Troubleshooting a 286.. oscope level!

ethan at ethan at
Sat Oct 3 00:21:39 CDT 2015

Hello everyone,

   I'm working to troubleshoot a 286 laptop style computer. I've kind of 
hit the end of my knowledge and wondering if anyone has any insight.

   The computer in question I've never seen run. So I don't know normal 
behavior. There were a few caps inside that were leaking electrolyte, I 
cleaned it all up and replaced them. A few traces look a little bit 
corroded but test fine.

   First thing I'm thinking, is did the BIOS eproms loose a bit or two of 
data from age? Bit rot? I did read off the two BIOS chips (high and low 
pair I assume.) I can see text like Copyright Pheonix Technologies 1988, 
but I can see that for instance the first character of the text Copyright 
is wrong, it's a P in one file and 9A in the other.

   Second thing I hooked up Oscope and cut on computer. It never does a 
floppy seek. When I poke around the 27c256 EPROM I see constant activity 
on all address lines, and all datalines. This includes the OE pin as well. 
Would a normal runnng computer hit the BIOS that much?

   Any thoughts appreciated!

Ethan O'Toole

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