Apple /// startup problems - please help

[MarNo84]

Hi there,

my beloved Apple /// won't startup anymore... if I power it on, there is just the red lamp on the motherboard and the white/yellow one under the keyboard which work as usual. No check or anything from the floppy drive and the screen stays blank.

The only way to get something on the screen is by keystroke reset == Control+Reset, Control+Apple+Reset - after that the computer tries to access the floppy drive and after that with fingers crossed, I will get an "Retry" on the screen - sometimes it will put some extra blinking letters to that "Retry" - as seen on the attached pictures.

I uploaded a short demonstration video to my YT channel:  https://youtu.be/to9KG2FWJbw

What could cause such illness to my beloved little Apple? Voltages from the power supply seems to be in normal state (I checked it with voltmeter).

If I try to boot from any SOS Disk, it will freeze - same goes for serial ADTpro - stops at kernel loading.

Any ideas what component on the board could cause such trouble? I already reseated every IC on the board, double checked the RAM-Board (5V, 256K) - same results with removed RAM-board?...

Please help me getting my baby up and running again  [ ]

Marcus

 

[david__schmidt]

It's like it wants to work... have you tried giving each of the chips a little push to re-seat?

 

[MarNo84]

It's like it wants to work... have you tried giving each of the chips a little push to re-seat?

Yes, I already re-seated every single IC. Cleaned the pins and after all I gave every chip a little extra push on the board while turned on - no sign of change.

:-/ It just happens from one day to another...

 

[david__schmidt]

Understood.  The reseat trick is usually good for the intermittent gremlins like this.  Does it have anything to do with heat (i.e. once it's warmed up, it doesn't happy any more) or anything like that?

 

[MarNo84]

Hmm..nope it's the same behavior on cold or warmed up start - I tried to let it 'run' for a couple of minutes - 30mins was the longest time I waited. No changes at all - besides a very hot memory board resistor( I think that white, big 'resistor' on the memory board get's usually darn hot?) I mean, it hurts after a few seconds, once it's heated up - this takes about ...hmm..5 or 6 minutes?

The strange thing is...I can do a manual reset and then it 'seems' to startup normally - until I try to load any SOS or Apple Emu Disk.  Well, the confidence Disk starts up like a charme and passes all tests :-/

 

[david__schmidt]

So a physical reset starts it up.  That suggests that the 6502 isn't getting a reset signal on initial bootup... which could be a logic failure on the main board (that neither the POST nor the diagnostics picks up).

 

[MarNo84]

Hmm, that's a good point - something I didn't think about... So - what could be in that logic 'circuit' that could be my problem? Are there any steps-by-step check ups to consider?

 

[david__schmidt]

This is a level of diagnosis beyond me.  Someone smarter with an oscilloscope would be able to probe the 6502 /reset line and see if it is pulled low on startup vs. when you hit the reset button.  Then they would backtrack from there to see why it's not firing at initial startup.

 

[MarNo84]

Hmm... I'm actually that far to just swap the few capacitors on the board first and hope to fix the issue ... I don't have anyone near me who could check it or help with oscilloscope :-/

 

[david__schmidt]

It's more likely logic than capacitance, unfortunately.  And blindly replacing what might actually be good parts carries its own risks.

 

[MarNo84]

true...damn -but I need to do something with it xD I don't know how to locate the faulty area or parts, so I just want to start doing the oneday neccessary swap of these caps

 

[MarNo84]

OK strange - I did try out the dealer diagnostics disk again. Everything went through flawlessly (ok, I'm too stupid to use the keyboard test correctly) except the 5V memory test?? It starts loading from the disk and then nothing happens...

I also did another memory direct test that went trough about 280 rounds of memory test without any errors? What could affect the logic and/or memory? I guess I won't do the cap swapping until the real issue is solved. So I need someone who can help me - preferably from germany or neighbour countries around germany - just because of shipping the board I will pay for the repair :-/

 

[bibilit]

Did you tried another floppy drive ?

 

[MarNo84]

Did you tried another floppy drive ?

Hmm...you mean, to cut off the internal drive and just use the external?
Nope, not yet - worth a try