How do you test a backlight ? IBM a31p

From	mike <spamme9@gmail.com>
Newsgroups	comp.sys.laptops
Subject	How do you test a backlight ? IBM a31p
Date	2012-08-29 17:01 -0700
Organization	A noiseless patient Spider
Message-ID	<k1maic$th0$1@dont-email.me> (permalink)

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I've got a Thinkpad a31p with no backlight.

I put another backlight on the inverter and got no light.
I tried the Thinkpad backlight on another inverter and got no light.
Initial guess is both bad.
Is there any reason the Thinkpad light should be different from any other?
I put a 1M resistor in series with a DC power supply.
A Toshiba backlight fires at about 1500V and stays lit
back down to 1000V or so.

The Thinkpad light starts drawing current at about 1500V
but doesn't light.  I'm trying to think of a failure mode
that would cause this behavior.  If the bulb is cracked,
wouldn't is just be an open circuit at any rational voltage?

Is there a source for schematics or reference inverter designs?
IBM put LED indicators on the inverter board, so you can't just
cobble in another.  They're rare and more expensive than buying
a whole used A31p.
It's got the 1600x1200 display, so it's worth some effort to try
to fix it.

According to the service manual. There are several ways to turn
off the display, but I'm assuming that if there's data on the display,
the backlight should always be on???

The service manual mentions that fuses aren't covered under warranty,
but there's no mention of a fuse anywhere.
I once had a thinkpad with a bad display fuse.  Haven't taken it
that far apart yet.

Suggestions?
Thanks, mike

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Thread

How do you test a backlight ? IBM a31p mike <spamme9@gmail.com> - 2012-08-29 17:01 -0700
  Re: How do you test a backlight ? IBM a31p BillW50 <BillW50@aol.kom> - 2012-08-29 20:12 -0500
    Re: How do you test a backlight ? IBM a31p mike <spamme9@gmail.com> - 2012-08-29 19:15 -0700
      Re: How do you test a backlight ? IBM a31p "BillW50" <BillW50@aol.kom> - 2012-08-30 05:42 -0500
        Re: How do you test a backlight ? IBM a31p mike <spamme9@gmail.com> - 2012-08-30 05:55 -0700
          Re: How do you test a backlight ? IBM a31p BillW50 <BillW50@aol.kom> - 2012-08-30 10:25 -0500
            Re: How do you test a backlight ? IBM a31p mike <spamme9@gmail.com> - 2012-08-30 08:33 -0700
              Re: How do you test a backlight ? IBM a31p BillW50 <BillW50@aol.kom> - 2012-08-30 11:08 -0500
                Re: How do you test a backlight ? IBM a31p BillW50 <BillW50@aol.kom> - 2012-08-30 11:33 -0500
                Re: How do you test a backlight ? IBM a31p mike <spamme9@gmail.com> - 2012-08-30 10:43 -0700
                Re: How do you test a backlight ? IBM a31p BillW50 <BillW50@aol.kom> - 2012-08-30 17:19 -0500
                Re: How do you test a backlight ? IBM a31p mike <spamme9@gmail.com> - 2012-08-30 10:37 -0700
                Re: How do you test a backlight ? IBM a31p BillW50 <BillW50@aol.kom> - 2012-08-30 17:06 -0500
                Re: How do you test a backlight ? IBM a31p wrat@panix.com (the wharf rat) - 2012-09-01 06:33 +0000
                Re: How do you test a backlight ? IBM a31p BillW50 <BillW50@aol.kom> - 2012-09-01 12:36 -0500

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