[NTLK] The weirdest MP130 defect I've ever had

From: Frank Gruendel (fg2_at_pda-soft.de)
Date: Tue Oct 14 2003 - 15:57:28 PDT


Hi folks,

here's something I've never had in all the time I've been
fixing Newtons...

Last week I got a Newton 130 on my workbench whose backlight
wasn't working, otherwise the machine was perfectly ok.

I checked the backlight with my backlight tester, it
worked just fine.

So, thought I, another of the R112's has bitten the dust
(see http://www.pda-soft.de/mp130fixes.html). I replaced
all 5 resistors, re-soldered U43 (which had more or less
left the mainboard, it was a miracle that the 130 still
powered on) and was very confident that everything would be
wonderful after reassembly.

Just in case, I checked the backlight again with my backlight
tester, it was working just perfect. Then I put the
main logic board back in.

No backlight...

Well, these things happen. Maybe something else in the
backlight driver circuit had given up the ghost. I ripped
the mainboard out again and installed another one.

No backlight...

Well, these things happen. Although fairly unlikely, it is
not impossible that two main logic boards have exactly the
same defect. So I ripped the second one out and put in a
third one.

No backlight...

Contemplating whether society wouldn't be better off if I
spent the rest of my life in a mental asylum, I checked the
backlight again with my backlight tester. It was perfectly ok.

Being very much aware that putting in yet another main logic
board would be the very opposite of professionalism,
I put in yet another main logic board.

No backlight...

I then unsoldered the backlight of the built-in display and
soldered that of a second display to the main logic board.
Of course, I tested the second display's backlight with my
tester. It was perfectly... (I think you get the picture).
I switched the Newton on.

No backlight...

Being very much out of ideas, I soldered the backlight of the
built-in display back on. I then unplugged the cable of the LCD
itself and plugged that of the other display that was still lying
next to the Newton in.

Trara...

I was able to switch the backlight (of the built-in display)
on and off while displaying the screen on the other display.

Hmmm...

Obviously this Newton's display unit has a defect that
prevents that the mainboard (any mainboard) drives the
backlight while the LCD is used. The LCD itself
is fine. So is the backlight, as my tester shows.
Having no idea whatsoever how this can happen, I took
a LCD / backlight combo from my spare parts pool and married
it to the (excellent) touchscreen of the original display.
I switched the Newton on.

I HAD BACKLIGHT! YEAH!!

but...

...since when is the backlight active when the Newton is
switched on? Switched on by a definitely short pull at the
power switch?? Every time I switched the Newton on, the
backlight was on, too.

With the mental asylum becoming a more and more promising option,
I had a look at the installed packages.

AHAAAA...

There's Backlight Plus! Which is capable
of switching the backlight on automatically at power up. It
claimed, though, that its current setting was NOT to do this.

Thinking that it might not be such a bad idea after all to
submit Newton packages to mental asylums, too, I did a hard reset.

Since then the Newton behaves the way every Newton should
behave in the first place.

Oh boy. If only I wasn't that stubborn. Maybe I'd even get
some sleep time and again.

Frank

-- Newton Software and Hardware at http://www.pda-soft.de

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