[Coco] CoCo 3 to RBG...

[Tim Fadden]

On 7/20/2011 2:37 PM, Steven Hirsch wrote:
> 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).
>>
>> 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?  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.
>
>> 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!
>
>> 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 also received one of these boards. (yesterday) Please share the two 
chip combiner circuit with me also.  I'm pretty sure I could build it, 
but not bright enough to design it!  :-)

Thanks

Tim Fadden