I understand that you should not be able to get a reading with a logic probe on the crystal. I am really at a loss at this point & decided to check it anyway, it is reading low. History of the board is that it was working fine and then it started to do random weird sounds and graphics and the game would freeze. Restarting the game would clear it for a couple of minutes and it just got worse over time. I have been comparing logic probe readings against a working pcb.
The bad pcb will boot up as stated above and a lot of the chips probes similar but not all the same and then the game will freeze up and most pins will be stuck, some still do pulse. When the pcb freezes all the pulses change and I get a voltage drop for a second from 4.85 to about 4.6. I took a chance and replaced the crystal and it did not help. A few of the chips in the clock circuit have been replaced in the past by someone else before it quit working. I do not fully understand how to read all schematics or how to fully understand how all chips work, hence why I compare pcb's. Can someone please help me figure out why the crystal is low. I have determined that the funny sounds are because the adress in is wrong resulting in a bad out. Same issue in a good majority of chips I probe in the ram/ rom area of the pcb. Game had worked fine at this voltage as well and so does the working pcb. All ROMS have been verified good. I have logic probe and can get a hold of a o-scope but neither one of us really know how to use it.
The bad pcb will boot up as stated above and a lot of the chips probes similar but not all the same and then the game will freeze up and most pins will be stuck, some still do pulse. When the pcb freezes all the pulses change and I get a voltage drop for a second from 4.85 to about 4.6. I took a chance and replaced the crystal and it did not help. A few of the chips in the clock circuit have been replaced in the past by someone else before it quit working. I do not fully understand how to read all schematics or how to fully understand how all chips work, hence why I compare pcb's. Can someone please help me figure out why the crystal is low. I have determined that the funny sounds are because the adress in is wrong resulting in a bad out. Same issue in a good majority of chips I probe in the ram/ rom area of the pcb. Game had worked fine at this voltage as well and so does the working pcb. All ROMS have been verified good. I have logic probe and can get a hold of a o-scope but neither one of us really know how to use it.