At 2005-01-25 19:31, Declan Moriarty wrote: >I have a CPU Controller card (8085 based, vintage �1987). The motor blew on >the machine, power surges came and went, and now it won't communicate >with the outside world. One chip is totally (I mean tetotally) >destroyed, right beside the serial port. The com port on the relevant pc >has also been blown, beacuse it was connected at the time. > >What was it? I know it's Texas Instruments, silver topped (SN something) >and 14 pin. It's partner in the RS232 circuit is a 75152 (a Line Driver). On >this mystery chip, pin 7 is 5V ground, Pins 4, 9, 12 are to the 5V circuit. >Pin 4 was really blown off the chip, and there sure was some heat around. >Miraculously, the machine (A huge Turret Punch) > >Has anyone a memory long enough to remember how these circuits were >configured? I am used to MAX 232s with electrolytics around; this board has no >capacitors in sight. No power supply onboard. How did they do RS232 back in >those days?
Normally the boards would get + and - 12 V from a power supply. The standards are quite loose, so anything from say 9V to 15V goes, but 12V was usual. TI had a lot of chips with unusual pin arrangements, sometimes even getting the 0 and 5V the other way round (their RAM's for example). Perhaps the manufacturers put the wrong chip in a board? Often it may work for years and then it blows up. I once found on a Philips development board for the 68070, that the 'chipset-chip' hadn't got his powerlines connected. So it worked purely on borrowing it's power from the data lines. (CMOS can do that...) Another problem, especially with RS-232 may be that the cables connected to it get exposed to electromagnetical fields from for example TL's which wear the circuits down because of the loops in the wires that act as coils. -- Author: Jaap van Ganswijk INET: [EMAIL PROTECTED] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
