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Conference 7.286::atarist

Title:	Atari ST, TT, & Falcon
Notice:	Please read note 1.0 and its replies before posting!
Moderator:	FUNYET::ANDERSON

Created:	Mon Apr 04 1988
Last Modified:	Tue May 06 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	1433
Total number of notes:	10312

143.0. "Dead Serial Port" by CIMBAD::POWERS (I Dream Of Wires - G. Numan) Tue Jun 28 1988 13:37

    
         Last week, in the electical storm, we had go through New England,
    my atari happened to be on at the time.  I quickly shut it down,
    but before I could get it shut down, It appeared to have gotten
    hit by a surge or something.  I was running MSH from mark williams
    at the time, and I got a whole stream of characters show up on the
    command line, that I didn't type.  After the storm had passed, I
    repowered up my atari to make sure it was alright.  Everything seemed
    to be working, except my serial port.  There are two 6850 ACIA's
    in the atari's, one for the midi, and one for the serial port.
    My question is, is this the only chip which might make the serial
    port stop working?  Should I take it into be serviced, or just replace
    the chip myself?  It would probably save me a lot of money, if I
    changed it myself, seeing that chip only costs a couple dollars,
    would it require a lot of work, to replace it?  I imagine Atari
    probably has it soldered in.
    
    Any thoughts/suggestions
    
    Thanks
    
    Bill Powers

T.R	Title	User	Personal Name	Date	Lines
143.1	my quess is that it's not the ACIA	BOLT::WARE	Ralph Ware @ MSD/AD	`Tue Jun 28 1988 13:54`	6
	I don't have schematics, but there must be some sort of RS232 driver and receiver between the 6850 and the connector. These would be the most likely point of failure. rw
143.2	68901 is AUX port.	PRNSYS::LOMICKAJ	Jeff Lomicka	`Tue Jun 28 1988 14:30`	15
	I expect that .1 is correct about the line drivers and receivers. Note, however, that the two MC6850's are the keyboard and MIDI interfaces. The serial port is the much harder to find MC68901 multi-function controller. I think the 68901 is socketed in some systems. There is some additional testing that I would perform before taking a soldering iron to the Atari. Hook the modem port to a terminal with a null modem cable, and run a terminal emulator. Can characters go either direction? If it works one way but not the other, it's going to be a line driver/receiver. If it doesn't work at all, it's more likely the MC68901. (Although it could be BOTH driver and receiver.) I know that you are also in Hudson. If you would like, we could get together and solve this problem. I'm not shy about poking around inside the Atari with a soldering iron and a scope probe.
143.3	68901	CIMBAD::POWERS	I Dream Of Wires - G. Numan	`Tue Jun 28 1988 15:22`	16
	Jeff, My computer still works, so I doubt that the 68901 is dead. I don't think that it would work, if it was dead. Is it possible for a chip like that to be partially working?? In fact I have since the storm, been playing around with timer A on the 68901. I am sure it is not my modem that is at fault, since I have two, an Avatex 1200 baud, and a Digital 2400 baud, and neither seems to work with the serial port. Thanks for your offer to help me out, Ill send you some e-mail. Thanks again Bill Powers
143.4	1488 and 1489	BRSDVP::PIGEON	NOT the FAX730 specialist	`Thu Jun 30 1988 13:09`	15
	from the drawings.... re .0 The second ACIA is used for the keyboard. re .2 .3 The 68901 is driving the RS232 port, but all signals transit thru gates in chips U14 and U13. (1488 and 1489). So if you want to use your iron, you better look at those first. (they may be labeled otherwise on your board, my drawings are for the module C070522 rev A ) Good luck.
143.5	Receiver was bad, it's now replaced.	PRNSYS::LOMICKAJ	Jeff Lomicka	`Thu Jun 30 1988 15:21`	4
	Thanks for the hint. Bill and I fixed it Tuseday evening. It was the 1489 receiver, and I had speculatively bought one on the way home, since it was the prime suspect. (They were on sale half price this week at the local Radio Shack store.)
143.6	The Driver did it	DOOBER::MESSENGER	An Index of Metals	`Thu Jun 30 1988 19:40`	4
	Recalling from my terminal-repair days (not for DEC) these problems are almost always due to MC1488/89 failure (good thing too; they're cheap) - HBM