Hello, Tuesday, January 20, 2009, 17:26:00, Richard M. Hambly wrote:
R> One of my 53132As, an Agilent unit, s/n KR01202209 fail the power-on self R> test with a FAIL:ROM error message. Cannot say anything about your particular counter, but very often such error is due to 'leaked' EPROM chip, that change value of some memory cells over time. Last years I seen such problems 5 or 6 times with 15+ years old equipment, and in most times original EPROM image still can be read out if you have a EPROM programmer that allow to set arbitrary Vcc for a chip in programming socket. Some background: Erased EPROM cell (actually small piece of metallization between two layers of silicon oxide, acting both as a capacitor and as a gate of MOSFET transistor on underlying layers) reads as logical "one". When it is charged during programming, it start read as "zero". If some cell have small defects in insulating oxide, or just got a hit of some high energy particle, part of charge can be lost and "programmed" bit that should read as "zero" starting to read as "one" under normal conditions (nominal Vcc). There is a chance (very good chance, according to my own experience) that you can find such "partially discharged" bits by lowering (gradually) Vcc and saving read images to disk for further comparsion. Usually I start from 5.0V, make 10-20 reads, saving each one to separate file in a 5V0 directory, then switch to 4.9V, and do the same, saving to 4V9 directory, and so on... Usually it is enough to go below to 4V0... When you analyze saved images later, first compare all files in each directory to each other, you can find some bits that reads unstable at given voltage. Then compare images between nearby voltages and if there is any changes, it may be your "lost" zero bits. If you go too low, some EPROMS that was written before and then erased to program current image may show you some of former programmed bits as zeros - you need to be careful. There was some "erased" EPROM chips that read as blank under 5V but read out their previous content (and CRC perfectly match) when read out at Vcc little below 3.8V (not all brands of EPROM operational at that voltage, though)... If there is a CRC on a EPROM label, it may be very useful in determining that your recovered image is really good. Some devices do CRC check on startup and you can feel yourself safe enough if checksum error is gone. Always keep your original EPROM chip intact and do not expose it to a UV or sunlight (if there is no label that cover their window) until you are completely sure that you have correct image on hand. Use spare EPROM of same type for experiments. BTW: Looks like it is a good idea to have images of EPROMS and calibration EEPROMs (if any) for all equipment in a safe place. -- Best regards, Yuri, UA3ATQ/KI7XJ 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.
