Almost a working IIc, advice needed

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Almost a working IIc, advice needed

Hey all, an Apple newbie here.

I took up checking my uncle's Apple IIc, that's spent the last 30-35 years in a cupboard.

The computer's actually in a pretty good shape, it's got the monitor, the stand and an external disk drive. All apparently in working order even after all these years. It's a PAL machine with the original 255 ROM.

There are several 5.25" disks in multiple formats. A few original Apple disks and the rest are copies.

The problem is the computer won't boot anything but DOS3.3 or custom bootloader disks (as far as I understand). PRODOS disks get stuck in the screen where it says "PRODOS <version numbers>" with a message saying "** Unable to load basic.system **" (or whatever .system file the disk is trying to boot). Pascal disks get stuck in a black screen a couple of seconds into the boot. Mission Impossible also loads for a few seconds and gets to the title screen, but then just stops loading and just sits there. I've managed to get a few simple games to work, for example Dig Dug.

I've cleaned the drives, tried booting from the external drive, swapped the external drive with the internal one, adjusted the drive speed (for some reason I can boot the Locksmith 5.0 disk and use the drive speed calibration program), popped out all socketed chips,  cleaned their pins with IPA and reseated them, measured the power supply (+18V with no load and +16V when the computer's running) and gone through all the disks. All the PRODOS disks are unable to boot in both drives, so I don't think it's the disks or the drives that are faulty.

I made an ADTPro serial cable and was able to bootstrap the ADTPro software, but when I tried to receive a disk image, the transfer gets stuck on either the first block or the fifth.

I started the machine with no disk, did the ctrl-reset thing, and tried the serial cable by running IN#2 and PR#2 commands (with the ctrl-A ##B to set the bit rate). I was able to write perfectly fine from the PCs terminal program and the letters appeared on the IIc's screen. When I tried it the other way around and typed on the IIc, the PC only got garbled text with accented letters, e.g. "ÉÁÓÍÁ" and so on. No matter what bps, parity or stop bits I used, I never got correct letters when typing from the IIc to the PC.

There's one more constant symptom, that's appearing in several situations: four pixels in a vertical formation, like two : -characters on top of each other. They're always in the same place, in the lower left quadrant of the screen, sometimes even when a program is running.

Since I've done everything I can think of outside of replacing chips or other components, I'm in need of advice.

Could these symptoms be caused by failed RAM chips? They're all MT 4264-15's, which are prone to failing, if I've understood correctly. Or could there be a fault somewhere else?

So far nothing I've done hasn't made the IIc work any better or any worse, so at least the problem is constant.

Thanks in advance!

 

 

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Apologies if I missed this in

Apologies if I missed this in your post...but did you try the self-test?  Apparently it tends to run forever with the 255 ROM but might give you some useful info?

https://retrocomputing.stackexchange.com/questions/14886/how-long-should-i-expect-the-apple-iic-self-test-to-run

 

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Self-test?

Certainly could be a RAM issue - the issue with the invalid characters in a vertical line is suspicious. Could also be a logic issue with an address line, but a defect RAM is much more likely.

You didn't mention the result of the self-test. Does the self-test work fine or report issues... Did you run it? :-)=> Open Apple + Closed Apple + Ctrl + Reset.

And welcome to the forum, Nonsensei-san!

 

Edit: haha, monkmaniac was quicker with the same question. I should have reloaded the page before commenting...

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AFAIK on a 255 that "self

AFAIK on a 255 that "self test" doesn't really do anything or give you any indication of a fault.

 

 

Lacking a bootable diagnostic disk, there is always the finger test. Bad ram chips tend to run noticeably hotter than their functioning counter part. 

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Thanks for the replies!Yes,

Thanks for the replies!

Yes, unfortunately the self-test on a 255 ROM just displays wavy patterns on screen indefinitely, and doesn't really test anything.

Since I'm unable to boot almost anything OR write images on disk, I can't use any diagnostics disks. I do have a C64 and a DOS PC with 5.25" drives, but from what I understand, neither are capable of writing Apple disk images.

The only way to get to a diagnostics program would be to somehow make ADTPro bootstrap a diagnostics disk instead of the ADTPro program, but I haven't gotten that far yet.

None of the RAM chips feel significantly hotter than the others. The GLU and TMG chips get a bit hot, but I don't know if that's normal.

My next move would be piggy-backing new RAM chips on the old ones, but that's another challenge. The only chips even close to the 4264-15's I'm able to source locally are KM 4164B-15's, and I have no idea if they're compatible.

 

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Here is a list of 4164 part

Here is a list of 4164 part numbers.  Basically you want to make sure they are 150ns.

 

 

As noted on the list, Micron decided to label theirs 4264, even though they are really 4164. Based on the replacement  part number you provided, those are 150ns Samsung chips and should be fine. 

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That's great, thank you! I'll

That's great, thank you! I'll order a few RAM chips and see if that gets me anywhere. I really appreciate the help!

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I got the memory chips today.

I got the memory chips today. After testing I found out, that at least of the IIc's memory chips is bad. When I have a new chip piggybacked on MRD5, the computer boots PRODOS disks and I was able to transfer and write a disk image with ADTPro.

I have a hunch there's at least one other flaky memory chip on the board. It would help a bunch to have a memory test program of some sort, but I can't figure out what program would work. There are a bunch of diagnostics disk images on Asimov in /images/disk_utils/diagnostics/ , but I haven't got the faintest idea which ones are good and/or work with the IIc.

Any suggestions?

 

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Good news everybody!I tried a

Good news everybody!

I tried a couple of programs and finally settled on XPS Diagnostics 1.0.5. It confirmed that the chip on MRD5 was defective.

I desoldered the chip and put a new chip in, and there it is. XPS Diagnostics is no longer reporting errors.

That's at least one problem down, now I have to start testing everything all over and seeing if there is something else wrong.

Thanks a million for the help!

 

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