[Coco] [SPAM] Re: Cross Post from the Facebook Page about the RGB2VGA Board

[Steve Batson]

John,

Have you changed the resistors yet, or are you using the resistors recommended for the design? I was seeing jitter, where the entire screen would jerk and occasional waves going through it mostly noticeable on the edges. Also, it didn't seem consistent, sometimes it was worse than others. Based on what Roger had found, it sounded like there were a number of issues being caused by the original resistor values. Voltage Levels were not what they should be. Also there was issues with the HSYNC and VSYNC again caused by original resistor values. Luis and posted on the FB page a response to one of my questions that some CoCo's are noisier than others and this may very well be true, but I'd guess symptoms could be worse on some systems then others which could be the combination of the CoCo and Monitor. From discussions with Roger about this and how he fixed it, I'm going to go out on a limb here and suggest that with his suggested resistor values, the video will most likely be crisp, clean and jitter free on most any CoCo and VGA monitor unless they have problems of their own.

It was a bit of a pain in the butt pulling a bunch of resistors out and replacing them with Rogers suggested values, but I'd highly recommend it if you haven't done so already. It was totally worth it! If you have already replaced the resistors with the new values and are still having issues, I'd suggest the following:

1) Inspect your board and make sure you have no possible shorts. Clean it real good with alcohol or other good electronic board cleaner and thoroughly dry.
2) Check all the cables including power going to the board and make sure all is well
3) Make sure the ribbon cable isn't right next to a transformer including the CoCo power power supply (thought I am not having issues even if set the board right on top of the CoCo above the transformer). This probably is NOT an issue.
4) Remove wire I mentioned that was a ground fix.

Anyway, let me know if you have changed the resistors yet or not. I'm very curious to see where you are at.


On Jul 10, 2015, at 7:18 PM, John B <trymyz at gmail.com> wrote:

