Pin 17 is high? Ie /Reset? On Tuesday, January 30, 2024, Ken St. Cyr <[email protected]> wrote:
> 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 <[email protected]> on behalf of Stephen > Adolph <[email protected]> > *Sent:* Tuesday, January 30, 2024 9:30 PM > *To:* [email protected] <[email protected]> > *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 <[email protected]> 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 <[email protected]> on behalf of > [email protected] <[email protected]> > *Sent:* Tuesday, January 30, 2024 6:20 PM > *To:* [email protected] <[email protected]> > *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 <[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. > >
