12:19 AM



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