DRAM memory for NorthStar Horizon

There is little value in replacing all the chips. Replace the bad ones. The chips you purchase will be NOS. They are almost as likely to have one or more bad ones as the ones on your board. As was mentioned, it looks like the chips you have are the those that were half good. Also look for chips with the same pinouts from other manufacture. Most of these 8K and 16K chips were interchangeable, although Motorola was famous for making something not match other manufactures parts. Things like a select inverted or RAS vs CAS refresh. Many RAM test do not test retention of DRAMs. Most are designed to hold for a minimum of 2 seconds but many can hold for much longer. You can not tell if your board is doing refresh if you are constantly reading the chip. It is necessary to stop reading for a period of time ( with refresh still active ) and then go back and read the memory locations. Funny failures can sometimes be traced to lack of there being a refresh cycle. Just reading a location refreshes it so it can hide the fact that it is not getting a refresh cycle in many RAM test. Dwight