Where can I find an OS ROM chip replacement?
The ESQ1 and SQ80 use two 27C256 EPROM chips (OS HI and OS LOW), while the ESQm rack-mount module uses just one single 27C256 EPROM chip in the OS HI position. You can purchase them from http://www.mouser.com for about US$3 each plus shipping. Be sure to get at least two of them (unless you only have the rack mount ESQm). One current Mouser stock number (as of mid-2007) is 511-M27C256B-15F. If this particular model becomes unavailable, these chips are made by a number of manufacturers. Search Mouser (or your favorite parts supply house) for “27C256 EPROM” and make your selection based on price and availability. Look for specifications similar to “UV EPROM 256K (32KX8) 150ns” although the speed is not critical. (Speed of the EPROM is given in the last number, next to “ns”, or nanoseconds) 27C256 EPROM’s are manufactured in a number of form factors. The ESQ uses the rectangular 28 pin UV-Erasable version. “UV-Erasable” means the chip can be wiped clean with an ultraviolet light source an
