CV Composite/ S-video and two channel audio + BIOS mod

[omnedon]

Well, it's finally done. I've done the AV and BIOS mod for a spare ColecoVision. I used the Composite method from here: http://www.a1k0n.net/projects/coleco/, and the S-video from here http://www94.pair.com/jsoper/cv_svideo.html, except I altered it (switched) so the two mods could co-exist. I also went with two mono audio channels instead of one, so you can get two speaker audio, from standard AV cables, no splitter required.

Pics!!

The jacks.


Now, this was a spare CV. I'm going to now use it as my personal one. Now that I've done one, the next one I do will have cleaner and better jack placement. Not pictured is a small switch, also on the back, that allows the composite and S-video to exist in the same unit.

Composite screenie:



Notice how black the black is. How much more black could it be? ( :lol: Spinal Tap reference) With the composite signal, the colours seem truer than RF, and have less bleed. Visual noise (static sparkles) are GONE. Mr. Smashy was over last Wednesday, and wrapped Pepper II on the unfinished mod last week (composite only). Many CV games use a black background, and the absence of visual noise is the most striking, next to the more vivid colours.

S-Video Screenie:



Sharper yet. Bleed nearly eliminated, and the colours just seem to *pop* more brightly than the composite. Only one problem with the S-Video - it will not work with the Atari expansion pack. the audio and the composite work fantastic with the Atari expansion pack, but no S-video. There seems to be no easy way for me to pull a Luma signal from the Atari expansion, without wiring it to the CV permanently, or running some frankenstein style wiring on the exterior of the two units. Yuck. S-video for CV games only I guess. Pixels so sharp, they may cut you. :lol:

I think those screenshots are quite impressive looking, considering it's a 1 MP Digital camera pointed at my TV.

The audio is a big jump from the flat RF audio, with a much sharper and brighter sound, in two mono channels no less! The BIOS mod is the standard Deathskull BIOS mod from here:
http://users.erols.com/tiltonj/games/tech/ that allows a press of fire, to let you skip the very long COLECOVISION presents splash screen should you desire to.


If anyone wants to do this themselves, I'm always up to answer questions. John Soper was kind enough to clarify some things for my adaptation on his mod, and I'm happy to share what I've learned as well. I will be willing to do this mod for others, for $ or trades. I'm in Canada, which makes the exchange rate very favourable to Americans.

I will be doing another for Ebay, in an entire set.

OK. I'm done bragging. Time to play some Zaxxon and some Spy Hunter. 8)

[chadtower]

I was looking at these mods earlier... I don't have enough knowledge to follow the A/V amp board diagram. I'd love to do it but it will have to wait until I know more.

[FABombjoy]

Hey, I've heard the s-video has vertical lines. I take it you didn't experience this? If not, I'm doing this mod tonight.

[omnedon]

On solid colours, say the level select screen for example, they are indeed visible. They seem so minor to me, that not doing the mod because of it seems silly. Once you see the lines, you can see them in RF too, if you really look. Extremely faint. Small price to pay for the vastly improved clarity in video and sound, and if you have the Atari expansion, you can benefit with Atari games as well. The lines remind me of the difference in the Svid mod on a high serialled Neo AES, and a low serialled one. Those who haven't done a side by side can't see the difference.

Now, I used a single ground for all jacks, rather than running mutiple grounds from multiple points. That may have helped, but I really doubt it. The picture is stable. I do not really think I've improved on A1kon's or John Soper's work, but merely added a switch. I really wanted both in the mod.

EDIT

More pics! I've got mixed feelings about these RF shots. This is RF using a high quallity Co-Ax switch, all shielded cable, and an F-plug. This RF set up totally blows way what RF looks like with the switch many people commonly use instead. Nevertheless, you can still tell the difference, even with RF optimized like my set up is.

ALL pics, same TV, same camera, same ColecoVision, as the mod does not break RF functioning.

RF splash screen:


S-Video splash again for reference:


RF level select:


S-Video level select:


Note the faint vertical lines. I can see these same lines in RF, but they are harder to see.

And for the heck of it, RF Frogger:


And S-Video Frogger:


I'm hoping to give perspective with these pics. I just feel a bit awkward about my RF example, as my RF example is as good as RF gets, as opposed to what people commonly suffer with. The most abvious difference in these pics is the colour saturation. It does indeed *pop*.

[FABombjoy]

Well, I did the s-video mod this weekend, only problem is that I have a very weak luma signal. Weak enough that it takes a screen full of bright objects before a tv/monitor will even hold a steady picture. I've picked luma from the right side of L9 just as the instructions stated. Actually tried both sides, with and without 75ohm resistor. Anybody have any ideas? It's a Canadian model Colecovision, if that makes any difference.

Oh yeah, when I got to the composite stage, the composite signal looked just fine. Only the s-video version doesn't work quite right.

[omnedon]

I'm working on another for Ebay right now. A Canadian one as well.

I found it hard to get a good connection to the right side of L9 on this board, as there is virtually no bare metal exposed on the post. I had to work it a bit.

Maybe you could try tapping L9 from the underside of the board?

[FABombjoy]

Maybe you could try tapping L9 from the underside of the board?

Yeah, that's actually what I did. I don't think it's a connection problem tho; if I tug on the cable/push on the solder joint the picture remains unchanged.

[omnedon]

Maybe your electronic componet at L9 is faulty? It's a monolithic ceramic cap, right? If it isn't a cap, what is it?

You could try a same rated replacement component at L9?

I'm getting an identical signal from L9 on this second CV, as I did from the first one.

I'd try to swap that component.

[FABombjoy]

L9 is (according to the schematics that I've found) a 43mH coil...

I tried reverting the circuit back to standard composite and that doesn't work correctly either. Same issue - weak luma. Oh well, time to keep prodding.

[FABombjoy]

Ok, going back to square 1: Removed the circuits entirely & defaulted to RF.

I'm getting a screen that rolls, sometimes slowly with intermittant colors and a wavy image, sometimes quickly with no colors.

The Colecovision FAQ says that it could be a problem with the power switch. I read a solid 12 & 5 volts on the switched contacts.

I'm gonna let it cool down for awhile and see if it isn't heat related.

[FABombjoy]

Well, problem identified:

After looking at pics of other colecovision guts, I've come to the conclusion that someone removed the heat sink from the TMS9928a video chip at some point. I can only imagine how long it's been running without proper heat dissapation.

Also, after reading the datasheet for that chip, it should be able to drive an external video source without any need for a buffer/amp. So, I desoldered L9, pulled the Y line to VSS via 330ohm resistor (as spec'ed in datasheet), & hooked it up to my monitor. Rolling picture. Turned over my can of compressed air & froze the 9928... Picture stabilized. Held soldering iron over chip... a few seconds later, picture turns blank.

Anybody got bad CV with a stable picture that I can harvest that chip from? I examined a spare 99/4a that I have, but it uses the 9918 which only outputs composite.

[omnedon]

I have some parts CV boards, that have a 'likely' working chip.