[NTLK] MessagePad 100 (OMP H1000) Flickering/glitching screen, no/low sound fix

Erik Johnson apple.newton at retro.network
Fri Oct 5 12:40:33 EDT 2018

I recently purchased a defective Original MessagePad for a good price 
hoping to fix it blindly.  And I did; 2 compact electrolytic capacitors 
inside had leaked and gone bad, there are 3 in total inside the device 
but 1 is not the typical compact/surface-mount kind that goes bad and 
can probably be ignored safely for now (My LCR meter showed it well 
within spec).
Symptoms?  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.

When first removing the back cover C1 had a white fog around it, it's a 
surface mount and is located right next to the speaker wires.  Original 
value is 100uF @ 4V.  I only had 100uF @ 25V on hand with a slightly 
larger 6.4mm diameter body and it fit fine. After cleaning the residue 
off with isopropyl alcohol and replacing it I got sound - a start-up 
chime!  But the video was still broken.  In my LCR meter C1 still 
measured 100u but with very high ESR (almost 1K)

All the other capacitors visible are tantalum solid-state caps and 
should be fine.  Plus the one obvious through-hole cap that isn't the 
compact type to go bad, typically.

So I removed the logic board to have a look at the other side; and lo!  
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.  Useless 
handwriting --recognition-- mutilator and all.  C51 did not register on 
my LCR meter at all, completely bust.

Pictures here https://imgur.com/a/69J7YWl

- Erik

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