Mac Plus success - clean contacts!

Mark Tapley mtapley at swri.edu
Mon Aug 13 11:36:32 CDT 2007


All,
	another update on my Mac Plus - previously, I've had trouble 
with getting the +5V supply adjusted right, and noticed that 
reseating the power cable connectors helped.
	This time, I actually took some measurements. Looking from 
the solder pad on the far side of the power board, through the 
connector, the cable, and the connectors on the digital board, to the 
solder pad on the far side of that board, I saw anywhere from 1 to *5 
Ohms* through that cable. No wonder it was not reliable! I'm 
astonished it ever ran long enough to get through the RAM checks!

	Pulled off both connectors, ran a VOM probe back and forth 
through each slot on both ends of the cable a few times. Got some 
400-grit sandpaper and lightly sanded the pins on the board 
connectors, swabbed them off with Q-tips and isopropyl alcohol, then 
swabbed on a trace amount of silicone oil (in hopes that it'll be a 
while before I have to do this again). Resistance measurements, after 
reassembly, went down near enough 0 that I would not attempt to put a 
number on them other than << 0.2 Ohms.
	Pulled out all of the SIMMS, scrubbed their contacts with 
Q-tips and isopropyl, and re-installed. Reseated the CPU (Brainpower 
Accelerator daughterboard).
	Tuned the +5V supply back *down* a little, to about midway 
between where it would crowbar and where it wouldn't start (This 
looked on my ancient VOM to be around 4.95 V).

	System has been running solidly for several days now, through 
multiple power cycles and multiple extended play sessions. My 
6-year-old is getting reacquainted with Dark Castle and Sim City.

	Hope this is useful; questions welcome!
-- 
						- Mark, 210-379-4635
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