Another visit to the Macintosh collector and I came home with a SE/30 and an extra SE/30 logic board. Both of the featured Simasimac symptoms. That is a problem related to the leaking capacitors and it usually causes visual artefacts on the screen.
I was told both logic boards were already recapped but closer inspection revealed the job being done badly. The logic boards were not identical as the older one had CPU on a socket instead of being soldered straight on the board.
First I washed both boards with IPA but that didn't do any difference. Then I took out my multimeter and using some schematics found online I went through each capacitor. It turned out that on the older board C9 capacitor's soldering pad was destroyed during earlier capacitor replacement. With help from 68k forum I soldered a tiny jump wire and that actually fixed this logic board.
The newer board had all the capacitor connections fine but after further measurements based on the schematics revealed a bit more complicated problem. The A0 line was damaged between UD8 (pin4) and UK6 (pin 10), most likely due to leaking electrolyte. But a bit longer jump wire solved this problem, too.
Now I had to working logic boards but unfortunately the only boot disk I had for the Macintosh died. I cleaned and lubricated the original disk drive but the original floppy refused to boot anymore. I could not source a new boot floppy disk locally due to COVID-19 so I went a bit extreme and bought a second hand SD2SCSI card. At the same time I managed to find a reasonably priced Asanté SCSI to Ethernet adapter.
Software setup was a little bit complicated but I managed to get SE/30 to startup using System 7.5.5 and the correct extensions for the adapter. On one of my RaspberryPIs I have AppleShare server (netatalk) so it is now rather easy to move files between modern computers and vintage Macintoshes. Web browsing is also possible, but most sites require support for https instead of plain http and old Netscape 2.0.2 doesn't work very well with current TLS protocols. But using a proxy rendering one can access pretty much any page.
Meanwhile, I somehow ended buying two more old Macintosh computers. 512Ke and Plus. Both obviously broken, so some more vintage computer repair stories coming up...
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