[Coco] Re: Help using the Coco3 with a 1084S-D2 Monitor

[Gene Heskett]

On Wednesday 12 November 2003 13:42, Hank wrote:
>Torsten,
>
>
>
>I have a NTSC Coco3 with the newer Gime Chip.
>
>Can I make internal Adjustmets inside the 1084S-D2 Monitor?
>
>Hank

Be extremely carefull in there Hank, there are voltages in there that 
can not only give you nasty burns, but can kill.  High voltage at the 
side of the crt is around 27 kilovolts.  Thats not normaly lethal 
unless applied directly across the chest area because its current 
limited to around a milliamp or so, but it can darned sure get your 
attention in a manner you'll remember the rest of your life.

WRT the synch problem, I'd expect you'll have to do there what many of 
us did for the maggy monitors, which are very similar, and which 
commie did right inside the molded plug of their special amiga 
cables.  Hidden away inside that plastic db23's molding is a cmos 
(thats why its so easily damaged, an lsttl works just as well, I've 
done that) to buffer the sync signals and bring them up to about 4 
volts.  I suspect you may have to do a similar operation for the 
coco.  It was done on the amiga's because the agnus chip had 
overcurrent sensors in it that shut it down if it tried to drive too 
many 75 ohm loads.  It could drive the rgb lines ok, but add a 75 ohm 
load on the synch lines and it shut itself down.  That monitor has 75  
ohm terminations on every signal line going into it, and I don't 
think the gime is up to hitting a low ohms load like that with enough 
voltage to make the monitor see it.  And its probably warming up the 
gime trying, which isn't good for a chip thats almost made out of 
unobtainium today.

Any old NAND gate, used 2 in series so the polarity isn't changed, 
should do it just fine.

On the box box amiga's, tehre was a 5 volt powered pin to supply that 
chip, but I don't recall if the coco3 can be rigged to do that or 
not.

>PS: are far as the NEC-3Ds goes, I found those RBG Gounds on pinds
> 6,7, and 8 do not need to be connected when hooking it up to the
> Coco3.  It works great just using any of the ground pins.
>
>----- Original Message -----
From: "Torsten Dittel" <Torsten at Dittel.info>
>To: <coco at maltedmedia.com>
>Sent: Wednesday, November 12, 2003 6:13 AM
>Subject: [Coco] Re: Help using the Coco3 with a 1084S-D2 Monitor
>
>> Hi Hank,
>>
>> > You guys have any ideas on this one?
>>
>> I checked your pin out on all 3 components and it looks OK (just
>> to complete it, pins 6,7,8 on the NEC 3D are the GND lines for
>> R,G,B).
>>
>> I noticed "glitches" in vertical sync on my 1084S-P1 (AFAIR the
>> only difference between the P1 and the D2 is a head phone jack)
>> too. The funny thing is that it's only with one of my two (PAL)
>> CoCo3s. Both work fine with the NEC 3D. One of the CoCo's is
>> US-made, the other Korean. The difference is, that the (newer) US
>> model has a new version of the GIME chip and I guess this is
>> causing the problems because of slightly different signal timing
>> and/or amplitudes. I never cross-changed the GIME chips nor
>> checked it out with an oscilloscope.
>>
>> Hope this helps.
>>
>> Regards,
>> Torsten from Germany
>>
>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> http://five.pairlist.net/mailman/listinfo/coco

-- 
Cheers, Gene
AMD K6-III at 500mhz 320M
Athlon1600XP at 1400mhz  512M
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