Greetings!
I've been slowly doing surgery on a 2001-32N but have reached a spot where I'm stuck.
When I first picked it up I had to clean out about 20 years of mouse carcasses and nesting materials. At this point things are pretty clean. Previously I had gotten to a point where it was starting with a fairly stable image and dropping into the monitor with some SRAM issues on the screen. I think (hard to tell) I corrected the ROM problem; one of them was bad. I seem to remember that last I worked on it with the replaced eeprom it actually did get to a ready prompt. I then set out to fix the SRAM.
I distinctly recall that immediately after removing the existing SRAM, adding sockets and reinstalling I had about 30 seconds of blissful success, followed immediately by complete garbage on the screen. Assuming a cold solder joint somewhere, I redid all of the sockets (not fun). No joy.
At this point, at power on I have a screen full of some static character. A second or two later that changes to random garbage that is constantly changing. In point of fact, watching it sit there it does seem to have some sort of pattern to it (perhaps random junk cycling through the SRAM?) but I'm at a loss as to where to go next.
I did read an article or two about the 555 reset circuit sometimes causing the 6502 to do weird things. I don't have a scope, unfortunately, but I did try manually taking pin 40 on the 6502 low for a few seconds. Doing so immediately stops the movement of the random junk and gives me, more or less, a static character all across the screen. Removing the jumper immediately takes me back to junk, however.
Thoughts? Thanks!
I've been slowly doing surgery on a 2001-32N but have reached a spot where I'm stuck.
When I first picked it up I had to clean out about 20 years of mouse carcasses and nesting materials. At this point things are pretty clean. Previously I had gotten to a point where it was starting with a fairly stable image and dropping into the monitor with some SRAM issues on the screen. I think (hard to tell) I corrected the ROM problem; one of them was bad. I seem to remember that last I worked on it with the replaced eeprom it actually did get to a ready prompt. I then set out to fix the SRAM.
I distinctly recall that immediately after removing the existing SRAM, adding sockets and reinstalling I had about 30 seconds of blissful success, followed immediately by complete garbage on the screen. Assuming a cold solder joint somewhere, I redid all of the sockets (not fun). No joy.
At this point, at power on I have a screen full of some static character. A second or two later that changes to random garbage that is constantly changing. In point of fact, watching it sit there it does seem to have some sort of pattern to it (perhaps random junk cycling through the SRAM?) but I'm at a loss as to where to go next.
I did read an article or two about the 555 reset circuit sometimes causing the 6502 to do weird things. I don't have a scope, unfortunately, but I did try manually taking pin 40 on the 6502 low for a few seconds. Doing so immediately stops the movement of the random junk and gives me, more or less, a static character all across the screen. Removing the jumper immediately takes me back to junk, however.
Thoughts? Thanks!
