Could be a bad contrast potentiometer. On Thu, Dec 28, 2023, 1:13 AM Eric <eric_1...@yahoo.com> wrote:
> Hi, > > I'm working to troubleshoot a non-functional Model 100 that only displays > pixels when powered up. Seems these computers occasionally have RAM issues > but I'm not sure how to identify faulty RAM that has not been removed. The > RAM modules are soldered in place and I would like to troubleshoot the > board to avoid unnecessary removal of parts. If anyone has other > troubleshooting steps, I'm happy to try them out. I have access to a logic > analyzer (Saleae software), oscilloscope, and DMM. > > Issue: When powered up, LCD shows pixels only (black screen w/adjustable > contrast) > > Troubleshooting Performed: > New NiCad installed and charged (memory switch on). Board traces > near battery corrosion have good continuity. > All capacitors were replaced. Board traces near leaking capacitors > have good continuity. > Cold Start and "BEEP" attempted. Beep was not heard. > DC/DC Converter Circuit meets specs per section V of Service Manual > 26-3801/3802 > Reset Signal meets specs per section V of Service Manual 26-3801/3802 > Logic Circuit meets specs per section V of Service Manual 26-3801/3802 > CPU, ROM, Ram all have activity on the scope. Clock signal looks > acceptable. > > Eric > >
