3 Replies Latest reply: Mar 23, 2011 9:20 AM by bebo_
bebo_ Level 1 Level 1 (0 points)
Hello,
I have an iMac g3 which always had worked without any big problems.
Last time when i used it, it was turned on, I went away for a very short time and when I came back it was turned of. Pushing the front power button doesn't make any sense.

I took it apart for measuring the voltages at the logic board. this are the results:
5V trickle: 4.98V
DCO voltage: I couldn't measure it(the location of C10 is moved in my model)
voltages at the down converter(after I pressed the power button):
12V:+/- 11V
5V: 4->4,5V
3.3V: 2V

Also a green led on the logic board is lit after the power button is pressed but it doesn't light stable(not lit bright, flashes at a reasonable frequency), the The hard drive makes a little noise from trying to spin up.
Also I hear the transformers making their normal (high frequency) noises.
Before this problem stared,the machine booted one time with no video.
Another time it booted with a wavy/out of focus image.

Does anyone know what's wrong whit, probably the PAV? Should it be a capacitor or the FBT?

Already thanks for helping me,
Bert

iMac G3 Snow 600MHz, Mac OS X (10.4.11), 512MB Ram-40GB HD-AirPort
  • littleshoulders Level 6 Level 6 (9,525 points)
    Hello Bert,

    First of all, Welcome to the  Discussion forums!

    Do you know that the iMac's pram battery is good? Might need replacing.

    littleshoulders
  • bebo_ Level 1 Level 1 (0 points)
    Yes, I've already checked the battery, it was still at the required voltage,I've also resetted the PRAM, no results.
    The Down converter is okay I think, I've replaced the down converter from another broken iMac(a slower one I think a 400MHz) and it gives the same results.

    Bert
  • bebo_ Level 1 Level 1 (0 points)
    I've took the machine apart and also removed the crt.
    Now I was measuring some components and i noticed that the Horizontal Deflection Output transistor(HOT) is shorted between every contact of the transistor.

    I would try to replace it, but the question is why has it blown?
    A bad HV capacitor or a bad driver transformer?(a small transformer which is located left from the crt's neck when you're standing in the front of the machine.)
    Or should it something else that caused the problem?
    ( http://www.repairfaq.org/samnew/tvfaq/tvhorkboeh.htm )

    Bert