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Mac 128 error 0488DC

Macdrone

Macdrone

68020
Ok so I go online and lookup the sad Mac error code and it says 04 is a memory failure, 8 8 being the locations or what, and no breakdown of the DC. I put in Mac plus roms and it changed to 0388DC. So it just checks the memory in a different order I'm thinking. This is an unmolested 128, so should I replace the caps first (as there are stray dots on the screen at turn on) and maybe all the issues go away, if not then see if code changes and repai from there. I am trying to keep it as unmolestec as possible as I don't think it was ever used. A lady named Pam from Seattle has been unloading her fathers stuff to me for over a year now as she finds it. I am thinking he got the plus as soon as it came out and never even used the 128. There is not even lint inside at all.

Serial number is F42567QM0001 for those decoders out there.

Came with the 400k external that I didn't have yet.

Would have posted in conquests but want to fix it first.

 
The leading 04 indicates it is a memory test failure. It is my understanding that the subsequent digits are a bitmask identifying which chips are bad. Typically you see just one bit set, so would hit something like 048000 for the chip located at G12 on the logic board. If you've got multiple chips bad, each bad chip sets a bit in the error code, so 0488DC would be chips G12, G8, F12, F11, F9, F8, and F7.

That's almost half the RAM chips, so I'm going to suspect it's not actually the RAM that's bad, but something else causing the RAM test to report the RAM as bad, like the power power from the analog board or something. So caps might be a good place to start.

 
Ok recapped the board, since there are only three. Put it back in and exact same result. Dotted vertical lines (more dots than looking like lines. Of course code didn't change.

So would bad ram issue cause dots and the bad ram check. It is my first run in where caps made no change at all.

If the ram is the issue I'm not exactly sure how to tell which ones exactly laid out are which. Really would be a shame to lose apple branded memory chips, but I would love to get the board working.

 
The logic board should have letters on one side and numbers on another, so you can identify regions of the board by the intersection of the two. The locations I gave below should correspond to this grid system.

One non-destructive test you can do for the memory is to just overlay a suspect RAM chip with a known good one. Just be sure to get the correct orientation. Just piggyback the good one on the suspect chip, and see if that makes a difference. It's not quite the same as replacing the chip. If putting the good one on the bad one works, you know the bad one really is bad. If putting the good one on the bad one doesn't work, it doesn't really tell you much. But at least it is non-destructive.

 
Oh did I mention my other 128 board and plus board work with this analog board? I guess I'll get some memory chips, as I don't have any yet and try that.

Thank you bBraun.

 
Well sure enough I found the maybe culprit inside the case. A small shiny metal screw just floating around. Who know what it shorted out on the motherboard. I ordered some ram chips as it was only a few dollars and well see if that fixes it with the piggyback method. If not I may just be out of luck.

 
Ram piggy backed no change. Im sad. Anything could be bad at thi point. Caps and memory didnt make a difference, roms didnt make a difference othe than changing the 04 to an 03, which is still a memory error. Looks like I have a beautiful 128 case with a dead motherboard. Was hoping to use a non upgraded board but oh well I guess.

 
Have you verified all the traces that run between the Ram chips ? A broken trace can also give these Sad Mac ram errors.

 
Piggybacking new memory chips changed nothing. Changing roms changes the 04 to 03 which is still a memory error. I think something else on the board is the issue. My eyesight even with a magnifying glass checking traces isn't gonna get me anywhere but the board looks brand new, minus the caps I replaced. With a 512 and 128 board from my others in there the mac boots from floppy and screen has no burn and is sharp and bright.

 
Had a over eventful month in a bad way with some close family passing. I am still kinda rough about it all but I am back.

 
Nothing, board is dead, replacement chips did nothing. A good board would be the only thing that saves this dead one.

 
Ill send it but I changed the roms, piggy backed the ram so something more than I have parts for need changed. I rigged in replacement capacitors, looks ugly but correct values so that did nothing. Board didn't even have dust on it. Like I said looked like it had never been used. The only thing I wanted it for was to say I had a unmolested, non upgraded board and I already botched that with the caps.

 
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