A few days ago, I noticed that the LED for address line A4 on the expansion card was not illuminated. I removed the expansion card and connected it up to a 5v power supply and probed the header connectors. All of the LEDs were working fine. I figured there must be either a bad chip somewhere or a solder bridge. After poking around for about 30 mins with a magnifying glass, I finally found the solder bridge under one of the 74S257 DIP sockets. After dragging a hot solder iron through the bridge, and powering up the clone again, I had an illuminated LED for Address line A4. Very hard to see! (I need to get some flux remover I guess .... that would probably make things a bit easier to see).
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