Intellivision Has No Color

[Tempest]

I have an Intellivision Model I with a composite video mod hooked to a nice little Sony monitor and it worked just fine. The color took a second to kick in for some reason, but it always did. Now I've hooked it up to a different monitor (a JVC) and it's permanently in black and white. The color never kicks in. Any idea why this might be? Is the color pot possibly adjusted just a little too far out of range for the new monitor to detect somehow?

[nick3092]

Could be the colorburst crystal is way off, and was getting back into the proper range once warmed up.

 

Or the variable capacitor tied to the crystal is off. Do you have a frequency counter or digital oscilloscope that can calculate frequency for you? That would be the first thing I would check if you have the equipment.

 

Otherwise it could also be a bad IC too (STIC or the color IC) that would work once warmed up. But unlike the crystal, I don't know of a way of checking the IC without swapping mg in a known good one.

[Tempest]

It doesn't really have to warm up, on the other monitor it goes from B&W to color in about a second. I'll try and muck with that crystal tonight and see what happens.

[HunterZero]

+1 try adjusting the C2 variable capacitor and see what happens, and check capacitor C1.

[Tempest]

I assume that C2 is that little disk you turn to adjust the color?

[nick3092]

Yes. Ideally you would use a non metal adjuster (a metal screw driver will affect the capacitance) and a frequency counter.

 

Lacking that, you could try noting the original position and try some small adjustments in either direction. You can always put it back to the original position that way.

[Tempest]

Fixed it. It was the color adjust dial. A little turn and I'm back in color. With greenish yellow and ghosting.... but it's still better than RF.

 

 

Where's my S-Video mod?

[+-^CrossBow^-]

Fixed it. It was the color adjust dial. A little turn and I'm back in color. With greenish yellow and ghosting.... but it's still better than RF.

 

 

Where's my S-Video mod?

 

Interesting you mention this because in looking at the schemes, it does appear that luma and chroma exist. I'm sure they need other adjustments and can't just be snagged as is, but unless the schemes are lying...it would seem that the signals are present for this?

[mr_me]

Which schematic are you using. The ay-3-8915 outputs four signals, it's not clear what they are. It would be nice if one is luma and another colour. Here's an official schematic, some have additional markings.

 

http://spatula-city.org/~im14u2c/intv/tech/images/schematic.png

 

Edit:

And here's an explanation of the ay38915 output. It sounds like it's all composite.

http://atariage.com/forums/topic/139958-intellivision-video-upgrade/?p=1699156

 

A decent video upgrade should involve an ay38915 replacement or tapping into the five bit digital output of the stic chip providing dac as well as colour definitions for all 16 colours.

Edited August 4, 2018 by mr_me

[JohnPCAE]

Indeed, the AY-3-8915 directly outputs composite video. The resistor ladder just downstream of its outputs finalizes the D-A conversion.

[mr_me]

Is there anything that distinguishes the function of the four output signals coming from that chip?

Edited August 5, 2018 by mr_me