help with PowerBook 100 LCD signals?

[asentientbot]

Hi again, I have some more questions about the PowerBook 100 from this thread.

We weren't able to properly fix the missing LCD_VEE, but my friend got an isolated bench PSU for another project, and we realized she could temporarily create LCD_VEE with it to test further. She removed Q12 (page 11 of the schematic) for safety and injected -22 V at TP055. There are noticeable improvements with that present: contrast control works now, and the display shows lines when resetting. However, there is still no image.

Are we correct that this points to a second unrelated display issue?

We checked the +5 V and GND pins on J12 (page 2) which are as expected, but we don't know enough to check the other signals from U8/VIDEO (page 5) and U22/M50753 (page 8).

Does anyone know what we can do to narrow it down?

Thank you!

 

[demik]

Hi again, I have some more questions about the PowerBook 100 from this thread.

Are we correct that this points to a second unrelated display issue?

We checked the +5 V and GND pins on J12 (page 2) which are as expected, but we don't know enough to check the other signals from U8/VIDEO (page 5) and U22/M50753 (page 8).

Does anyone know what we can do to narrow it down?

Thank you!

No idea where the issues lies, but you I can help you check the basic signals

Check "clock" signal continuity like this (page 5)
- CL1 should be in the kHz range, probably around 12 kHz ( short pulses, may be off by a factor or 2-4 depending on LCD model )
- CL2 should be around 1.9 MHz ( about 40-50% duty cycle )
- FLM should be very short pulses at a little more than 60 Hz

As for LD0-3+UD0-3, _if_ the Mac had booted and is stuck in the grid screen before booting (the one with the floppy icon), you should see clock-like signals there with occasional gibberish. Otherwise it's just noise. Theses are not read if the three clock signals aren't above aren't working.

 

[ObeyDaleks]

I didn't read the whole previous thread, but did you actually check if the machine itself is ok? Simplest way would be to use a boot floppy and listen for the standard floppy activity.