Hello all,
I have a 128K logic board. It's been upgraded to 512K with the modification and new sockets for replacement ram chips installed. I did at one point see this board working but it failed rather suddenly. Not the smoke this time but it makes some rather loud beeping noises on repeat which seem to line up with the video glitching.
It's strange. The rom does seem to be active and CPU does seem to be trying to execute something. The screen state changes in a somewhat similar pattern on start. Pressing reset will repeat that process. It looks as if some of the RAM addressing circuitry has gone bad but I've probed rather a lot to no end so far.
Thought I'd see if anyone has found anything similar. I do have a donor board fortunately but some of the parts are already missing. Here's a video of what it's doing.
View attachment IMG_9538.MOV
I've tried swapping ram around to see if anything changes. Sometimes that raster turns to more of a checkerboard.
Any thoughts on this are appreciated. I might have missed something while probing but if anyones seen anything similar, it might help me to figure out where to poke. I have a ram tester coming today although voltages and data look ok on what I've seen so far. I'd also expect something a bit different if ram isn't ok. Larry's books seem to show other fault indicators for that failure mode.
I have a 128K logic board. It's been upgraded to 512K with the modification and new sockets for replacement ram chips installed. I did at one point see this board working but it failed rather suddenly. Not the smoke this time but it makes some rather loud beeping noises on repeat which seem to line up with the video glitching.
It's strange. The rom does seem to be active and CPU does seem to be trying to execute something. The screen state changes in a somewhat similar pattern on start. Pressing reset will repeat that process. It looks as if some of the RAM addressing circuitry has gone bad but I've probed rather a lot to no end so far.
Thought I'd see if anyone has found anything similar. I do have a donor board fortunately but some of the parts are already missing. Here's a video of what it's doing.
View attachment IMG_9538.MOV
I've tried swapping ram around to see if anything changes. Sometimes that raster turns to more of a checkerboard.
Any thoughts on this are appreciated. I might have missed something while probing but if anyones seen anything similar, it might help me to figure out where to poke. I have a ram tester coming today although voltages and data look ok on what I've seen so far. I'd also expect something a bit different if ram isn't ok. Larry's books seem to show other fault indicators for that failure mode.
