Centipede Troubleshooting information
Copyright 2012,2015 Paladin Group, LLC
- 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 0x0400 - 0x040F are chips K7 and K5
- Memory 0x0410 - 0x041F are chips L7 and L5
- Memory 0x0420 - 0x042F are chips M7 and M5
- Memory 0x0430 - 0x043F are chips N7 and N5
... then back to K7, K5
- Most significant 4 bits are the chips x5, low 4 bites are the chips x7. Example: at memory location 0x0410-0x041F the high 4 bits are on chip L5, the low 4 bits are on chip L7
- 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, Centipede beep codes may be confusing if both chips that make up a memory location are bad. For example if both N7 and N5 are bad Centipede will beep 10 times, one would think it would beep 9 times since the first "bad" chip would be N7... however it will beep 10 times.
If centipede beeps 4 times (the first address it reaches) do not assume that chip K5 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 0x0400-0x043F to see if it really is chip K5, or one of the data bus control/buffer chips.
- If your sound is missing or low, check the LM324 at J10. Besides the POKEY, this is the only IC in the sound circuitry
- There are also 2 TDA2002 amps on the ARII board.
H Sync circuitry
When testing H Sync:
- Ensure you have a 12Mhz at pin #2 on P2, if not check crystal or S04 @ N1
- Test each pin in the H Sync table below IN ORDER. If you don't get a correct signal stop, and replace the chip if which pin you are testing before moving on. These signals build upon each other, and will not work if the previous signals do not work correctly.
|signal||Frequency (approximate)||Chip and pin
|6Mhz||6 Mhz||P2 pin #14
|1H||3 Mhz||P2 pin #13
|2H||1.5 Mhz||P2 pin #12
|4H||725 Khz||P2 pin #11
|8H||360 Khz||N2 pin #14
|16H||180 Khz||N2 pin #13
|32H||90 Khz Khz||N2 pin #12
|64H||45 Khz Khz||N2 pin #11
|128H||15.7 Khz||M2 pin #14
|256H||15.7 Khz||M2 pin #13
V Sync circuits
The following are the proper frequencies for the various V sync signal lines
When testing V Sync:
- First test all the H Sync pins in the table above. The V Sync depends on the H sync circuits working correctly.
- Test each pin in the V Sync table below IN ORDER. If you don't get a correct signal stop, and replace the chip if which pin you are testing before moving on. These signals build upon each other, and will not work if the previous signals do not work correctly.
|signal||Frequency||Chip and Pin
|Clock to chip M2||15.7 Khz||N1 pin #10
||1V||7.8 Khz||P3 pin #14
|2V||4 Khz||P3 pin #13
|4V||2 Khz||P3 pin #12
|8V||1 Khz||P3 pin #11
|32V||250 Hz||N3 pin #13
|64V||125 Hhz||N3 pin #12
|128V||60 Hhz||N3 pin #11
|VBLANK||60 Hz Khz||P4 pin #15