The problem of replacing 0.1UF capacitors

Did you try pushing reset? I've noticed on my apple sometimes when it comes up the CPU doesn't come up right (since there doesn't appear to be any proper reset circuitry on the apple 1). And it'll crash the cpu and cause erroneous writes to the screen.If you hold reset while booting the cpu won't even try to start up and it should tell you if the terminal section is working correctly.

In post #1, 'aihk' wrote:

"After I replaced the 0.1UF capacitor today, I appeared a blank screen in Clear Screen, and there was no in the upper left corner@ "

Uncle Bernie advises:

CLR SCREEN working (making screen blank and screen staying blank after release of the CLR SCREEN key) but no cursor appearing means that the cursor state machine or the cursor gates don't work properly. This has nothing to do with the CPU so it has nothing to do with RESET.

The cursor state machine sits in the right lower corner of the "Terminal Section" schematic. Note the CLR SCREEN line and the diode connected to it. The CLR SCREEN line must be released fully (floating) for the cursor state machine to work. Some keyboard adapters drive it all the time, which is wrong. Pulling the keyboard cable would make the cursor appear in this case (if everything else works).

Also check that the 555 timer actually is producing a ~2 Hz signal on its output (this is the cursor blink signal, and if it is stuck, no cursor visible). Follow the output of the 555 timer to the two cursor gates. If they don't work, no cursor either.

This should bring down the number of possible bad ICs to maybe half a dozen.

- Uncle Bernie

UncleBernie wrote:

In post #1, 'aihk' wrote:

 

"After I replaced the 0.1UF capacitor today, I appeared a blank screen in Clear Screen, and there was no in the upper left corner@ "

 

Uncle Bernie advises:

 

CLR SCREEN working (making screen blank and screen staying blank after release of the CLR SCREEN key) but no cursor appearing means that the cursor st

Not to derail the topic. But I've definitely seen times where my apple didn't come up right and it was CPU related as pressing reset would make the screen come good. (No picture or a continuous stream of '\')What I think was happening in those cases is that the CPU crashed as it tried to execute code before the power rails stabilized. Somehow this tied up the interface with the terminal section causing it to misbehave.Thus the reason I suggested holding reset was to take the CPU out of the question.

I'll see if I can get a video of this behavior.

That being said, all of Bernie's advice is good and should be followed.edit: video

https://www.youtube.com/watch?v=cZLIGhZpdVY