BASIC programs known to be good give strange errors (e.g., next withou

[Blacklord]

The problem is most likely a bad DRAM chip if it can be reproduced right at power-on before the system warms up. Replace the Mostek MK4564N type with either 4164, 4864, or 2600P DRAMs. Debug the failed chip by removing the BASIC ROMs and booting into the monitor (TIM). Use the fill pattern 0xaa, 0x55, 0x33, 0xff on several locations in each bank to determine the bad bit(s). Use a logic probe to identify the matching chip (checking CAS in the appropriate bank). Each DRAM was responsible for one bit of the eight involved in each byte. Whereever you find a stuck or dead bit the chip for that bit is the one to replace. You will need the schematics from the service manual for this debug.