Tech: Asteroids monitor of death

[karlcdoe]

Hmm,

Well, I  finally got round to pulling my monitor apart to investigate the magic smoke. It appears I have an electrohome G05801 and the resistor at R906 on the HV board is toast -though the monitor was actually still working when I turned it off I expect the resisitor was only half way through cooking.

I notice in the monitor manual/FAQ it says this is a  'safety resistor designed to prevent damage to Q903 should the output circitry come under excessive current drain' but then describes it in more mundane terms as 1 Ohm, 1/2 watt +- 5% so I am assuming there is nothing special about this resistor?

I was thinking along the lines of replacing it, powering up and seeing if I get a firework display but then I don't want to wreck the HV tranformer. So assuming it hasn't gone bad due to age (looks like the original 1980 component....) what exactly would cause excessive current drain? Is this indicative of another duff component on the HV cage or can it be caused by crazy deflection inputs, shoddy PSU regulator.

Incidentaly,  I recently noticed what might be considered blooming although this was clearly *only* in the Y axis and gets better when the monitor warms
up and not
worse...

Any advice welcome....

Thanks in advance.

Karl.

 

[P-Man]

Quoting Karl Doe <karlcdoe@yahoo.co.uk>:

> I notice in the monitor manual/FAQ it says this is a  'safety
> resistor designed to prevent damage to Q903 should the output
> circitry come under excessive current drain' but then describes it
> in more mundane terms as 1 Ohm, 1/2 watt +- 5% so I am assuming
> there is nothing special about this resistor?

Replace it with like-for-like or a higher wattage if you like.. see if
the burning continues, but quite often, this is fairly normal..

> I was thinking along the lines of replacing it, powering up and
> seeing if I get a firework display but then I don't want to wreck
> the HV tranformer. So assuming it hasn't gone bad due to age (looks
> like the original 1980 component....) what exactly would cause
> excessive current drain? Is this indicative of another duff
> component on the HV cage or can it be caused by crazy deflection
> inputs, shoddy PSU regulator.
>
> Incidentaly,  I recently noticed what might be considered blooming
> although this was clearly *only* in the Y axis and gets better when
> the monitor warms
> up and not
> worse...

This could well be a dodgy Y size or linearity pot, twirgle the pots
on the deflection board back and forth, putting them back in their
original position when yo uare done, do the same for the pots on the
game pcb itself. See if that makes any difference.

> Any advice welcome....
>
> Thanks in advance.
>
> Karl.

I can't actually get to my monitor manuals drawer at the moment to
help with the resistor shenanigans.. Despite that drawer being the TOP
drawer of the second filing cabinet, shows you how much stuff is piled
up in front of it

enjoy.
__________________________________________________________
Andrew Welburn - http://www.andys-arcade.com/
WANTED - Deith Virtua Fighter sideart(RHS), Berzerk Control panel
Working Atari Xevious PCB | Long STERN fire buttons (Berzerk)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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[karlcdoe]

Hi Andy,

Thanks for the info. BTW: are you implying it's normal for the burning to
continue or that it's normal for this resistor to fail

Cheers

Karl