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