Classic Sad Mac: RAM Error?

[LaPorta]

Hello,

A Classic that I gave to my nephew a while back has started to exhibit sad Mac error code 0000000E/00000200. My Mac Repair Book indicates that this should be some sort of RAM issue, and per the book (which is not Classic-specific) it should be Bank A of the RAM, and I think the second line indicates an issue with a particular chip. I cannot rule out other issues: this has been re-capped, and I cleaned it pretty thoroughly but I would not rule out some sort of electrical gremlins or something. I removed the RAM expansion card, and that proved to not be the issue. There was a trace that appeared corroded (the one just north of UH6 that connects between G1 and the SWIM. I traced that down as a ground trace, and I thought the pin on UH6 closest to it was shorting to it, since I got a slight chirp between ground and that pin, which I was unable to reproduce on another Classic board. So, I cut the trace on either side of where it runs past the pin on UH6, and bypassed it with a wire patch...and the same thing occurs. I cannot explain the instantaneous chirp that goes away when buzzing out the trace. I may be chasing a red herring here. The machine otherwise worked just fine until this crept up. At this point, I am pretty much out of ideas as to what might be going on here.

 

[LaPorta]

Anyone have any insight here?

 

[cheesestraws]

I cannot explain the instantaneous chirp that goes away when buzzing out the trace.

Capacitance between A and B?  Current flows to charge the cap(s) just long enough to trip the buzzer then stops

 

[LaPorta]

Yes, that is possible, the interesting thing is that id=t doesn't do it on the same trace on another board.

 

[LaPorta]

Hi everyone, I am restarting this thread, as I am back at it for my nephew. The exact error code that the machine displays when started is:

0000000E
00000200

Reading one of the Mac Repair Manuals, it states that this is a failed data bus test. The second line indicates the bad bit "as a 32-bit mask for bits 0-31" Granted, I have no idea how to translate the second line into something meaningful...or to indicate if that is a bad RAM chip, or, perhaps, just a bad trace somewhere. Anyone else run into this before, or know what to look for?

I will also say that this just started happening to the machine out of nowhere three years ago (I've had it in storage since then). Both AB and LB were recapped and it worked just fine until doing this out of nowhere.

 

[ymk]

I think 00000200 points to the D9 line.

 

[LaPorta]

I think 00000200 points to the D9 line.

How does one ascertain that? I'll look for any intermittent connections.

 

[ymk]

Convert the hex value to binary:

00000000 00000000 00000010 00000000

The leftmost zero is bit 31 and the rightmost is bit 0. The one corresponds to bit 9 / D9.

 

[LaPorta]

now to just find out what might be wrong along that line....maybe its the RAM chip itself. The schematics show that the RAM chip at UK4 has a pin that travels along D9.

 

[LaPorta]

I do have another Classic board that appears to have a simpler error:

00000003
00000002

That appears to be a RAM test error, and if I did the conversion right, it means chip 2 is bad...which I assume is UK2. Can anyone confirm this? I guess I can use hot air and swap out a chip from the other board to this one.

 

[ymk]

00000002 points to D1, which belongs to UK7 and UK8.

 

[LaPorta]

But the error is different. The “03” error in the book doesn’t point to data bus lines, it points to an actual RAM chip testing bad.

 

[joshc]

There isn't too much that can be wrong. It's either bad RAM chips or bad traces to/from the RAM chips. Those chips are cheap and easy enough to source that I'd just start with replacing all of them. A bit more soldering work but not too hard.

 

[LaPorta]

There isn't too much that can be wrong. It's either bad RAM chips or bad traces to/from the RAM chips. Those chips are cheap and easy enough to source that I'd just start with replacing all of them. A bit more soldering work but not too hard.

Maybe the shotgun approach makes the most sense then.

 

[ymk]

But the error is different. The “03” error in the book doesn’t point to data bus lines, it points to an actual RAM chip testing bad.

If this is the case, then the error code

00000003
00040000

as seen in this thread shouldn't be possible.

I'm not entirely sure, but 00040000 looks like a mask to me.

 

[LaPorta]

Ok, it looks like this is more complex than I thought. Using two different sources, it appears that $0003 does indicate a RAM test failure in Bank B (not sure what counts as Bank B when there are no banks on the Classic...I have yet to figure out if there are Classic-specific codes, but I cannot seem to find any either in books on on the net). There is no RAM expansion card installed. An example from a book I have stated that if two bits fail, their summed values are displayed on the second line. Since that thread you pointed two noted that both UK1 and UK2 chips were bad...so it is possible that the summation equaled what was displayed? With my code, how do I figure out where the bit that failed lies?

 

[ymk]

In the thread I linked, UK1 and UK2 share data lines 12-15. He narrowed it down to a single data line and replaced both chips, but it's likely only one was bad.

What I don't get is that 00040000 indicates a failure in the upper 16 bits of the data bus, which the Classic doesn't have. Maybe the code is a typo.

Like I wrote in this post, convert your error code to binary and count which column the 1 appears in. D0 is the rightmost column.

A D15 failure would produce the code 00008000.
A D13 failure would produce the code 00002000.

If both of these data lines failed, you'd get the sum, which is 0000A000.

 

[LaPorta]

Code is 00000002. Converting it gives 00000000000000000000000000000010...so D2? If I read the schematic right, D2 comes from UK8?

 

[ymk]

It's D1. The first column on the right is D0.

D1 runs through UK7 and UK8.

 

[LaPorta]

Well...here go UK7 and UK8 out the door!