Amiga 500 IC issues

[Dandy]

I'd yank that silly IBM ATOnce clone thing but quick. Probably the point of contention in the system too. Yes, yank the 68000 off of that and reinstall directly into the CPU socket. Be careful to observe correct notch orientation.

Why "silly" AtOnce?
What's so silly about it?
Back in the early ninetees I was really glad to have a Vortex AtOnce286 classic in my A500 because it allowed me to run all the MS-Dos soft we used at the CAD school (dbase, word, fortran, c and qb).
(For CAD itself I had DynaCadd plus a tool to convert the 3d CAD data to CNC files for the CNC milling machine and CNC lathe - was slooooowwly, but worked)

Best way to clean IC pins is to simply remove and re-insert them. The friction of the sockets is usually enough to "clean" 'em. If they're truly oxidized, get yourself some very light grit sandpaper or a fiberglass brush to clean 'em up.

Why not an angle grinder? (just kidding)

I always use commercial contact sprays for contact problems, as they're non-destructive in contrary to sandpaper and the like.

I'd be willing to be though most all of your problems will be solved once you get that AtOnce board out.

Really not sure why you thing the AtOnce causes all the problems...

All the chips, but especially the Kickstart, CPU and Agnus chips all deserve to be re-seated.

Fully agreed - but do not forget to treat them with contact spray...

[Dandy]

Hello all,

...
Finally, the CPU has been replaced with a Vortex ATOnce, which is piggybacked over a stock 68k.  Can I replace this back to a regular 68000, or shouldn't I?  I don't really have any use for it.

As you bought the A550 for retro computing/gaming, you might be interested to compare it to a "PC" of that time (I even ran Win3.1 in monochrome mode on it).

Motorola 68000 @ 7.14 mHz vs. Intel 80286 @ 8mHz

In case you don't have the AtOnce manual or boot disk, I could send you a copy of all via e-mail...

[Dandy]

...
I used to work at an Amiga store, and we had nothing but trouble with those.

Wow!
That must really have been a bunch of "experts", if they had nothing but trouble with the Vortex AtOnce286!

I used the Vortex AtOnce286 on a daily basis for roughly 9 years and haven't ever had a single problem with it.

Brilliant piece of hardware and really useful back then, if you ask me.

[Dandy]

...
The ATOnce actually caught me off-guard at first.  There's a badge on the case of the unit that says 386dx/33, but I assumed it was on there by accident.  Then I spent a while wondering how the heck they managed to emulate a 68k on a 286 until I realized that there was a 68k underneath.  

LoL!

What is it actually good for, anyway?  As far as I can tell it's hardware emulation of the IBM PC, but I'm not sure why that would be important.

It was important back in the late 80s/early 90s, if one used the A500 not as a mere gaming console, but as a serious computer. If you wanted some degree of compatibility to schools or business, this was the way to go.
Or you bought the 16 mHz version, that had additional RAM onboard among other things.
Later there even were 386 cards and 486 cards (Vortex "GoldenGate" series) with VGA onboard.

[Dandy]

Taken from Amiga-Hardware.com

"Connects into the CPU slot of the A500, or providing you have the A2000 adaptor card you can also plug this unit into the CPU Fast slot of the A2000.

This card may have problems with A500 motherboards which are older than Rev 6A. The card has printer support, serial support, support for various graphics modes as well as basic MS-DOS sound"

Obviously this refers to the 16 mHz version, as the (smaller) 8mHz version could not be fitted in the A2000 CPU slot. I'm assuming with "A2000 adaptor card" you mean the Zorro busboard from tower conversion kits like from Micronik, as they came with an "A2000 processor board slot".
The 8mHz version could just be fitted into the CPU socket and didn't have any connectors - neither serial, nor parallell. It used the Amiga ports and sound system.