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AST XFormer/286 BIOS Checksum error

The AM27128A-4DC requires 12.5v VPP not 21v, The Intel D27128 does require 21v VPP, It's possible that:
1. Both Eproms are bad.
2. Your new power adapter is not working as it should. ( for the Eproms that require 21v VPP )
Yes, I think the two sets of EPROMs are defective as the Vpp lamp illuminated during the write phase but showed the original error displayed in an earlier post.
 
After several tries this week to gt the AST motherboard to trigger the Landmark Supersoft diagnostic software, the result was a no go as the software failed to trigger a sound and/or MDA response. I rechecked the EPROM's to verify if the software had loaded and it was there as visualized by checking the buffer after reading the EPROM. The odd and even chips were loaded into their correct positions. I think the Landmark was more in tune with working with an AT machine rather than this modofied XT design with the 286 processor.

With the possibility of failure, I have acquired another 286 motherboard that is more like that of being an AT rather than XT. The board is unbranded, however, I was able to find a match for the board on the Stason.org website for the jumpers. Sellers pictures showed Award BIOS circa 1989.

I wanted to thank all those fellow members who assisted trying to solve this problem. Their help was greatly appreciated.
 
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