Author Topic: CPC Plus Video Signal  (Read 2712 times)

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Offline chinnyhill10

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CPC Plus Video Signal
« on: 23:34, 01 October 15 »
The new ChinnyVision 464 Plus has turned up kindly donated by Craigsbar and Fatbob. However having some issues with the video signal out of it for capture.


The setup I use for normal CPC capture isn't working. It seems the video signal from the Plus is higher than legal limits. I get a bright signal with sync issues.


Anyone know what the difference in the signal levels are between a CPC and a Plus? My 464 and both 6128's work with that setup but the Plus is causing issues. Higher voltages?


My other setup gives a black and white picture (although far brighter than the black and white picture from my original CPC's).


I'm stumped for capture until I figure this one out. The cable is from Retro Computer Shack as is my original CPC cable.


Any new signals in a Plus signal? From an initial look it appears that a signal (possibly sync?) may be higher than a standard CPC.


I would have included a frame grab but as usual the forum is complaining my image has "failed security checks". Sigh.


Cheers.
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Offline chinnyhill10

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Re: CPC Plus Video Signal
« Reply #1 on: 00:15, 02 October 15 »
Think I might have found the problem....


I think the menu system on the CPC4 card is in some odd screen mode/refresh rate that is sending the capture system mad. Similar to how Prehistorik 2 did. If you use a standard Burnin' Rubber cart or turn the capture kit on after you have exited the menu system, everything is fine. But if you activate the menu system it upsets the capture kit and it refuses to work until everything, CPC included, is reset.





That is a real CPC Plus capture direct from RGB. And I believe that might just be a first!


My office is now a mess of cables and I'm feeling quite stressed!  :'(
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Offline chinnyhill10

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Re: CPC Plus Video Signal
« Reply #2 on: 00:22, 02 October 15 »
Hmmm, no. Still appears to be erratic. Some stuff works fine but if you get large areas of colour on the screen it goes bad again. Has to be the signal levels. Overscan trips it up and if you look at that Burnin' Rubber grab the geometry isn't quite right.


Need to tame the signal levels perhaps? Cable appears to have resisters on the RGB pins. Higher values or resisters on other pins as well?
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Offline VincentGR

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Re: CPC Plus Video Signal
« Reply #3 on: 00:52, 02 October 15 »

Offline chinnyhill10

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Re: CPC Plus Video Signal
« Reply #4 on: 01:37, 02 October 15 »
Check this:

Connector:Monitor - CPCWiki


Has the pinouts but no details on voltages etc. Pretty convinced its a signal level issue. Need to take the cable apart and have a look at the weekend.
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Offline CraigsBar

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Re: CPC Plus Video Signal
« Reply #5 on: 01:47, 02 October 15 »

Has the pinouts but no details on voltages etc. Pretty convinced its a signal level issue. Need to take the cable apart and have a look at the weekend.
I'll have a look at my plus over the weekend and see what capture on the intensity pro in my Mac is like... Assuming i can find a way to cable it.
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Offline chinnyhill10

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Re: CPC Plus Video Signal
« Reply #6 on: 02:00, 02 October 15 »
I'll have a look at my plus over the weekend and see what capture on the intensity pro in my Mac is like... Assuming i can find a way to cable it.


I was happily playing Burnin' Rubber and the TV lost sync during one of the colour sky changes. So everything is pointing to signal levels being high. I'll check it with a multimeter at the weekend. If its way above spec (as I suspect it is) I should be able to fix it.
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Offline VincentGR

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Re: CPC Plus Video Signal
« Reply #7 on: 10:43, 02 October 15 »

I was happily playing Burnin' Rubber and the TV lost sync during one of the colour sky changes. So everything is pointing to signal levels being high. I'll check it with a multimeter at the weekend. If its way above spec (as I suspect it is) I should be able to fix it.

You do that, I don't have a plus machine to check it  >:(
And after that, maybe with some resistors you'll do the job.

