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

[Steve Batson]

Ed, the recommended resistors do not provide the proper voltage levels for the VGA circuit, that's what Roger found out after much painful research and experimenting. Neither of our boards were stable with the design recommended voltages. With Roger's recommendation, Both Roger's and mine are Rock Solid.

I have the 91% Isopropyl myself, a little dispenser and a small acid brush...works good, but I like our idea about soaking the board for a bit...that might not be a good idea for all components would it? Electrolytic caps, transformers, etc. Way back when, I used to use denatured alcohol with the acid brush and it worked awesome.


On Jul 10, 2015, at 8:05 PM, Zippster <zippster278 at gmail.com> wrote:

> I’m following this thread with interest, as I’m going to be finishing up theRGB2VGA boards that people had ordered from Kip
> to get that project successfully completed.
> 
> It is true that different monitors are more or less tolerant to certain differences in signals, that could explain
> some of what is being seen here.
> 
> Regarding cleaning boards, 91% isopropyl alcohol works wonderfully.  What I do is submerge the boards in the iso in a small
> tupperware type container, soak for 10 minutes or so, brush them with a toothbrush while in the bath, then rinse with fresh iso and air dry.
> Be sure to use the 91%, the lower concentrations have too much water in them.  It’s available at drug stores, walmart, etc.
> 
> - Ed
> 
> 
>> On Jul 10, 2015, at 9:39 PM, Steve Batson <steve at batsonphotography.com> wrote:
>> 
>> 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.
>> 
>> 
> 
> 
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