[Coco] CoCo 3 to RBG...

[gene heskett]

On Wednesday, July 20, 2011 06:39:24 PM Steven Hirsch did opine:

> On Wed, 20 Jul 2011, gene heskett wrote:
> > On Wednesday, July 20, 2011 04:52:43 PM Steven Hirsch did opine:
> >> On Wed, 20 Jul 2011, gene heskett wrote:
> >>> On Wednesday, July 20, 2011 01:00:14 PM Steve Batson did opine:
> >>>> Steve,
> >>>> 
> >>>> Can you provide details on building your 2 chip circuit to get it
> >>>> working?
> >>>> 
> >>>> I received mine this week, built cables to Map Coco 3 RGB signals
> >>>> to the on board 8 pin connector as they describe. The board
> >>>> powered fine, I can access it's menu and functions, but no Coco
> >>>> output. Just a green screen, but I don't think it's Coco output
> >>>> though. Coco works fine with composite  out to TV.
> >>>> 
> >>>> Any help will be appreciated!  :)
> >>> 
> >>> This is going to be best troubleshot with a decent scope, only that
> >>> can give you a definitive answer.
> >>> 
> >>> Oh Wait, you said the 8 pin connector?  Humm, I may be half a bubble
> >>> off here, but ISTR reading in the excruciatingly fine print (I had
> >>> to drag out an old projector lens & use it for a magnifying glass
> >>> to read that teeny little booklet) that the 8 pin connector only
> >>> handles 31khz & up sources, so I had not considered doing anything
> >>> but stuffing the coco's signals into the adjacent DB15, which
> >>> claims to work down to 15 khz, and which means one must pay
> >>> attention to the pinout of the 10 conductor cable from the coco as
> >>> to where it goes in the DB15.
> >> 
> >> Where in the manual does it say that?  The one I'm looking at claims
> >> that 15Khz. video can be applied to P3 (The large pins on the left),
> >> P11 (8-pin SIL) or P12 (HD15).

They are P3, P10, and P11 on my card, according to the silk screen.
 
> > Did you not get the xx20 version of that board?  Mine came with dual
> > db15 outs on the back edge.  And my booklet text says P3, P10, & P11
> > for the 15 khz input.
> 
> I have an older revision.  But, I think I misread your paragraph above. 
> I thought you were claiming that ONLY the DB15 accepted 15.75Khz.
> video. Ain't the English language great? 

Yup, one can confuse the issue regardless of which side one is arguing on. 
:)

> I agree that all three are
> intended to sync at that freq.  But, the big pins on P3 do not have
> anything brought out for H+V sync.
> 
> >> Since P3 appears to bring out only the
> >> composite sync input I never tried it.  I can tell you that H+V on
> >> P11 never worked for me.  I made the (perhaps erroneous) assumption
> >> that the H and V pins on the HD15 were connected to the same circuit
> >> nodes as H+V on P11.  But you know what they say about "assume" :-).
> > 
> > Yes, its been applied to me on numerous occasions.
> > 
> > A digital meter in ohms mode can tell that story.
> 
> I'll check after dinner this evening.
> 
> >> I've never been able to get mine to work with H+V sync on a 15Khz.
> >> signal. I wrote to their tech support and recall being told that it
> >> wasn't intended to work with H+V at that horz. freq - only composite
> >> sync.
> > 
> > That's a genuine class A bummer if by composite, they also mean fully
> > interlaced.
> 
> No nothing that draconian.  It simply needs a dumb two-chip sync
> combiner. I built one up on a proto-board and it worked just fine. 
> I'll send you the GIF of the schematic in private e-mail.
> 
And its now working?  Thanks!

> > Taking the coco's H & V, and combining them does not a
> > composite signal make.  In std Never Twice Same Color, the V Sync is
> > not a solid 3 line long signal, it is 'serrated' by returning to
> > black at 2x the h-rate, such that there is a 4.7 u-sec hole, which
> > returns to the sync output such that each serration end, is
> > co-incident with the falling edge of the H-sync for every other
> > serration.  That is why, years ago, you could adjust the vertical
> > hold to make the picture roll down, and the vertical sync bar you
> > could see had a square tail on the left end of the bar from the
> > middle to the right of the screen.  The one you couldn't see at the
> > left end would have been identical.  Its actually slightly more
> > complex than that because for 3 lines ahead of V-sync, the H sync
> > pulse was reduced to half its normal time to reduce any dc offsets
> > created by the apparent doubling of the repetition rate.  Ditto for 3
> > lines after the V pulse for exactly the same reason.  This is what
> > forms the arrow's 'tail' you could see.
> > 
> > Making composite by Nanding the two signals substitutes a solid bar 3
> > H lines long, which contains no H sync info, and causes the hooking
> > to the left or right at the top of the picture because the H sync is
> > momentarily lost.  That might well be the only thing we can do in
> > which case there is a bit of false advertising involved.
> 
> Wow.  Now I know who to ask about video particulars!

Chuckle.  That what you get when you are talking to someone who has made 
his living making tv work, from both ends, since about '48.  I am the now 
retired CE at WDTV, where I spent the last 18 years of my working life as 
the CE who could fix anything.  My phone still rings occasionally.

> > However I am still confused by the apparent differences in our
> > booklets, and now wonder which is correct.  Or are you miss reading
> > the PCB because the photos do not call the connectors out by their
> > P3, P10 or P11 designations?
> 
> No, I think we were saying the same thing.
> 
> Steve

I hope so now.
Cheers, gene
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