Sony Vaio Power Supply Problem

November 12, 2008

This is an overview of the power-supply issues I have had with my Sony Vaio notebook computer. I have owned two Sony notebook computers in the past, and despite the problem I am about to describe to you, I will probably continue to stick with the Sony Vaio line of notebooks in the future. The performance of this notebook in particular is exceptional. It is a Sony Vaio VGN-CR320 E/N, which I purchased in the beginning of 2008.

This past weekend, I noticed a tingling on my wrists as I was writing some code. The sensation was coming from the metallic trim piece along the bottom edge of the notebook, just below the keyboard. I decided to take a look at the voltage on this metal trim piece using an oscilloscope:

voltage_on_notebook

I was very surprised to see there was 150 VAC (p-p) there! So, I thought, if there was 150 VAC on the metal trim, then the USB grounding shield must also be at 150 VAC... Sure enough, it was!

voltage_on_usb_shield voltage_on_notebook_scope

Then I remembered my notebook was plugged in to the AC adapter, supplying 19.5 VDC to the notebook. So, I disconnected the AC power adapter, and took the measurement while running on battery:

voltage_on_notebook_on_battery

Almost 20 VAC (p-p), running on battery! Even if I inhibit the LCD display by pushing the 'display off' button on my notebook, this 20 VAC is still present (I was thinking the CCFL inverter was the culprit). As a workaround, I plugged a grounded USB cable into the notebook. This did the trick, as the AC voltage on the metallic trim and on the USB shields disappeared. The black USB cable in the photo below is connected to ground.

solution_with_grounded_usb_cable

It turns out, this is a very common problem with Sony Vaio notebook computers. The main complaint is a tingling sensation on the palm rest, but I think that if these people measured the voltage on their USB shields, they might see 150 VAC also. I wonder how many USB peripherals have been adversely affected by this?

I called Sony tech support, and they are familiar with the problem. They are offering a free 'three prong' AC adapter that should fix the issue. However, I don't see how this will emilinate the 20 VAC that exists when the notebook is running off battery...

cole <@> coledd.com

electronic design consultant ohio embedded linux arm cortex m0 m3 pic msp430 stm32 nxp lpc1111 lpc1114 microcontroller analog instrumentation embedded software development firmware engineering pcb layout implantable medical device mics band telemetry inductive power coupling IEEE 1588 ptp rfid electromagnetic wireless radio