Mac Pro - RAM disappearing, showing wrong capacity

Hey,

I've got a 2008 dual quad-core Mac Pro running 10.8.

The RAM is disappearing, and changing capacity when I check it. Also some DIMMs are failing the power on test.

This morning when I booted up it was showing 2x4GB modules and 2x2GB modules, which I thought was weird because I was certain I had at least 16GB of RAM. Later this evening I restarted and now it's going 4x4GB modules again.

In the morning System Profile said two RAM modules (one in Riser B, one in Riser A/DIMM 4) had failed the power on test. Now in the evening, only the one in Riser A is showing up.

The "About this Mac" and "Memory section in System Profile" show that Riser A/DIMM 4 is empty.

It's a touch confusing. Why would the capacities be fluctuating? Is this bad RAM, or possibly bad Risers?

I'm thinking I should run an AHT and see what that turns up.

Currently looking up replacement modules on OWC, and well boy it's pricier than I remember.

Any input would be appreciated.
Cheers

Gav Mack said:

Take out the riser cards and blow everything out with a can of compressed air.

Forget about buying new FB-DIMM's as the prices are so extortionate, new parts are increasingly rare so more expensive and 10.9 should be the last OSX it will support so not worth breaking the bank for them. Buy used modules off eBay with 14 day return option so you can hammer them with tests to see if they are ok or not.

Click to expand...

Thanks for the advice I'll give that a go.