Yes, I probed the LCD signals with my scope, and didn't notice anything out of the ordinary. I suppose I could hook up a logic analyzer to the LCD data pins and see if anything is getting garbled...
//Ken S ________________________________ From: M100 <m100-boun...@lists.bitchin100.com> on behalf of Stephen Adolph <twospru...@gmail.com> Sent: Tuesday, January 30, 2024 9:30 PM To: m...@bitchin100.com <m...@bitchin100.com> Subject: Re: [M100] LCD Troubleshooting Advice Ken do you have a scope? We are looking for a fault that kills the lcd and drives the current up. I would probe the signals and see if there is a clue there. ..steve On Tuesday, January 30, 2024, Ken St. Cyr <k...@stcyrfamily.net<mailto:k...@stcyrfamily.net>> wrote: The beep test does work, so I know the machine is operating. I checked all the LCD signals again, and they all look normal. I also checked the pot, and the voltage was a little high compared to a working unit (+/- 3v on the broken one ... the working unit was around +/- 2.6v). One thing that I did notice is that when I run it from my power supply, it's drawing 80mA (LCD disconnected), whereas the working one is only drawing like 50-something mA. Makes me wonder if there's another short somewhere (I already found and repaired one on this unit). But since the system seems to be running basic code, I'm wondering if the short is on one of the LCD data lines. I looked pretty closely with my microscope for quite a while and didn't find anything, and my meter isn't showing a short anywhere, either 😕 I appreciate the pointers so far... Any other thoughts? //Ken S ________________________________ From: M100 <m100-boun...@lists.bitchin100.com<mailto:m100-boun...@lists.bitchin100.com>> on behalf of bir...@soigeneris.com<mailto:bir...@soigeneris.com> <bir...@soigeneris.com<mailto:bir...@soigeneris.com>> Sent: Tuesday, January 30, 2024 6:20 PM To: m...@bitchin100.com<mailto:m...@bitchin100.com> <m...@bitchin100.com<mailto:m...@bitchin100.com>> Subject: Re: [M100] LCD Troubleshooting Advice 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 <m100-boun...@lists.bitchin100.com<mailto:m100-boun...@lists.bitchin100.com>> On Behalf Of Ken St. Cyr Sent: Tuesday, January 30, 2024 2:50 PM To: m...@bitchin100.com<mailto:m...@bitchin100.com> 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.
