[X4U] DRAM failure (was Hard drive or hard drive controller gone)

[Jim Robertson]

Continuing my lamentations over my son's sick Mirrored Drive Doors G4:

A new hard drive didn't solve all the problems. The computer continued
freezing up unpredictably (no Kernal Panic, no warning, just a frozen mouse
cursor and no response to any keyboard or other input).

I downloaded memtest and ran it in single user mode. It appeared to indicate
TWO separate addresses that generated errors. So, I've swapped the modules
in and out, and the original 256 Mbyte stick from Apple seemed OK (although
the computer won't even boot if this DRAM module is alone in the slot
immediately adjacent to the processor heatsink).

I tried moving the Apple stick into the second slot (nothing in the other
slots), and the machine passed multiple memtest runs. So, I decided one of
the two 512 Mbyte modules must be bad, and thought it wouldn't take long to
sort out which one was faulty. I put one of them back in slot 3 along with
the Apple module in slot 2, and once again memtest reported errors.
Curiously, they were now all at ONE address offset, not two.

I took out the "bad" DRAM 512 Mbyte module, put in the other, and thought at
first I'd solved my son's problems, because I went through one complete pass
of the memtest routine with no errors reported. Unfortunately, the 2nd and
3rd passes reported errors, though not as frequently as with the other 512
Mbyte DRAM module installed. And, they were all at one address offset, and
DIFFERENT from that had been reported with the other module installed in the
same location

So, I now believe the results are consistent with a bad address on each of
the two large DRAM modules, but now I'm wondering WHY all these problems are
showing up at once (especially since the machine wouldn't even boot with the
good Apple-supplied module sitting by itself right next to the processor).

So, I downloaded temperature monitor 3.2. It reports only two readings in
this machine, at the "B" CPU and at the hard drive, and they seem pretty
hot. The CPU is 57.5 degrees celsius, and the drive about 40-42 degrees
celsius. The fans seem to work normally and cycle up and down in speed.

So, I have three questions:

1. Is it likely I'm interpreting the memtest results correctly? (two address
offset errors reported when there are three modules installed, none when
only the Apple 256 Mbyte module is in, and one address error reported when
either of the two 512 MByte modules is added to the 256, implying a bad
address on EACH of the two modules?)

2. Is heat in the machine killing drives and DRAM modules?

3. How many of you would plunk down $75 for replacement DRAM for this box
(considering that I've already invested $100 for a new 300 Gbyte ATA drive
that I cannot use in any other Mac in my house)?

Thanks so much,

Jim Robertson
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