Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

HP LT1940-screen fades out (shuts off)

Status
Not open for further replies.

fezder

Well-Known Member
Ok, i got yet another hardware to repair, or at least attempt.
well actually two, other monitor i'm repairing has flikcering screen, only backlight flickers, nothing else shows up. i opened it and found some wasted electrolytics. so far, no big problems with that one....but This HP model, is bit another story:
It seems to power-up somehow, but after short period, couple seconds, screen turns off by itself.
i checked caps, no pulgs or other mechanical damage, checked them with esr meter, seems ok results. There is strange noise at startup, coming from one of transformers, i dont think its mains hum, sounds bit higher freguency. And when i turn screen on, backlight comes alive for some time, makes bit of noise like arcing or something, hard to describe. Is there other common faults with monitors than bad caps, and what i should check now?. i can take photos and service manual IS available in hand.

thanks for any help
 
Typical problems are the tubes, the inverter transformers, small blue HV capacitors, or poor connections.

If you google the datasheet for the inverter chips you may be able to figure out how to disable the auto-shutdown that prevents you working on it.
 
Thanks for reply, are those blue hv caps ceramic ones, like others found in SMPS systems? and is there any downside for disabling auto-off, like making more damage, as there is something that initiates the shut-off, right?. i try to google those chips, maybe it helps, as you suggested :).
 
hmm, i wonder did i mis-informed about situtaion: only screen shuts off, first it just dims, then fades completely, otherwise monitor stays on, power led doesn't turn to orange, it stays green
 
hey, little progress in this matter, i made some measurements with 'scope, from 1200AP40:s pin 5 (drive output) to see if if chip is faulty, seems not, but what do you think? sorry about image quality....scope settings are as follows:
10v/div, with 10x scope attenuation.
5ms/div horizontal
none change seen when fault occurs.

ref. point for scope was chassis of monitor, dont know was it the best place, but reliable.
i can take another shot if necessary
 

Attachments

  • output.jpg
    output.jpg
    30.2 KB · Views: 266
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top