Amiga 500 IC issues

[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.

[SuperSpork]

As for the dips, I usually pry a little at each end with a screw driver.  If I work slow, in 5 or 6 passes the chip comes out without a bent pin.

Yeah, but the bottom RF shielding gets in the way of that, and I'd rather not remove that unless I have to.  DIP pullers can help you get IC's out with pretty much zero clearance.

Maybe the problem is with the power supply after all.  How many amps is the 5 volt rail rated for?

I'm pretty sure the power supply is still original, or at least in its original case, so it's 5V, 4.5A.

Do you intend to expand this 500?

Probably not, at least not for the moment.  This one's gonna be a gaming computer I expect, for the most part.  I might invest in an A2000 or other later model Amiga down the road sometime that I may eventually expand.

In any case, I'll start with contact cleaning before I try and moving on to anything more drastic.  Contact cleaner is generally safe on ICs, right?

[Tenacious]

You lost me on the bottom shielding.  I'm talking about gently prying the chips (dual in-line pkgs) up out of their sockets.  This will be required to fully get the cleaner between the pins and mating sockets.  

Some industrial contact cleaners are harmful to plastics and other materials (not to mention ppl).  I've never had a problem with Tuner cleaner from Radio Shack nor with isopropyl alchohol.  You want stuff that evaporates quickly and leaves no residue.  Tuner cleaner is also electrically non-conductive.

Commodore actually made 2 versions of the Amiga P/S brick, yours is the more desirable version.  The other was rated for only 3 amps on the 5 volt supply. BTW, there are hacks on Aminet to convert old XT P/Ss for Amiga use.

[Sandman]

One of the best ways that I have found to clean pins in to just use a regular #2 pencil eraser.  Just enough abrasive to clean the oxidation without damaging the pin.

[SuperSpork]

What I meant was that the RF shielding comes up around the edges of the board (to form more of a cage), and this makes it hard, nearly impossible, to get a screwdriver under one or the other end of most of the IC's.  I can get them out using just one end, but I'd rather not do that.

Although I do recall another trick: Pry one end up slightly and slip a Popsicle stick under the IC so you can pull up with even pressure under the entire chip.

I've used an eraser on some of the pins already, I just want to do a little more thorough cleaning at this point.

[JimS]

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.

Well, it's a small sample size in both cases... you had good luck with your 1 sample, My 2 or 3 customers had bad with theirs. It had nothing to do with their expertise, they experienced the same sort of random problems and general flakiness the the first poster mentioned. It might have been useful back then, now it's just a problem or at best a curiosity..

[SuperSpork]

Just thought I'd give an update to those interested.

I got the CPU to finally sit right, so no more flashing power light for me.  I also had a chance to check my power supply with a multimeter; at least under no load, it's outputting the correct voltage.

The Denise issues I was having were actually caused by the case.  I had noticed that there were a few cracks in the case, some especially large ones in the bottom half of it.  If I take out the motherboard from the case and let it simply sit flat on a table (on top of an anti-static mat, of course), it doesn't have any issues.  Seems that it's cracked enough to the point where the motherboard bends slightly when put into the case, accentuated by the fact that it's missing half of its screws.

So, guess I'll have to repair the case now.  I think I'll try an epoxy repair first, unless there is a better option.

[save2600]

I wouldn't do anything too permanent fastening the case and motherboard together. I'd be more concerned about why a little bit of stress is causing Denise to act wonky. Check for cold solder joints near her socket I guess. The mobo should be able to handle a little bit of warpage without adverse effects. Jeez... you should see what an A2000 mobo looks like while secured to the case! lol

[SuperSpork]

I meant to find the proper screws to secure the mobo in place, it's only being held by 2 right now, and to repair the case separately.

[SuperSpork]

Alright, this is just WAY too ironic.

I took off the screws along the ports on the back so I could remove the RF shielding and get a look at the bottom of the mobo... there was literally a (dead) bug sitting right beneath the Denise chip.  A fly, to be exact.  :roflmao:

So my system had a bug, but I think I've fixed it.