> Steve,
> 
> I tested the board out.  The display comes out fine, colors display
> properly, etc.  However, the edge of any line looks slightly wavy.  Hardly
> noticeable.  This is more evident with graphics opposed to text.  Of course
> I played with the trim pot, but that only helped so much.  Is this what you
> experienced before u swapped the resistors?
> 
> On Fri, Jul 10, 2015 at 11:36 AM, Steve Batson <steve at batsonphotography.com>
> wrote:
> 
>> 
>> 
>> 
>> No problem, Roger deserves the credit all this work. I just duplicated
>> what he did and putting info here hoping it's helpful.
>> 
>> 
>> 
>> I had no stock of resistors and trying to find just a few either wasn't
>> economical or easy. Needless to say, I've got a pretty good stock now!
>> :D
>> 
>>> Thank you very much Steve. I should be able to
>> test it out today. I will
>> 
>>> report back either way. I might put my DigiKey order in anyway. You
>> can
>> 
>>> never have too many resistors :)
>> 
>>> 
>> 
>>> On Fri, Jul 10, 2015 at 9:07 AM, Steve Batson
>> 
>>> <steve at batsonphotography.com>
>> 
>>> wrote:
>> 
>>> 
>> 
>>>> John,
>> 
>>>> 
>> 
>>>> No, the resistor from R7 to Pos 8 on the GPIO1 connector is what
>> was
>> 
>>>> referred to as Rx, that resistor should be 1.8K. The drawing on
>> Luis'
>> 
>>>> site
>> 
>>>> shows a jumper wire to fix a ground issue. If that jumper is in
>> place
>> 
>>>> after
>> 
>>>> all the resistors in place, you will most likely have Jitter.
>> There
>> 
>>>> should
>> 
>>>> be no Jumper wires installed. The jumper Luis refers to is
>> between R21
>> 
>>>> and
>> 
>>>> R18. I'd only install that if Jitter is present with all the
>> resistor
>> 
>>>> changes. If necessary, try it both ways, but on Roger and my
>> board it
>> 
>>>> wasn't necessary. All of these changes were Roger's findings. I
>> only
>> 
>>>> duplicated his setup and it's awesome!
>> 
>>>> 
>> 
>>>> 
>> 
>>>> 
>> 
>>>> On Jul 9, 2015, at 10:22 PM, John B <trymyz at gmail.com>
>> wrote:
>> 
>>>> 
>> 
>>>>> I will be testing it tomorrow. Thank you for the new
>> values.
>> 
>>>> Hopefully
>> 
>>>>> everything will work as intended. You refer to the
>> additional wires
>> 
>>>> not
>> 
>>>>> being needed. Is this the resistor from R7 to Position 8 on
>> GPIO1 and
>> 
>>>> the
>> 
>>>>> wire between R18 and R21?
>> 
>>>>> 
>> 
>>>>> On Fri, Jul 10, 2015 at 12:56 AM, Steve Batson <
>> 
>>>> steve at batsonphotography.com>
>> 
>>>>> wrote:
>> 
>>>>> 
>> 
>>>>>> John,
>> 
>>>>>> 
>> 
>>>>>> Yes, this is Luis' RGB2VGA board used with the DENano
>> FPGA.
>> 
>>>>>> 
>> 
>>>>>> Since you have just finished it, I'd test it out first
>> to see if you
>> 
>>>> see
>> 
>>>>>> any jitter or other problems. However Roger did a lot
>> of
>> 
>>>> investigation
>> 
>>>> and
>> 
>>>>>> found these values produce voltages in line with the VGA
>> Standard and
>> 
>>>> to
>> 
>>>>>> help the board properly sync from the CoCo output. I
>> don't have all
>> 
>>>> the
>> 
>>>>>> technical details, I just know it worked for Roger and
>> works for me.
>> 
>>>>>> 
>> 
>>>>>> These are what Roger came up with and I simply
>> duplicated what he
>> 
>>>> found.
>> 
>>>>>> Also, the Variable resistor, he recommended a 10K Multi
>> Turn for
>> 
>>>> finer
>> 
>>>>>> control when tuning for the best appearance. Another
>> thing to know is
>> 
>>>> that
>> 
>>>>>> there are some additional wires recommended but they
>> were not needed
>> 
>>>> on
>> 
>>>>>> Roger's or my case and jitter did not go away until
>> removed.
>> 
>>>>>> 
>> 
>>>>>> Top Left
>> 
>>>>>> 
>> 
>>>>>> 82 Ohms - Grey-Red-Black-Gold-Brown
>> 
>>>>>> R22
>> 
>>>>>> R23
>> 
>>>>>> R25
>> 
>>>>>> 
>> 
>>>>>> * * * Bottom Left
>> 
>>>>>> 
>> 
>>>>>> 1.2K Brown-Red-Black-Brown-Brown
>> 
>>>>>> R18
>> 
>>>>>> R19
>> 
>>>>>> R20
>> 
>>>>>> R21
>> 
>>>>>> 
>> 
>>>>>> * * * Top Right 10
