Apple IIc Logic Board Problem

Hurry

Hurry

Tinkerer
Oct 28, 2021
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Good evening! I’m trying to track down a couple of faults on an Apple IIc and I think I’ve hit the limit of what I know how to do. I try not to ask for help until I hit the point where I either don’t get useful Google results, or I don’t know how to construct my query to get results.

Thankfully I have two Apple IIcs to work with and swap parts. Let me take you through the symptoms and what I have done to troubleshoot so far.

Symptom 1: Internal Floppy Doesn’t Work

When I insert a disk and boot, the drive spins up. Depending on the type of disk, a variety of different things will happen but never success – Unable to read ProDOS, blank screen, infinite red drive light and spinning, etc.

Symptom 2: The Dot

I’m mentioning this because it could be related. There’s a dot on the center of the screen when I boot the Apple IIc. If I carriage return, the dot stays and a new one appears above it, though the one in the center is always brightest.

What I’ve done so far
  • I’ve tested the Apple IIc on three different monitors, “The Dot” follows the computer.
  • I scrubbed down the logic board and reseated the five socketed chips after thorough cleaning. None of the few caps look bad. No change.
  • I replaced the floppy drive from the bad Apple with a known good one – same symptoms. If I put the bad Apple’s floppy in the good Apple, it works as expected.
  • I patched a Floppy EMU to the disk drive port on the bad Apple IIc and can’t load a disk. Sometimes it hangs on Track 00, sometimes it will even advance to Track 01, but nothing ever happens.
  • I then proceeded to swap every other part I could – the five ICs, and even the power supply. No change.
My conclusion is that I have a problem on the logic board somewhere – possibly related to the drive controller but maybe it’s higher level if the dot is related. My other problem is that I don’t know how to read schematics and I’m not someone who can point at an Apple II logic board and identify the chips and what they do. Before I start trying to test continuity on every damn trace on the board – does anyone have any hints or anecdotal experiences that might help me narrow where I should be looking for a fault?

As always, thanks in advance!
 
AndyDiags

AndyDiags

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Dec 18, 2021
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Does it make the sound on boot?

Perhaps a bad ram chip, I believe I’ve seen a video recently where someone mentioned that a specific brand of ram on these are prone to failure.

It may help to post a high quality image of the board.
 
Hurry

Hurry

Tinkerer
Oct 28, 2021
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I was wondering if it might be memory related. It does beep when powered on.

IMG_6043.JPG
 
AndyDiags

AndyDiags

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Dec 18, 2021
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Your ram is made my Micron Technology (MT). Here and here, which have discussions on IIc ram failures, the same ram brand is present.
Your board was made 36th week of '84. My IIc which is same board revision was made several week earlier in week 22nd of '84, and my ram is OKI, made in Japan. Maybe they switched to a cheaper more problematic ram.

It looks like your IIc has the original ROM revision, which I don't think has the ram self-test build into the ROM. Perhaps your other IIc you mentioned has a newer ROM. As mentioned in this article, if you power on with a newer ram and no keyboard attached, the board will run a ram self-test.

One other question, what happens when you currently turn on your board w/o a keyboard? Do you see the dot or do you see the random pattern?
 
Hurry

Hurry

Tinkerer
Oct 28, 2021
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Unfortunately both of my IIcs are original 255 ROMs. If I power on without the keyboard attached, I see three smaller dots flickering in the center of the screen. I didn't know that was worth trying, thanks for mentioning it. I was thinking about picking up a 4x ROM for the good one - maybe I'll do that and shelve this until I can do the the self diagnostic once I have one to play with.
 
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Daniel Hansen

Daniel Hansen

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Oct 29, 2021
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The MECC diagnostics tool has a decent RAM test (https://macgui.com/downloads/?file_id=9613). It won't tell you exactly which chip may be an issue, but it will at least isolate it to either the main or aux bank. And then you'll know it's indeed a RAM issue (it seems like it to me fwiw).

ROM 4X is also a route to explore, as it contains a IIe style diagnostic that will tell exactly which chip is having a problem (though it stops when it encounters an error, and often more than one chip is problematic). And its benefits are multiple. (Edit: sorry, I see this has been suggested already!)
 
Hurry

Hurry

Tinkerer
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I hoped to run the MECC diagnostic test but I can't get this to boot to any disk or Floppy Emu, unfortunately.
 
