• Please review our updated Terms and Rules here

Toshiba T1800 LCD problem

Yes, that issue is indicative of no signal being sent to the actual pixels in the screen. This could mean that the LCD driver board has an issue, the computer isn’t starting a proper display output, or it’s missing a voltage that it needs.
I discovered after a number of tests that the LCD occasionally displays normal but unstable.
Adjusting the contrast then functions as intended.
WechatIMG743.jpegWechatIMG749.jpeg

The characters can still be viewed from the top viewpoint even when the screen is abnormal, but they are very obscure.
At that time, adjustment for contrast is still working but it can't make the screen dark enough to make the characters visible.
All of these show that the signal was correctly sent to the LCD panel from the mainboard.
As you point out, i think the LCD power supply circuit or the contrast adjustment circuit may be at fault.


The maximum voltage to the screen is only 5V(the thick black wire is regarded as the power supply's negative terminal.), though I'm not sure if I measured the right line.
WechatIMG744.jpeg

Every component on the LCD panel seems to be no problem.
WechatIMG745.jpegWechatIMG746.jpegWechatIMG747.jpegWechatIMG748.jpeg
 
Last edited:
That screen looks similar to an early Powerbook screen. Check to see if you have high voltage to the screen, I believe it's either 12, 25 or 50 volts. If that voltage source is missing, the screen won't work. IIRC, the voltage is present on the ribbon cable going to the screen.
The maximum voltage to the screen is only 5V(the thick black wire is regarded as the power supply's negative terminal.), though I'm not sure if I measured the right line.
Is 5V normal ?
 

Attachments

  • WechatIMG744.jpeg
    WechatIMG744.jpeg
    132.2 KB · Views: 3
Seems like a signaling problem them? Maybe the computer is only posting intermittently? Check the inverter board where the contrast control is for any caps as well.
 
Last edited:
The maximum voltage to the screen is only 5V(the thick black wire is regarded as the power supply's negative terminal.), though I'm not sure if I measured the right line.
Is 5V normal ?

I can't be 100% sure yours is the same, it just looks similar to a PB 100 screen.

There's one wire going into the screen that's high voltage used for biasing or something. If that voltage is missing, the screen won't work.
 
not the same model of LCD, but similar. Both are made by sharp. I agree with whoever said earlier - looks like something in the circuit responsible for contrasts control.
 
I measured the PSU's voltage.
Every pin's voltage was recorded.
DSPV is the name of 3 pins (14.9v). Does it stand for "Display voltage" as an acronym?
Nevertheless, 14.9V shouldn't be present.
According to the maintenance manual, it ought to be 5V.
The manual states that PSU only outputs +5V, +4.7V, +12V, and -9V.
Right?

Next, I'll inspect routing & wiring to the LCD.
0230316142142.jpg
 
Last edited:
Back
Top