Troubleshooting Plan, looking for opinions

[JustKJ]

I have a Apple iMac Aug 2020 with 128 GB of Crucial RAM (4 x 32GB sticks). I the past 10 days, my Mac has had an increasing number of CPU Panics (hard crash). I assumed it was not the RAM as it wS installed for the start and worked for 6 weeks with no issue. I added a USB Dock and a second monitor. About 2 weeks ago, so I have been removing hardware and limiting the Apps I have been using to see if I could eliminate the problem. It keeps happening, so now I am looking at the RAM as a potential cause.

i created the bootable USB and fired off the test. It cooked along To 70% of test 3 and had a string of 2500ish errors in a row. But then kept going, it hit 70% of test 4 and and Another string of Until is hit 10,000 and it aborted.

I am rerunning it as I write this with CPU set to round robin (don’t know why I picked that, but I did). It hit the same 70% of test 3 and had half as many errors, same with test 4. Test 5 hit 70% and th string of errors continues until it passed 10K and aborted again.

Assuming these errors are bad RAM, here is my plan to isolate the stick:
remove all but 1 stick and retest.
if clean, add back one stick at a time and retest.
once I find the bad stick, reinstall the rest and test one final time.

is there any way for a quasi-techie to know which the bad stick it base on the pictures below?

[JustKJ]

An update...I pulled slots 2,3, and 4 and ran the test on the first stick only. It has a string of errors like the above pictures, at pass three and four and it aborted. I swapped stick 2 into slot 1 and that program is currently at test 13 with no errors. But wow...2 hours and counting.

would I be safe in assuming I found the faulty stick, if I can get the last 2 to complete at least through step 4? And then reassemble the three sticks and run the test a final time as a whole?

yes, I agree it would be more thorough, but I have an all day zoom training class to deliver and I need to finish up the testing today.

[David (PassMark)]

There isn't any easy way to know which stick is at fault from the memory address. Dual channel memory interleaving and similar stuff make this nearly impossible to work out.

But wow...2 hours and counting

You have a lot of RAM in the box. So testing will be slow. Very few apps will actually use 128GB of RAM and MacOS will run fine on a single stick of RAM. So you could do that for a day.
You might want to run on two sticks and not three, as running with three will probably drop the system out of dual channel mode. It depends how much you really use of your 128GB vs how much you value the slight performance increase.

[JustKJ]

Thanks for responding. I have test all 4 sticks and the first horribly failed and the other three took 2 hour each, but passed all 13 with no errors! I contacted Crucial for a free replacement of the faulty stick. Just for grins I am rerunning the test with all three good sticks installed. I may cancel it before the Hammer Test as they all three passed that individually.

You might want to run on two sticks and not three, as running with three will probably drop the system out of dual channel mode.

I contacted tier 2 of apple support (I had a directly link past the entry tier). The support person said that Apple does not endorse MemTest, but unofficially she uses it and had great things to say. I asked that exact question about duel channel and if I should just put two (all in one channel or one per channel) and she said said it would operate fine in any configuration. The Balancing was key if you you were using different amounts per stick, then you should try to balance the channels.

Either way it should take about 10 days for the replacement. So even if it is slight degraded, I will be fine.

The reasons for the large amount of RAM were 1. I teach a teach a course on time management the uses outlook as a tool. I have Parallels to create Virtual Machines. So I present and run the event from the Mac OS and may have up to three VMs running at one time so that I can show three different versions of outlook depending on the need and questions.