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AndyDiags

AndyDiags

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beeblebrox said:
I was thinking about picking up a 4x ROM for the good one - maybe I'll do that and shelve this until I can do the the self diagnostic once I have one to play with.
Click to expand...
Just gives you an extra reason to pick one up now. This may help you narrow down if it's the ram or something else.
I'll actually put in order a chip for myself right now so I also can go ahead and update my ROM as well.

if you have a signal analyzer, you can also compare the output of the ram and other chips to your working board to maybe help you further narrow own the issue.
 
Hurry

Hurry

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AndyDiags said:
Just gives you an extra reason to pick one up now. This may help you narrow down if it's the ram or something else.
I'll actually put in order a chip for myself right now so I also can go ahead and update my ROM as well.

if you have a signal analyzer, you can also compare the output of the ram and other chips to your working board to maybe help you further narrow own the issue.
Click to expand...
Signal analyzer is out of my realm of experience. At some point maybe the job will come when I'll take that as an excuse to make it part of my experience - but I think for this I'll start with the ROM 4x.

For curiosity's sake, when you asked about the keyboard, were you attempting to determine if the keyboard might be sending the dot signal? While I now have that in my mental inventory of things to try (it didn't occur to me to swap keyboards), I'm interested to know your thinking.
 
Daniel Hansen

Daniel Hansen

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Oct 29, 2021
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beeblebrox said:
Sorry - it's not the image. It's the fundamental problem I'm troubleshooting. Neither of two known working floppy drives or the Floppy Emu using known working floppy discs or images will boot the machine.
Click to expand...
Ah right - apologies - I clearly scanned right past key parts of your original post... 😬 I'm on a roll.

Other than verifying the floppy cable is good, you're into typical board-level diagnostics now since isn't any easy way to isolate the issue based on these symptoms - it could be I/O related, it could be deeper... echoing @beeblebrox the 4X ROM is going to your friend as at least it will allow you to run the diag, or boot off the external drive or device (possibly depending on what the root cause actually is), or least drop into monitor and verify some basic operation (again, depending).
 
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Daniel Hansen

Daniel Hansen

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beeblebrox said:
For curiosity's sake, when you asked about the keyboard, were you attempting to determine if the keyboard might be sending the dot signal? While I now have that in my mental inventory of things to try (it didn't occur to me to swap keyboards), I'm interested to know your thinking.
Click to expand...
Booting without the keyboard will display a test pattern.

EDIT: Further clarification... later ROM versions would run a diagnostic test if you booted without the keyboard attached, but 255 ROM's don't do this... instead it just runs a cycling test pattern that doesn't really tell you anything... unless something to totally busted. Swapping the keyboard wouldn't make a difference, as the character ROM is on the logic board and independent of the keyboard: the position and behaviour of the dot you describe strongly suggests a RAM issue to me.
 
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AndyDiags

AndyDiags

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desertrout said:
Booting without the keyboard will display a test pattern
Click to expand...
Exactly! And you're not seeing that pattern. That kinda makes me thing it may not be the ram.
You should look into what the pattern means for that first rom. For example, do we expect the pattern to appear even with a bad ram? If so, your issue may be elsewhere.
 
Hurry

Hurry

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Okay - understood. I tried multiple times and did see what might want to be a test pattern, but it wasn't very organized. And each time I hard booted, I saw a different image until I saw the black screen with three smaller flickering dots in the center.
 
Javmast3r

Javmast3r

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Oct 27, 2021
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You got a ROM 255. Sounds like you have a RAM problem, I would start by replacing all Main RAM chips (MRD 0-7). Also, could be the IWM that is bad, but most likely just RAM. To test, you need to upgrade the ROM to 0 or above, and do open apple - closed apple - control - reset to enable self test.
Like mentioned, the MT RAM is the worst, and you should replace it anyway.
 
Hurry

Hurry

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ROM 4X came today. Sure enough, (Main RAM) RAM 00000010 error on system test. Have replacement chips and low profile sockets on order. Seeing the light at the end of the tunnel.
 
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Javmast3r

Javmast3r

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Careful with the sockets. I replaced all in one and then the computer crashed when was closed, as the drive pushed the chips and caused issues.
 
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