Official comment

Download the Troubleshooting Guide from here:
http://www.echelon.com/support/documentation/other/troubl2.pdf
It has a section on how to troubleshoot 3150 based devices. It does sound like you need to make a PROM with the EEBLANK program in it and use that to clear out the 3150 chip. Then your original PROM should work again. If your 3150 chip based device runs at 10MHz, then you would use the file "eeb10000.nri" for the EEBLANK process. See this page for more info on EEBLANK: