> From: Phil Beesley <[EMAIL PROTECTED]> > Date: Tue, 30 Mar 2004 23:02:39 +0100
> Thanks for another informative post, Jeff. As far as programming > *EPROMs goes, how easy depends where you live in the world. Last year > or so, a work colleague mis-flashed an EEPROM in a PII motherboard. We > checked the typical UK catalogues (Farnell, RS etc) but the only vendor > who had a suitable package in stock was in Sweden and ordering would > have cost more than a replacement motherboard. In the end, we peeled > the labels off 100 or so surplus ethernet boot ROMs until we found a > match... It should (usually) be easier for compact Mac and Apple II > ROMs because the socketed ROMs are standard but many people have > reported problems buying blanks at a reasonable price. Thank you for the kind words. That's an interesting anecdote. I assume in the case you mention above that the chip in question was one-time-programable, OTP? An EEPROM which was mis-flashed should have been erasable unless the chip was destroyed, e.g. by applying the wrong voltage to the wrong pin or something. I am a bit confused as to why you had to replace the chip. Did your colleague install the chip backwards? The older blanks are getting hard to find and pricey as you say. Especially the lower capacity < 1 Mb chips. 64Kbit chips can be a downright pain to find. I bought a dozen 64Kb EEPROMs in a PLCC package several years ago for my Outbounds and I think I paid $3 - $4 each for them. Now I can't find them at all. For 1 Mb and above you can usually substitute a modern flash chip for the old ROM or EEPROM chip, provided that the chip just needs to sit in the machine and be read. If the machine needs to be able to update the chip, then this usually won't work. Also, when substituting a Flash for a ROM, one often needs to tie the WE_ (write enable, active low) pin to the 5V pin in order for the chip to be readable. And some flash chips have a Reset_ pin which must be tied high as well. If one is desperate and handy, it is possible to adapt larger capacity chips to the older applications, but it's messy and requires some available space, because one must adapt the pinout of the newer chips to the older chip pinout. > (For help on fixing old Macs, don't just look to the Mac community. If > you are working on a basic circuit /psu or you have schematics, an > old-style radio shop is a good place to visit.) Some other places to get help are the news groups such as sci.electronics.repair, sci.electronics.basic, sci.electronics.components and there's another helpful group but I'm not going to be able to remember the exact name and I'm not at my home computer where I could pull it up. It's something like comp.sys.ibm.pc.hardware.chips. That's a pretty interesting group. If you're not in a big hurry, the Electronic Components section of Ebay under Business and Industrial is a pretty good place to pick up non-volatile memory at a low price. A general method of shopping for a replacement non-volatile memory chip is to take the chip you have/need, identify the manufacturer and see if you can get the datasheet for that chip. Then go to other manufacturers (Atmel, Winbond, SST, ST Micro, Samsung, Hyundai, Etc.) and look for chips of the same capacity and organization and get their datasheets. If the pinouts match you may be able to do a substitution. If the chip is going to be treated as a ROM, this will almost always work. It the chip needs to be updatable in place, this can be considerably more complex. One can also use chips one capacity step up sometimes, e.g. 1 Mb when you need 512Kb. Jeff Walther -- Compact Macs is sponsored by <http://lowendmac.com/>. Support Low End Mac <http://lowendmac.com/lists/support.html> Compact Macs list info: <http://lowendmac.com/lists/compact.shtml> --> AOL users, remove "mailto:"; Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive:<http://www.mail-archive.com/compact.macs%40mail.maclaunch.com/> --------------------------------------------------------------- >The Think Different Store http://www.ThinkDifferentStore.com ---------------------------------------------------------------
