A590 memory problem after trying to mod

[TjLaZer]

Well I had a spare A590 and some time and thought I would try the power mod hack.  But at the same time I installed 2MB RAM and when I tried to power it up it did not make a sound, but made a bad smell!  Turned it off right away and the RAM chips were hot and smelly.  I'm sure they got toasted.  The mod looked fine not sure what happened.  Removed the mod and tried to see if the thing was still alive.  Well ROMs were toast so I installed a new set and it fired up.  But now I cannot get any RAM to show up. Tried some 512k RAM from my A2091.   Any ideas?

[TjLaZer]

You've probably melted the PCB somewhere. Go over it with a magnifying glass both sides looking for a burnt track.

Perhaps you put a RAM chip in backwards and inadvertently connected +5v and GND?

Thanks.  I will have a look over on my board.  

I wonder if I got the wrong RAM for my A590.  Is this the correct RAM for it?

http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_42315_-1

[TjLaZer]

That is the correct RAM, 256K(bit)x4 (128Kbytes each) @ 80ns (120ns minimum required) so 16 chips should have given you 2Mbytes. I think all 256Kx4 PDIP DRAM chips have the same pinout.

Should have been fine. Did you check each one to make sure they didn't send you a rogue one?

Well I managed to get 512K working without errors, but anything beyond that I get errors and lockups!  I also noticed that some of the memory sockets melted a little bit from the heat!  Really did a number on it.  But at least it works with 512K...  I swapped over all chips from a working A2091 to see if it was one of the socketted chips.  No juice.  Not sure what else to try.