Offline gerald

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Re: CPC Plus Video Signal
« Reply #8 on: 14:55, 02 October 15 »

I was happily playing Burnin' Rubber and the TV lost sync during one of the colour sky changes. So everything is pointing to signal levels being high. I'll check it with a multimeter at the weekend. If its way above spec (as I suspect it is) I should be able to fix it.
I've made some measurement on a 6128 and a 6128 plus, both connected to the same screen (75Ohm input) with home made cables (Alternate RGB wiring)
- RGB signal are a bit stronger on 6128 than on Plus (900mv / 850mv)
- Sync (used for RGB commutation) is identical (1V)
- Composite signals are different :
  The 6128 has a 750mVpp amplitude with 300mv sync pulse. The sync pulse amplitude is stable, whatever is on the screen.
  The 6128 plus has a 920mVpp  amplitude with a 200mv sync pulse. However the overall amplitude is not stable and you may end with a lower sync pulse. It is also sensible to screen content.

I do not know which wiring is used in you cable, but you may try to check using the SYNC instead of the composite for sync signal.
Note also that the composite signal amplitude can be tuned on the Plus.


Offline chinnyhill10

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Re: CPC Plus Video Signal
« Reply #9 on: 00:19, 04 October 15 »
I've made some measurement on a 6128 and a 6128 plus, both connected to the same screen (75Ohm input) with home made cables (Alternate RGB wiring)
- RGB signal are a bit stronger on 6128 than on Plus (900mv / 850mv)
- Sync (used for RGB commutation) is identical (1V)
- Composite signals are different :
  The 6128 has a 750mVpp amplitude with 300mv sync pulse. The sync pulse amplitude is stable, whatever is on the screen.
  The 6128 plus has a 920mVpp  amplitude with a 200mv sync pulse. However the overall amplitude is not stable and you may end with a lower sync pulse. It is also sensible to screen content.

I do not know which wiring is used in you cable, but you may try to check using the SYNC instead of the composite for sync signal.
Note also that the composite signal amplitude can be tuned on the Plus.


Thanks for the info. I spent the afternoon (as anyone who follows me on Twitter will know) playing around with the lead (as purchased from Retro Computer shack).


I nearly had something stable by taking the RGB resisters to 220 Ohms and putting a 50Ohm resister on sync. But it was never quite right. Picture always slightly jittery on peak whites if you looked at the edge of the text.


So I tried a different tack. Put the cable back to how it was (100 Ohm on RGB) and removed the RGB select cable. I then put a 1.5v battery on the RGB select.


All problems gone. No more occasional mis-sync on the TV and capture picture now totally stable even on a full white screen and overscan (which caused problems before).


So here's the theory. The Plus is varying the voltage on the RGB select pin depending on what is on screen. If there is lots of peak white the voltage drops causing problems.


Only a theory. All I know is that I spent 5 hours messing around and can now capture. The current setup looks messy however:





No idea how long the battery will last. I'll buy a proper holder and do it properly. I popped one battery soldering the wires on!  :laugh:


Still now have a totally stable picture which gives images like this (no tearing on the logo unlike the image at the top of the screen):










I think we may be in business!  :D



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Offline VincentGR

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Re: CPC Plus Video Signal
« Reply #10 on: 00:27, 04 October 15 »
Great!  ;D

Offline chinnyhill10

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Re: CPC Plus Video Signal
« Reply #11 on: 02:30, 05 October 15 »
Video is unlisted so it doesn't appear on the channel but here's a little demo. What happens when you don't pass the start line on Burnin' Rubber (yes, we've all known for 25 years but its still nice to hear that entire tune)


[youtube]http://www.youtube.com/watch?v=YLSAmU_6Qoo[/youtube]


Very nice clean capture. Have ordered up the bits to do a "tidy" version of my battery mod. Still no idea how long the battery will last!
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Offline seanb

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Re: CPC Plus Video Signal
« Reply #12 on: 03:04, 05 October 15 »
Nice.
How exactly did you get the map to keep tracking like that?
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Offline chinnyhill10

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Re: CPC Plus Video Signal
« Reply #13 on: 13:28, 05 October 15 »
Nice.
How exactly did you get the map to keep tracking like that?


You just qualify and then don't pass the start/finish line. So you just sit at the start until the clock runs down.
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Offline remax

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Re: CPC Plus Video Signal
« Reply #14 on: 18:57, 05 October 15 »
How many times have i done it in my local supermarket  ;D