Hello, Friday, December 19, 2014, 21:34:35, Poul-Henning Kamp wrote:
PH> -------- PH> In message <[email protected]>, Bob Camp writes: >>A *lot* of errors on the 5370’s (A or B) can be traced to a couple PH> of fairly simple issues: PH> 4) (E)PROMS loosing their memory. Sometimes it is possible to "extract" original contents from "leaked" EPROMs (and some parallel 28-series EEPROMS) by reading at reduced Vcc. I done this several times with old test gear (Marconi 2955 sitting on my workbench had "leaked" calibration data in EEPROM, for exapmle, and it was recovered successfully). Erased cell reads as logical "one", programmed as log. "0". So, with time, some programmed bits in "weak" cells revert to "1". Usually I read chip at 5V a number of times, and save data in separate files, then gradually decrease Vcc in 0.1V steps and continue to save everything. Usually at some point there is no more new "zeros" appearing, and comparing EPROM against readed data multiple times does not produce any difference. If so, it is relatively good chance that we have in buffer the same data that was originally programmed. Data is programmed to a new chip, and old one saved for reference to return to it if something going wrong. If it is impossible to find "stable reading" voltage (for example for older NMOS EPROMs that give up at 4.5V or so), it is still possible to statistically find "unstable" bytes, processing a batch of files readed at different voltages and from heated and cooled chip, but result is much less reliable. I understand, that it is always better to have a backup or to find correct image from another unit, but sometimes EPROMs contain factory calibration data, and you have to extract all that possible from original chips. -- Best regards, Yuri mailto:[email protected] _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
