[NTLK] MessagePad 100 (OMP H1000) Flickering/glitching

[NewtonTalk]

> On power-up the screen is garbled and glitches terribly with occasional
flickers of
> the newton logo and eventually sometimes showing calibration text/crosses
- 
> but mostly just random lines and black bars.? 
> Also no start-up chime.

Both are comparatively frequent defects of the OMP and MP100 models. As to
the missing startup sound: Usually it's not missing altogether. If you place
your ear right next to the speaker, most times you'll hear a weak excuse for
a startup sound. Provided you still have an excellent sense of hearing.
Which many of this list <flameShieldOn> might no longer have
</flameShieldOn>.

:-)

The cure, as you found out, is replacing C1. 

> One more surface-mount electrolytic not too far from the display ribbon
also
> with residue around it.? C51, valued 3.3uF @ 35V.? I had 3.3uF @ 50V on
hand
> (4mm dia, original was also 4mm.  I test-fitted a 5mm and it also fit, but
6.4mm
> cap did not allow the board to sit flat).? Clean and replace.?
Reassembled.
> And I have a beautiful working OMP now.? 

Wow. How cool! This is the type of information that usually makes my day.
Or, to be more precise, the days in at least the coming two weeks :-)

As luck will have it, I currently have two OMPs in the repair queue that
show the exact symptoms you're describing. And I think I have one more in
the shed that I put back years ago because I didn't have the time to figure
out a cure. These three animals have just advanced to the top of my repair
queue...

C51, by the way, is part of the LCD boosting circuit. The power to operate
the LCD is generated by a step-type chopper-system converter around IC 18.
In a nutshell, this converter generates 28 Volt from the battery voltage.
C51 is at the end of it. It is supposed to stabilize the LCD supply voltage.
I'd assume that the display would behave exactly the way you described if
this voltage isn't steady.

The interesting thing is that C1 and C59 are of the same type. Both are
cylindrical silver components with a rectangular black "housing" around
them. These two are the only capacitors of that type on the mainboard. So it
isn't surprising that they both failed, and it is reassuring there are no
other capacitors like this on the mainboard.

I know replacing C1 will always fix the sound issue, but until now I haven't
had a clue how to fix the display problem. This is why so far I haven't even
attempted to find a cure.

If replacing C51 will always fix this problem, you can proudly say that
you've done a lot towards keeping the Newton platform alive and kicking. And
you'll have saved not only your Newton, but many others all over the world,
starting with the three that are currently within my reach.

If anyone out there is reading this and contemplating fixing his OMP or
MP100: Please make double sure you use great care in anti-static-electricity
measures like a grounding band. There are field effect transistors in this
Newton model's power circuitry, and back at the time the OMP and MP100 were
developed, these transistors' resistance to static electricity often left a
lot to be desired. Back then I often thought it was sufficient to look at
such a transistor in an even slightly unfriendly way to make it give up the
ghost.

Thanks for sharing your findings!

Frank

-- Newton software and hardware at http://www.pda-soft.de