Laptop inverter board input voltage?

2

I am trying to repair a laptop where the back light has gone. I have tested the lamp by plugging it into another laptop inverter, the bulb lights up and is fine.

I have purchased a "tested" inverter board off of ebay but it did not fix the problem. I have tested the input pins for voltage. One of them reads 19 volts (pin 1 I think). Pin 2 in blank, pin 3 is 0.7 volts, pin 4 is 3.4v and pin 5 is 0v (presume this is negative).

Do these voltages seem right, in which case this would point to a faulty inverter wouldn't it?

The laptop is an Advent 7301.

SausageFingers

Posted 2011-05-08T22:21:17.530

Reputation: 177

Answers

1

From what I have read from researching this you typically have the following signals:

  • Vin - ~20V
  • Vcnt - 0V to 5V - low = disable, high = enable
  • A-dim - Analogue brightness control - anywhere between 0 and 3.3V - 0V is brightest, 3.3V is darkest
  • P-dim - Pulse Width Modulation brightness control - square wave between 0V and 1.6V
  • GND - 0V ground connection

A-dim and P-dim may be both there or only one there.

Looking at your voltages it could be that the Vcnt is in the low state disabling the inverter.

Majenko

Posted 2011-05-08T22:21:17.530

Reputation: 29 007

Thanks for replying - on the 5 pin on the connector I only have 4 wires, pin 2 is blank. Of the 5 you mention, which one am I likely missing? – SausageFingers – 2011-05-09T08:34:07.530

You probably have either A-dim or P-dim but not both. They both do the same thing but in different ways. I'd expect to see 20V(ish), 5V(ish) and somewhere between 0 and 3V on the 3 wires that give a reading. – Majenko – 2011-05-09T12:15:37.970

Thanks Matt, that makes sense. In which case I have the following: Vin=19V, Vcnt=0.7V, dim=3.4V. I'm assuming that due to the low voltage (0.7V) on my Vcnt that this is causing the inverter to fail, does this sound logical? I'm told that this model has a common problem with a voltage regulator chip. Could this be related? – SausageFingers – 2011-05-10T11:54:47.450

Vcnt at 0.7V will be telling the inverter to switch off. As for your voltage regulator chip - I really can't say. – Majenko – 2011-05-10T18:13:01.763

Hypothetically speaking, if I were to bridge the dim 3.4V to the Vcnt 0.7V, would that be enough voltage to enable the inverter? Or am I likely to blow the mobo? – SausageFingers – 2011-05-12T10:10:59.390

No idea. If it's A-dim then it might work, as Vcbt is just a TTL level signal. If it's P-dim then who knows what would happen if yuo apply a square wave to Vcnt...? – Majenko – 2011-05-12T15:35:10.863

Asked: 2011-05-08T22:21:17.530

Viewed: 14 917 times

Active: 2019-12-20T20:26:56.517