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Yes the corrosion could cause shorts, higher impedance "shorts" or open traces.

The battery contents were probably alkaline, you will need to neutralize that with a mild acid, such as vinegar, followed by a thorough wash. If you are going to replace the battery, I'd recommend using one of those off-board battery mounts with wires you solder to the motherboard where the...

One thing that could affect the transfer rate is if the Ethernet interface uses DMA for data transfers or CPU polled I/O. Not having DMA available will lower the throughput drastically.

Possibly bad memory. Have you tried a memory test program?

You will probably have to remove the regulator from the board to test it, otherwise you may see the effects of other capacitors between either the input rail or output rail and ground giving you an impression that there may be a short. The exploded capacitor on the input rail pin is there to...

Looks like it is a tantalum capacitor that is associated with that three terminal 7805 5V regulator next to the failed cap. From the marking on the cap it is a 10 uF 6V part. I'd replace it with a 10V or 15V part if you can find one to give a safety margin.

Wonder if they are the Pinnacle Micro "Gold Card", which was a disk compression processor.  I found this bit of text in a search for "pinnacle micro nubus": Compression boards put the speed on squeeze: Sigma's DoubleUp and Pinnacle Micro's Gold Card being near-instantaneous compression to...

WIth all that fast SRAM on the board and no I/O connectors, I'm guessing the square unmarked chip in the corner is meant to offload some kind of processing function.

Can you see if there is a 3.58 MHz clock signal at pin 23 of the 8530 chip? Maybe there is a bad solder joint there. That clock signal is output by the Mega2 chip, and if it did not make it to the 8530 SCC, the register writes and reads wouldn't function correctly. If the Mega2 chip wasn't...

According to a ROM source listing found at https://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Computers/Apple%20II/Apple%20IIGS/Documentation/, the serial I/O chip test failure code 01 indicates a problem with the SCC register R/W test, which is testing some of the channel A and...

Is it just the diagnostic disk, or a mini diagnostic built into the ROM or a report from GS/OS? Is it possible to just ignore the error report, or does it get in the way of running programs?

Seems to me like you should be able to disable the on-board serial ports and use a card, the ROM slot configuration menus should work for that. Unfortunately I don't have a serial card to try in my ROM 01 IIgs.

Unfortunately it looks like it might be hard to find those chips. Mouser has the 40 pin version listed in stock, but not the 44 pin version you'd need.

Have you checked for leaking capacitors or bad solder joints for the serial chip? Maybe the issue can be resolved with a simple fix. Also, have you downloaded the IIgs Diagnostic disk images? I have three versions, one of the version 3 variants might tell you something more.

I used to run A/UX on my IIsi years ago. It worked fine for what it was. I gave my IIsi away, but still remember it fondly. I wish A/UX would run on my Quadra 631.

Only termination power is available on a standard SCSI interface, including the 25-pin Mac variety.  You should not expect to be able to power the SCSI2SD from that, let alone two of them and the required terminator.

I see the link. It shows settings for the Viewsonic adapter AC-AT Mac II-02, which presumably was meant for a Mac II era system. For 1152x870 resolution SW 1-4 are all on. SW 5-8 depend on the sync method required by the monitor. Sync on Green 5-8 all off.

Is it not sufficient to remove all of the keycaps then the plate?  It is a minor pain, but you should then be able to remove the metal plate and clean up some more.

Wait, made a mistake, 11.32 V divided by 1 Kohm gives 11.32 mA.  If you multiply 11.32 V by 11.32 mA you get 128 mW, which would exceed the rating of the pot by a bit.  You might see if you can find a trim pot with a higher power rating.

If there was 11.32 V across the pot, you divide by the resistance, 1 K, which gives you 11.32 mW, which is well within the specification for your new one.