Fixed a Viewsonic VP930B today

[PcarSBA]

The monitor wouldn't turn on, only the green power LED would come on and flash every 5 seconds. Interestingly, the monitor did get recognized by the laptop so though VESA so the logic must have been somehow working. The inverter wasn't turning on at all. No telling if the

The power supply put out 5.1 volts and 13.2 volts and the voltages looked reasonably good on the oscilloscope. On the logic board I found a good 1.8V and 3.3V at the two heat-sinked voltage regulators.

I went ahead and replaced three caps on the power supply board: A 2200uF (16V) and two 220uF (25V) caps since I had matching types on hand. Mind you the caps didn't show any swelling or signs of electrolyte leakage. After that the monitor fired right up.

What really stomps me is that the power supply voltages were very close to the spec values before replacing the caps and all looked well even with the oscilloscope. Also, the 220uF caps measured 216uF with the Fluke 123 scopemeter. I know this measurement is not equivalent to an ESR meter but still it leaves me wondering why the monitor didn't turn on before. Was it the 12V being too high and preventing the inverter to run?

Thoughts
Ingo

[PlainBill]

Re: Fixed a Viewsonic VP930B today

The caps had high ESR, resulting in high frequency (probably about 100 Khz) ripple on the outputs. The LDO regulators were unable to filter this adequately, causing erratic behavior of the signal card.

The 12V supply was slightly high because the inverter wasn't on. The 5V output of the power supply is regulated, the 12V is not.

PlainBill