Dead Apple IIe

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Dead Apple IIe

Looking for some advice.

 

I have an Apple IIe which is completely dead.

I have tested what components I can and found 3 faulty logic chips, 3 faulty ROMs and a suspect CPU. I replaced all of these , but still can't get any video output, nor do I get a beep with Ctrl G. 

I have checked the clock which is OK, but the CPU reset doesn't seem to be working properly - a scope on Pin 40 of the CPU shows a high signal with a fair bit of noise and this doesn't go low when the reset key is pressed.

According to my understanding of the circuit, the most likely component to have failed is the Input/ Outpu Unit IC which in this machine is a 344-0022A (though the board is marked 343-0022), but I can't find a decent schematic to be sure I'm not missing something obvious.

Unfortunately I can't find a supplier for this chip (I'm in the UK), so would appreciate any tips as to where to obtain one, or help in diagnosing the real problem if I'm wrong about this chip being faulty.

I should add that I've tested all the RAM and that is all good.

 

Thanks for any help.

 

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Hi there, I'm not an expert

Hi there,

 

I'm not an expert but looking on my schematics the Reset line seems to come from the IOU pin 15? Now, I do not know what the conditions are for that reset line to go low to be honest, I can have a look on what I have which is what I found online, nothing special. On the Apple //e repair guide I do not see the IOU as a possible issue for boot-up problems to be honest.

The flow chart I found on another repair guide seems to indicate that the reset line should be pulsing immediately after the clock starts. 

 

When you say  "reset is pressed", do you actually mean pressing the reset button on its own? AFAIK that doesn't do anything. To reset the system it's CTRL-Open Apple-Reset. Sorry if you already know that :) 

 

What part of the UK are you from? I live in the UK too and have an Apple //e too.

 

 

 

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Just checking the basics

Hi Graham,

I assume you've checked the power rails are delivering the right voltage? I have a IIe I can check things on if it'll help. I assume yours is a PAL unit if you're in the UK? (Same as mine?)

 

Chesh

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 I used to repair computers

 

I used to repair computers for a living, and still do a few repairs more as a hobby than anything else, but I've only ever worked on 2 Apples II machines in 50 years! In both previous cases the faults were due to faulty ROMs, so I've no real experience in what to expect on these and am relying mainly on a SAMs book that I found online plus generic experience repairing 8-bit machines.

I did check the power supply (and replaced the RIFA capacitors) and as all the ICs are socketed it made sense to just check all the logic, RAM etc. The custom chips, though, are a bit of a mystery to me and I couldn't find anything that would tell me what to expect. 

When I switch on, the monitor picks up a signal (at least it switches to composite video mode), but I just get a black screen with no output at all.

 

Thanks

 

 

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Graham, Is there any other

Graham,

 

Is there any other activity happening? Does it beep when you power up, does the drive spin?

Re-reading your message you say "Input/Output Unit" which I guess it's the IOU I mentioned above. But, again, I am the least prepared person on //e on this forum so please take my advice with a pinch of salt. 

 

From the schematics it seems that the RESET line only goes from the IOU to the 6502, maybe that could confirmed by following the trace. You could try removing the CPU and checking the RESET line to see if it behaves - no idea whether the reset signal would work without a CPU though. The other way would be to bend the RESET line on the IOU so it does not go in the socket and test again but considering that the IOU are hard to find, I'll leave that decision to you.

 

Do you see any data on the address/IO lines of the CPU? I guess not but worth checking. 

 

The RESET line also goes to all the card connectors so I would also remove the disk controller in case it's causing issues - you should still see "Apple //e" and hear a beep on screen regardless I believe. 

Other thing I would do is to check that all chips got supply voltage and ground - but you probably know that already. 

 

You didn't reply to my question about the RESET button! :) 

 

 

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Sorry - I missed that. I

Sorry - I missed that.

 

I think I just pressed the reset switch, so I'll try again - though it won't be until tomorrow now before I can get back to it. I'll check that connection as well - do you know which pin it goes to on the IOU? Unfortunately I still haven't been able to find a schematic  for this model (at least not one I can actually read!)

I removed all the add on cards including the floppy disk controller, but I don't have a suitable drive here anyway at the moment.

There is some activity on the data lines, though one of them is vastly different from the others. I checked the power supply, but I don't think I tested all the power connections on every chip, though I did check the RAM and the logic chips.

I am a bit wary of bending the pins on the IOU, but may take a chance if I've ruled everything else out - I just have that feeling in the back of my mind that I've missed something.

 

Thanks

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Yes, the RESET key on its own

Yes, the RESET key on its own doesn't do anything. To be honest I would power cycle the machine when you test.

 

For documentation I was pointed to this FTP link: Index of /pub/apple_II/documentation/hardware/ (asimov.net)

The schematics I am looking at is called "Schematics Diagram of the Apple IIe.pdf". Even if boards are different, I suspect the IOU is always the same chip so you can trust the pinout of any schematics. On the one I have the RESET line comes out of pin 15 of the IOU and gets into pin 40 of the CPU.

 

Totally understand that bending a pin of a hard-to-find chip is not the first thing you may wanna do. What you could do is to use another chip socket - and cut pin 15 of it. That way you should be able to see whether the RESET line works ok when the IOU is not connected to anything on that pin. Again, this could be a dead end. And if I understand correctly the RESET line would only go low for a moment to reset the CPU. 

The vastly different data line may be a clue as well. I was watching a video from - I think - Adrian Black the other day and he mentioned that the CPU "HALT" pin can be used to stop the system whenever something is wrong. It can be triggered by something on the board or by the CPU itself - if it detects bus contention for example. How does your HALT line look?

 

I wouldn't worry about the disk drives: if you do not get an "Apple //e" or "Apple ][" on screen and a BEEP, it won't matter :) 

 

Checking the supply AND ground on every chip is something I normally do - I got that lesson after struggling with an old cinema sound processor for a while to then realise that the GROUND pin of the RS232 chip was not connected, making internal serial communication not possible. 

 

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The /RESET signal is an input

The /RESET signal is an input to the CPU, an output from the keyboard and bidirectional connected to the slots and the IOU. There is no external  pullup, AFAIK. Means the IOU generates the power-on /RESET and has an integrated pullup. Typically there is another /RESET source: the disk II controller.

 

There are different IOU chips available, see https://kb.pocnet.net/wiki/Apple_Chip-Bezeichnungen . But I believe that the /RESET is always the same.

 

Hint: the informations in that  table are not completely confirmed. If there are more please tell me :-)

 

Regards

Ralf

 

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