2600 Composite mod

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rubber_jonnie
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Re: 2600 Composite mod

Post by rubber_jonnie »

PhilC wrote: Sat May 18, 2019 2:13 pm Too many projects, too little time.
I hear ya, same problem here :(

Lawns need mowing, diswashers repairing, taps fitting, have to do Karate as my next grading is potentially at the end of July, but I have to pass the assesment in June first, the list is endless with not enough time or energy for everything.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: 2600 Composite mod

Post by exxos »

New output buffer chips finally arrived, but there is a slight problem :roll:

boo.jpg
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Re: 2600 Composite mod

Post by stephen_usher »

Wrong package type?
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
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Re: 2600 Composite mod

Post by PhilC »

Mount it upside down or on its side for testing at least? was that where the cap was supposed to go?
If it ain't broke, test it to Destruction.
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Re: 2600 Composite mod

Post by exxos »

The capacitor is on the bottom of the board, it is the pads which are the problem, as the bottom of the IC as a metal pad, so it would actually short out VCC and GND on the cap vias.

So I did this..

IMG_4210.JPG
IMG_4210.JPG (100.83 KiB) Viewed 5721 times

I get some strange black lines shooting across the screen at the moment. This chip is supposed to have automatic black level, it does have a adjustment, but it does not seem to do anything, and the black still does not look totally black either... Some more experimenting needed...

IMG_4211.JPG
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Re: 2600 Composite mod

Post by exxos »

Right, so its the AGC causing these issues kinda...

I put a couple of presets on the board so I can adjust the brightness and black level, but I can see the AGC slowly moving the brightness up and down basically counteracting what I am doing... And that some points it adjusts so fast it causes of raster lines in the black background...

So I am going to disable the AGC, and try again...

Overall I think the image does actually look better going via this new chip.

IMG_4212.JPG
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IMG_4213.JPG
IMG_4213.JPG (289.81 KiB) Viewed 5717 times
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Re: 2600 Composite mod

Post by PhilC »

It does look pretty good on the colours but black doesn't seem as dark as you had it before but it could just be the camera?
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Re: 2600 Composite mod

Post by exxos »

PhilC wrote: Thu May 23, 2019 7:49 pm It does look pretty good on the colours but black doesn't seem as dark as you had it before but it could just be the camera?
I think its the camera. I can still see black isn't totally black on my monitor, but I have the black level turned right down, and it actually starts getting brighter if turned down to much.. I think the AGC freaks out and gives it a voltage boost when black level goes to dim.

I tried without the AGC, and the brightness is all over the place, hard to get it stable.

I think it is as good as it is ever going to get, I mean it is only composite video after all, but I think a lot of these issues are relating to my crappy monitor more than anything.

Current mash up..
IMG_4215.JPG
IMG_4215.JPG (119.57 KiB) Viewed 5713 times

Overall I think I just need to add 2 presets onto the board, so people can experiment with the brightness and black level controls...
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Re: 2600 Composite mod

Post by exxos »

Pots added... SOIC package changed.. Data sheets says use 100nF and 1uF, I don't see the the point but I added in a second cap to each chip to try it out...

Now to wait for the next PCB order...

2.jpg
2.jpg (167.31 KiB) Viewed 5706 times

I may remove the middle chip and see if it works without it.. its only doing the video mixing, but likely just linking the 2 signals together will work.. will try and do that tomorrow...
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Re: 2600 Composite mod

Post by exxos »

I tried removing the middle chip, and just wire linking the inputs and outputs, but I could not get video at all, even adjusting the presets etc, but these chips are not particularly expensive anyway, so I will just leave it in..

IMG_4216.JPG
IMG_4216.JPG (101.57 KiB) Viewed 5692 times

I have tweaked the PCB again, basically adding in jumper pads to enable and disable the AGC, and to enable x2 brightness mode. However these adjustments have little effect when the AGC is enabled, as if you increase the brightness manually, AGC automatically decreases the brightness.

Overall I think just allowing the AGC enabled and just forgetting the manual settings is likely the way to go, but people will have to test this out on various monitors first.

1.jpg
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