Millipede Troubleshooting information
- 2101 RAM is 4 bits wide, any memory location is made up of two chips, high 4 bits are in memories in row 5, low 4 bits are in memories in row 7
- addresses are not contigous
- Memory 0x1000 - 0x100F are chips N4 and M2
- Memory 0x1010 - 0x101F are chips M4 and L2
- Memory 0x1020 - 0x102F are chips L4 and K2
- Memory 0x1030 - 0x103F are chips K4 and J2
... then back to K7, K5
- Most significant 4 bits are the chips x4, low 4 bites are the chips x2. Example: at memory location 0x1010-0x101F the high 4 bits are on chip M4, the low 4 bits are on chip L2
- Note that each memory address is made up of TWO chips. Also when in test mode, if both chips making up a "bank" read bad, Millipede beep codes may be confusing if both chips that make up a memory location are bad. For example if both M4 and L2 are bad Millipede will beep 4 times, one would think it would beep 3 times since the first "bad" chip would be L2... however it will beep 4 times.
If Millipede beeps 4 times (the first address it reaches) do not assume that chip N4 or M2 is bad... since that's the first address available it may something that affects all memory addresses (such as the multiplexors or buffer chip). Use a fluke if possible to test the range of memory addresses 0x1000-0x13EF to see if it really is chip N4/M2, or one of the data bus control/buffer chips.
- If your sound is missing or low, check the LM324. Besides the POKEY, this is the only IC in the sound circuitry