hardie@sask.UUCP (Peter Hardie ) (09/20/86)
The secret 8520 society is alive and well up here in the great white north. I managed to blow away my 8520A chip. I was connecting my amiga up to my ham radio so that it could send/receive morse code and radio teletype (and ultimately add packet radio ability). I had an EXAR 2211 chip set up on a radio shack experimenter breadboard and powered it with 12V from my power supply. The logic output of the chip (it decodes radio teletype frequency shift keying from the radio into a logic signal) was used to drive a couple of transistors which ultimately ground pin 2 of the parallel port if there is a zero and leave it at 5V if there is a one. I disconnected the power and connection to pin 2 while I changed the circuit a bit, then reconnected the 12V supply. Unfortunately, muggins here then connected Pin 2 to the 12V supply instead of to the collector of the output transistor. It may have been my imagination but I thought I heard a tiny hissing sound as the smoke that is kept inside the 8520 chip escaped. But anyway, my amiga would not boot at all. The wee red light came on but it didn't flicker as it usually does and there was none of that tiny tune that it plays as it reboots itself. So off to my amiga dealer, who sent it downtown somewhere to be fixed and one week (and $88 ~= $60US) later, my amiga is back with a working 8520A chip in it. The chip itself was $20 so I got dinged for about an hour of labour which probably wasn't bad considering that they probably have to run a checkout on the beast to ensure that I hadn't melted anything else. So if the amiga fixer in beautiful downtown Saskatoon can replace an 8520 in one week, surely any fixer south of the 49th parallel should have no trouble at all. Now that my little baby is back home you can be sure that I'm going to drive the exar chip with 5V now AND put a fuse on the 5V supply (my 12V supply can go from no load to 12amps with no detectable drop in output voltage). Perhap I'll even add a few protective diodes here and there too. Pete ve5va ihnp4!sask!hardie