Hi Don and welcome.
We have had this question before and we tried to get an answer from Sony. Their reply was that it supports both voltages so either module will work OK. The only difference is that the 1.35v module draws less current if the system supports 1.35v..
Most users would like to match the second module to the existing one so we asked Sony again but have not received any sense at all!
Usually Sony factory fit the Samsung M471B5273CH0-CH9 4GB module but the datasheet for this RAM Module from Samsung says that this module comes in BOTH a 1.5v and a 1.35v version. It also says that the 1.35v version will work with 1.5v systems. Have a look at Page 6 of the datasheet here: -
http://html.alldatasheet.com/html-pdf/347916/SAMSUNG/M471B5273CH0/1824/6/M471B5273CH0.html
The first part of the Part Number is the same for both versions.
I am guessing that if the Part Number ends -CH9 then the module is 1.5v.
C = Standard Voltage
H9 = DDR3 - 1333
M471B5273CH0-CH9
If the Part Number ends -YH9 then the module is 1.35v
Y = Low VDD (1.35v)
H9 = DDR3 - 1333
M471B5273CH0-YH9
You can check your existing Part Number using Everest, Sandra or PC Wizard - or by taking the bottom off!!
If you can find out anything more, I'm sure several users will want to know.
