I recently picked up an as-is Apple Newton MessagePad on eBay. I mostly wanted it for the accessories: a pair of third-party game PC cards, a 9W AC adapter, and the original Apple Mac OS (Classic) and Windows 3.5-inch floppy disks.
When I got the Newton, I realized that it powered on, but there was no sound and the display was on but not displaying an image. As it turns out, this is a common problem with vintage Newtons and can be fixed with just a couple of new capacitors.
To fix the original Newton MessagePad (OMP), also known as the H1000, you need a PH00 Philips head screwdriver, a spudger, a soldering iron and a small amount of solder, 1x 100µF 16V capacitor, and 1x 3.3µF 50V capacitor. I used the capacitors from the OCR 24Value 500pcs Electrolytic Capacitor Assortment Box Kit I purchased from Amazon.
I don’t have any formal electronics training, so I relied on Colin’s This Does Not Compute video, Fixing a Common (and Inevitable) Apple Newton Problem as a general overview of the work that needed to be done. Once I had a basic idea of the repair job, I used EkriirkE’s Restoring/Repairing an Original Apple Newton MessagePad 100 (OMP H1000), start-to-finish video as a detailed repair guide.
I hope that if you come across a Newton OMP / H1000 in a similar condition as mine, that you can use this information and repair yours also.