10 out of 13 27C020 EPROM's I bought at the electronic goldmine are acting weirdly. When I burned them with an all $00 file exactly 6112 bytes on all 10 of them stayed at $FF. Even weirder is that the pattern of unprogrammed bytes is repetitive and the same in all EPROM's. Has anybody heard of this sort of problem? Any suggestions on how to get around this or should I just toss them? Of course they won't take them back.
Are you using a Willem programmer? If so, make sure you select the right programming voltage for the particular chip.
I'm using this one:
http://www.zws.com/products/epromr2/epromr_stage1.html
I checked the Vpp for the 27C020 and it's 12.75+/- 0.25 Volts. I tried programming the chips at 12.5, 12.75 and 13.00 V and the same thing happened each time but only with these 10 AMD Malaysian 27C020's. All my other 27C020's work perfectly. I even considered switching the address lines around to make them into 27C010's but even then they would have about 1Kbyte of errors due to the weird pattern of ?bad bytes.
The Electronic Goldmine wouldn't take them back so it looks like I'm stuck with fool's gold. I was considering raising the Vpp above the rating to see if it would help if I was going to throw them out anyway.
I thought somebody around here recomended these chips so I went ahead and bought 20. I erased them and then tried to program them. I was able to program 4 of the 20! What a bunch of crap! I haven't bought many used eproms before, but isn't that a much higher failure rate than there should be.
I played around with the voltage. I played around with the erase time. I read the datasheet which as far as I can tell they're pretty normal eproms.
Has anyone else bought these? What kind of failure rates are common for used chips?
I saw the same reference to the Electronic Goldmine here and so I bought 13 27C020. I think 3 or 4 out of 13 worked, the rest all had exactly the same bytes that wouldn't program. All the EPROM I bought at a local store worked as have all the ones from Futurlec. Even about 15 pulls from eBay all work perfectly. Where I live there are lots of old PC's left out for scrap. I routinely pry out the EPROM's out with a key and they all work! I have no idea where the ones from the "Electronic Goldmine" (what a misnomer) come from.