IIe troubleshooting

[Steven Hirsch <snhirsch@gmail.com>]

All,

I could use some suggestions.  I'm trying to troubleshoot one of my IIe 
motherboards, but with little success.  The symptoms are a bit odd.  If I do 
not have an AUX slot video board inserted, it works just fine (albeit in 
40-column mode only).  With any board (I've tried several) in the AUX slot, 
the display becomes total garbage - and it's not limited to an "every other 
character" issue.  My first thought was a problem with one of the custom 
gate-array chips and started substituting from a second, known good board. 
This got me nowhere.

Next step was to sub every socketed chip on the motherboard!  Didn't get me 
anywhere either.  Now, I'm down to suspecting either memory, or one of the 
soldered-in 74-series logic chips.  However, it's hard to see how it could be 
memory, since the machine works fine with nothing in the AUX slot.

Any ideas?

Steve