Apple IIe need help - does not start up

[feltel]

My IIe needs some help. It was put away for quite some time but I wanted to do somthing now. Now it does not start up reliable. One time it starts up normally, the second time the startup beep is played noticeably slower and what looks like output from the machine language monitor is displayed right under the "Apple II" startup banner. The third time it does not start at all. When it does not start at all the 6502s reset pin is at 0V so the CPU does not came out of reset. Also when seemingly started normally it does not take long than the picture is flickering and fading away. Ctrl+Apple+Reset does not work when this happens. I tried without any expansion card but it does not change the problems. I have an A2DVI in the system. When the IIe shows the problems I get an A2DVI debug screen which reads either "no 6502 bus activity" or "waiting for Apple II ROM reset routine".

I checked my IIe enhanced replacement ROMs, they are okay. Also I swapped the 65C02 for an regular 6502. No change.

I don´t know much about the reset circuits on an Apple II, but could be the 558 time and/or the two crystals be the problem?

 

[Callan]

It sounds like it might be the power supply. Have you checked the voltages? Sounds like you're getting good 5v on cold boot, but degrades as you use it. It could be (probably is) your power supply caps are are ready for some new ones.

 

[feltel]

Thanks for your feedback. I should have tested it beforehand. Unfortunately all voltages are present and stable. I also used another Pico ATX based PSU I long since built but never used. The errors are also present using this modern PSU. :-(

 

[Callan]

No worries... I haven't worked on a iie in a while, but this is what I'd check from your symptoms.
First off... 9 times out of 10 it's always been the ram in my repairs, but if not that...
My first basic check would be to look for any tarnished chips since it's been sitting a while.
My next thought would be to check your clock circuit. That would slow a beep / show no activity..

 

[bibilit]

Yes Ram, or bad contact somewhere.

If ram is socketed you can try swapping chips around.

 

[feltel]

Sorry, no soldered RAM but one, I replaced some times ago. I used a dead test ROM (https://github.com/misterblack1/appleII_deadtest) to check for RAM faults. I get one beep which should be data bit zero. This should be RAM at location F10 if I'm correct.

Also the "summary" screen of the RAM test looks like this.


The IIe starts more reliable today then yesterday. Out of a bunch of cold starts I only get a "no 6502 bus activity" or "waiting for reset routine" one or two times. Maybe some caps are "reforming" by being used now.