Rusty and instable motherboard A500 rev8a

Alex_Retro

New member
Joined
May 20, 2019
Posts
21
Country
Germany
Region
Bavaria
Hi,
in the beginning there was my Amiga 500 wirh a Blizzard Memory Turbo card and a Alfa power Disk and Ram expansion ( without Ram) All the time I thought, that the disk was brocken due to read errors.
After buying am Vampire I figured out that my motherboard was instable, even a more powerfull psu was not helping. System comes up, works for several seconds or minutes and crashes. So I bought a rev 6a. This Board is much more usable. Now I took a deep look into CPU socket of the rev 8a and figured out that same contact parts are really rusty. So I am afraid that this could be one reason for instability. Any ideas if cleaning would be possible or do I need to swap the socket?
Unfortunetly upload of a photo always failed...

Thanks a lot
Alex
 
It's not uncommon for some boards to develop corrosion on the sockets and chips. In many cases a good cleaning to remove the corrosion will help as the corrosion is conductive. Other times the chip sockets will have broken solder joints and these will need to be fixed. A few pictures would help, but from what you say, the board sounds like it could be fixed up without too much hassle.
 
Thanks alot. Any idea how to clean up the holes of cpu socket?
I will give it a try to upload from my notebook at home. Safari / iPhone allways leads to message: unable to uplad failure or wrong format.
 
You're welcome. Rubbing alcohol, an old toothbrush, and a toothpick or needle to gently get into the socket.

Is there any signs of the battery leaking or corrosion around the battery?
 
Fortunately there is no battery on the motherboard itself. Unfortunately the battery on the trap door memory modul is brocken and leaking...
 
Ah. A Rev 8a board without the battery and clock circuit is a bit of a rare thing.

On the trap door memory module, you'll want to remove the leaking battery and clean up that board as soon as you can. Once the board is clean, neutralize the battery leakage with vinegar, then clean again with isoprophyl alcohol/rubbing alcohol.

With my A500, when I got it, it would not work, I found it had a trap door expansion with a leaky battery, but once I removed the battery and cleaned up the expansion, it ran just fine.
 
Well after figuring out that the battery is not ok anymore I removed the module. So that should be no problem.
Beside you will see photo of the socket... after comparing a original MC68K with Vampire and Blizzard I also figured out that there is a big difference in form of pins. Later are more like needles/nails and the CPU itself is more swordlike.
IMG_9966.jpg
 
That's good you've got the old battery out. Leaking batteries will lead to nasty problems.

Yes, the pin form factor has changed over the years. They went to a more needle or nail like style as the old sword like style were subject to bending and breaking much easier. But either pin style should still work with the socket.

Thanks for the picture of the socket. You can see how dull the contacts are, that's oxidation that has built up, which can cause issues.
 
Today I was cleaning the socket with cleaning gasoline. It really looks like the brown stuff is no rust.
Beside of this I measured the resistance between socket and pin of socket. Without pushing and rubbling with the probes I got some mega Ohms.
So I am afraid, that I need a different cleaning. On Monday I will get some contact cleaner for a different try.
 
From the picture it looks like it's just surface dirt. A good contact cleaner should remove that. If you need the socket swapped completely, let me know. I'm in Germany.

Bryce.
 
Thanks a lot. Today I got some cleaner from a friend. It is a little hope to me, if it is only the dirt. Because I do not have the equipment to search for voltage problems or other sources which could lead to instability of this beautiful board...
 
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