Can a memory channel go bad?

[gbrayjr]

I bought an EP43-DS3L and originally put in 2x2GB Memory sticks in Channel 0.  I used matched Patriot DDR2 1066, 5-5-5-15 (PDCG248500ELKR2) at the default speeds/BIOS configs.

Everything worked just fine.  Then I decided I needed 8GB, so I tried to track down another 2 sticks of the same memory.  I found the Patriot Viper PV224G8500ELDB at Fry's, which is also DDR2 1066 5-5-5-15.  It has a different packaging/heatshield, but I figured it wouldn't be a problem, since it's another matched set running in another channel, but still with exactly the same timing specs.

Because of clearances with my CPU heat sink, I couldn't fit the new memory in channel 1 (the Viper memory has heat sink fins).  
I put the ORIGINAL memory in channel 1, the NEW memory in channel 0.  The mobo recognized 8GB, but then immediately boot-looped when starting Windows. I suspected bad memory or issues with the (slightly) different memory sticks in each channel, so started troubleshooting.

I took out the NEW memory - put the ORIGINAL memory back in channel 0 - the machine boots/starts fine with 4GB.  [phew...that's where I started]
I took out the ORIGINAL memory - put the NEW memory in channel 0 - the machine boots/starts fine with 4GB of the new memory [curious... seems like both sets of memory work in channel 0]
Then, I put the ORIGINAL memory in channel 1, with channel 0 empty.  the machine boot loops.

Basically, any time I have somtthing in channel 1, it's unstable, even though both pairs work fine in channel 0.  If I'm lucky, I can get to the BIOS, but not reliably when any memory is in channel 1.

Suggestions?

[oggmonster]

Possibly, try running a memtest only indivudual sticks and different slots (tedious I know) Also if all 4 ram slots are being use you may have to bump up northbridge volts and maybe even manually set RAM volts/timings etc.

[gbrayjr]

Thanks for the suggestion.  I ran memtest with the same memory stick in multiple slots... Here's what I'm seeing

Original memory in dual channel mode:  [2GB in Slot DDR2_1, 2GB in Slot DDR2_3]   Memtest passes 100%

Then I took the same stick of memory and moved it from slot to slot.
1) Passes:   Original memory in single channel mode:  [2GB in DDR2_1]   Memtest passes 100%
2) Fails:  Original memory in single channel mode:  [2GB in DDR2_2]   Memtest fails immediately.  Within a short time, memtest terminates with an exception.
3) Passes:   Original memory in single channel mode:  [2GB in DDR2_3]   Memtest passes 100%
4) Fails:  Original memory in single channel mode:  [2GB in DDR2_4]   Memtest fails, but not as quickly as in slot DDR2_3.  after 50% of the tests, there were a handful of errors.

Grrr... is this a defective motherboard?   I guess it's not the memory channel technically, since I'm running in dual channel mode with slots 1-3.  It's the 2nd and 4th memory slots.  The yellow pair of slots (1,3) which were originally populated w/ 4GB work fine.  The red pair of slots (2,4) seems to be hosed.  Anyone seen this before?  What a bummer of a hidden defect.