>> 
>>>>>> 
>> 
>>>>>> R9 47
>> 
>>>>>> R10 47
>> 
>>>>>> 
>> 
>>>>>> 390 ohms
>> 
>>>>>> R1
>> 
>>>>>> R4
>> 
>>>>>> R7
>> 
>>>>>> 
>> 
>>>>>> 820 ohms
>> 
>>>>>> R2
>> 
>>>>>> R5
>> 
>>>>>> R8
>> 
>>>>>> 
>> 
>>>>>> 1.8K ohms
>> 
>>>>>> R3
>> 
>>>>>> R6
>> 
>>>>>> Rx (this is the resistor soldered to R7 and the GPIO1
>> Connector)
>> 
>>>>>> 
>> 
>>>>>> * * * Bottom Right
>> 
>>>>>> 
>> 
>>>>>> 2K Red-Black-Red-Gold
>> 
>>>>>> R17
>> 
>>>>>> R14
>> 
>>>>>> R12
>> 
>>>>>> R11
>> 
>>>>>> 
>> 
>>>>>> 1K Brown-Black-black-Brown-Brown
>> 
>>>>>> R15
>> 
>>>>>> R16
>> 
>>>>>> 
>> 
>>>>>> 
>> 
>>>>>> 
>> 
>>>>>> 
>> 
>>>>>> On Jul 9, 2015, at 9:31 PM, John B
>> <trymyz at gmail.com> wrote:
>> 
>>>>>> 
>> 
>>>>>>> Steve,
>> 
>>>>>>> 
>> 
>>>>>>> Are you referring to Luis' RGB2VGA board? The reason
>> I ask is I
>> 
>>>>>> literally
>> 
>>>>>>> (15 min ago) just finished assmebling my board. I
>> used the
>> 
>>>> resistors
>> 
>>>> he
>> 
>>>>>>> outlined on his page under the
>> "Modifications" section.
>> 
>>>>>>> https://sites.google.com/site/tandycocoloco/rgb2vga
>> Are those the
>> 
>>>>>>> resistors that produced the video jitter? If so, can
>> you give us
>> 
>>>> the
>> 
>>>> new
>> 
>>>>>>> values that fixed the issue?
>> 
>>>>>>> 
>> 
>>>>>>> Thanks,
>> 
>>>>>>> 
>> 
>>>>>>> John
>> 
>>>>>>> 
>> 
>>>>>>> On Thu, Jul 9, 2015 at 11:45 PM, Steve Batson
>> <
>> 
>>>>>> steve at batsonphotography.com>
>> 
>>>>>>> wrote:
>> 
>>>>>>> 
>> 
>>>>>>>> I figured I'd post the following here too. Some
>> discussion occurred
>> 
>>>> on
>> 
>>>>>> the
>> 
>>>>>>>> FB page, but a lot of discussion was done
>> between Roger and Myself
>> 
>>>> in
>> 
>>>>>> email
>> 
>>>>>>>> as Roger made several discoveries that
>> stabilized some very
>> 
>>>> annoying
>> 
>>>>>> jitter
>> 
>>>>>>>> problems with video.
>> 
>>>>>>>> 
>> 
>>>>>>>> RGB2VGA Stabilized!
>> 
>>>>>>>> First thanks to Felipe for a very cool Solution
>> to bring the CoCo3
>> 
>>>> video
>> 
>>>>>>>> to Modern VGA Monitors. Originally, I missed a
>> few resistors that I
>> 
>>>>>> somehow
>> 
>>>>>>>> thought were optional and Felipe straightened me
>> out on those.
>> 
>>>>>>>> Then I was getting Jitter just like Roger was
>> experiencing. I had
>> 
>>>>>> several
>> 
>>>>>>>> email discussions with Roger as he was doing
>> some research and
>> 
>>>>>>>> experimenting based on what he found about the
>> VGA standards and
>> 
>>>> found
>> 
>>>>>> that
>> 
>>>>>>>> changing some resistor values stabilized the
>> output from his board.
>> 
>>>> I
>> 
>>>>>> have
>> 
>>>>>>>> pretty much duplicated Roger's resistor values
>> on my board with the
>> 
>>>>>>>> exception of 4 that I'm waiting to come in, but
>> mine is crisp and
>> 
>>>>>> jitter is
>> 
>>>>>>>> gone. I will most likely change those 4
>> resistors when the parts
>> 
>>>> come
>> 
>>>> in
>> 
>>>>>>>> unless it doesn't make sense.
>> 
>>>>>>>> Anyway, Finally fantastic output on my VGA
>> monitor. Very Cool!!!
>> 
>>>>>>>> Very Big thanks to Roger!!!
>> 
>>>>>>>> 
>> 
>>>>>>>> --
>> 
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>> 
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>> 
>>>>>>>> 
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>> 
>>>>>>>> 
>> 
>>>>>>> 
>> 
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>> 
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>>>>>> 
>> 
>>>>>> 
>> 
>>>>>> 
>> 
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>> 
>>>>> 
>> 
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>>> 
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>> 
>> 
>> 
>> 
>> --
>> 
>> Steve Batson
>> 
>> Website: http://www.batsonphotography.com
>> 
>> Facebook:
>> https://www.facebook.com/pages/Batson-Photography/313748145356
>> 
>> Gallery: http://gallery.batsonphotography.com
>> 
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