When the LCD first powers up it will turn on every pixel. When the computer boots it will send a reset command to the LCD drivers which turns off al pixels. If the LCD does this quick dark/light flash at power on you know the computer is starting to boot up.
Check what the LCD bias voltage is at the ribbon cable connector. Make sure it is getting there. I have had one machine with a break in that line. Given that you know the LCD works, if you have the correct bias voltage and all other signals it would follow that the computer it failing to boot all the way up. The most likely cause would be a bad RAM module in position zero. You can do the 'BEEP' test before pulling the RAM module out. Turn on computer, press B to start BASIC (I think, going off top of my head here) and then type BEEP and hit ENTER. If it beeps the computer is running but something is wrong with the signals to the LCD. Jeff Birt From: M100 <[email protected]> On Behalf Of Ken St. Cyr Sent: Tuesday, January 30, 2024 2:50 PM To: [email protected] Subject: [M100] LCD Troubleshooting Advice Hey folks - I'm working on an M100 and having some challenges with the LCD. Here are the symptoms: * No image at all on the LCD * Contrast dial does nothing * Beep test passes (boot > enter > beep > enter produces an audible tone), so it seems the system itself is working * The LCD works fine in a different M100 * VDD is reading +5v, and VEE is reading -5V * Checked the data pins on the LCD with my scope; they all look fine - looks like both data and addresses are making it to the LCD connector At this point, I'm baffled. Can anyone offer up some advice on what else to check? Thanks! //Ken S.
