iMac without monitor ?

News schrieb:
> "Johan Coppieters" <johan.DeleteThis@duo.be> schreef in bericht
> news:3f462d16$0$240$4d4efb8e@read.news.be.uu.net...
>
>>Hello,
>>
>>I'm having an iMac with an external VGA connector.
>>The video hardware broke down and the monitor is only showing blue and
>>white. I've hooked up an external monitor and the machine works great
>>like this.
>>
>>So I removed everything from the original platic casing. And I'm trying
>> to only keep the motherboard, so that I can put it in a smaller box
>>which fits under the external monitor.
>>
>>However the iMac won't boot, without EVERYTHING attached. Anyone got an
>>idea how I can get rid of the video hardware? The external VGA connector
>>is attached to the motherboard. The motherboard has its own power
>>supply, so theoretically it should be possible...
>>
>>Any help is welcome.
>>Johan Coppieters, Brugge, Belgium.
>>
>
>
> sorry, wrong theory !
> maybe it's only a bad RGB video cable between the deflection board and the
> crt neck board.
>
>
>
This sounds as if you've got a similar machine to mine: iMac DV 400 as
of approx end 99 / start 2000.
I'm currently searching for a cause in instabilility in power supply and
figured out, that the power runs like this:

First step is a primary switching power supply, which does a couple of
different voltages for flyback transformer, tube heating, deflection
unit, video amp and deflection setup stuff. Also it does source 127 V to
the power supply for the logic board. Funny thing: that power (127 V)
goes from these small connectors from the analog board together with the
power for the video amp to the video pcb on the cathode and from there
back to the digital board through the metal connector which carries the
video signal. The 127 V runs over half of the digital board to finaly
enter the power supply.

So if you just removed the connectors to the video pcb, then you've cut
of the power line. Anyway - showing 'only blue and white' is nearly
impossilbe. You should check which color is missing. Maybe it's only the
video stage on the video board - this transistor can easily be replaced.

Gerd.

News wrote:
> "Johan Coppieters" <johan.RemoveThis@duo.be> schreef in bericht
> news:3f462d16$0$240$4d4efb8e@read.news.be.uu.net...
>
>>Hello,
>>
>>I'm having an iMac with an external VGA connector.
>>The video hardware broke down and the monitor is only showing blue and
>>white. I've hooked up an external monitor and the machine works great
>>like this.

>
>
> sorry, wrong theory !
> maybe it's only a bad RGB video cable between the deflection board and the
> crt neck board.
>
>
>

The Mac went to an Apple repair store
and their answer was:
we need to replace the video board...
So yes, my theorie is based on they being right.

Johan.
>

Gerd,

we're definitly going into the right direction with this one,
(I noticed the small connector and measured 128 volts on mine too, but I
couldn't figure out from where the 128 volt was comming)

so a big win for my project would be:
How can I reroute the 127 volt
without going over the pcb on the cathode,
this would make the iMac-with-no-screen a lot smaller.

Also any idea on other parts which can be powered down
on the video board, so I can reduce power consumption
(and heat)


Thanks you VERY much,

Johan.


>>
>>
> This sounds as if you've got a similar machine to mine: iMac DV 400 as
> of approx end 99 / start 2000.
> I'm currently searching for a cause in instabilility in power supply and
> figured out, that the power runs like this:
>
> First step is a primary switching power supply, which does a couple of
> different voltages for flyback transformer, tube heating, deflection
> unit, video amp and deflection setup stuff. Also it does source 127 V to
> the power supply for the logic board. Funny thing: that power (127 V)
> goes from these small connectors from the analog board together with the
> power for the video amp to the video pcb on the cathode and from there
> back to the digital board through the metal connector which carries the
> video signal. The 127 V runs over half of the digital board to finaly
> enter the power supply.
>
> So if you just removed the connectors to the video pcb, then you've cut
> of the power line. Anyway - showing 'only blue and white' is nearly
> impossilbe. You should check which color is missing. Maybe it's only the
> video stage on the video board - this transistor can easily be replaced.
>
> Gerd.
>

Gerd,

we're definitly going into the right direction with this one,
(I noticed the small connector and measured 128 volts on mine too, but I
couldn't figure out from where the 128 volt was comming)

so a big win for my project would be:
How can I reroute the 127 volt
without going over the pcb on the cathode,
this would make the iMac-with-no-screen a lot smaller.

Also any idea on other parts which can be powered down
on the video board, so I can reduce power consumption
(and heat)

And yes, the "only blue and white" is inaccurate,
but the apple repair store wanted to replace
the video pcb, so I gave up on it.


Thanks you VERY much,

Johan.



>>
>>
> This sounds as if you've got a similar machine to mine: iMac DV 400 as
> of approx end 99 / start 2000.
> I'm currently searching for a cause in instabilility in power supply and
> figured out, that the power runs like this:
>
> First step is a primary switching power supply, which does a couple of
> different voltages for flyback transformer, tube heating, deflection
> unit, video amp and deflection setup stuff. Also it does source 127 V to
> the power supply for the logic board. Funny thing: that power (127 V)
> goes from these small connectors from the analog board together with the
> power for the video amp to the video pcb on the cathode and from there
> back to the digital board through the metal connector which carries the
> video signal. The 127 V runs over half of the digital board to finaly
> enter the power supply.
>
> So if you just removed the connectors to the video pcb, then you've cut
> of the power line. Anyway - showing 'only blue and white' is nearly
> impossilbe. You should check which color is missing. Maybe it's only the
> video stage on the video board - this transistor can easily be replaced.
>
> Gerd.
>

"Johan Coppieters" <johan RemoveThis @duo.be> schreef in bericht
news:3f49d58b$0$253$4d4efb8e@read.news.be.uu.net...
> News wrote:
> > "Johan Coppieters" <johan RemoveThis @duo.be> schreef in bericht
> > news:3f462d16$0$240$4d4efb8e@read.news.be.uu.net...
> >
> >>Hello,
> >>
> >>I'm having an iMac with an external VGA connector.
> >>The video hardware broke down and the monitor is only showing blue and
> >>white. I've hooked up an external monitor and the machine works great
> >>like this.
>
> >
> >
> > sorry, wrong theory !
> > maybe it's only a bad RGB video cable between the deflection board and
the
> > crt neck board.
> >
> >
> >
>
> The Mac went to an Apple repair store
> and their answer was:
> we need to replace the video board...
> So yes, my theorie is based on they being right.
>
> Johan.
> >
>

sorry, i am a technical engineer around 50km from Bruges and i was wondering
how it can be possible you can see white if you don't see any red nor green
???

repair stores don't repair boards, they only replace them.
the video cable is connected between the analog board (that's the one with
the FBT on it) and the crt neckboard (on the picture tube).
both board are one assembly (the video board can have p/n: 661-2212).
it's correct if you replace it, the iMac will work again as it should be.