Mc6847 TRS-80 COCO2 to Componet

[chjmartin2]

So here is what I did... I cranked open my TRS-80 Coco-2... I tapped onto the Phi A, Phi B and Y lum... I used the case ground as the ground for all three signals... then I plugged those suckers into my component input on my LCD TV... guess what... I got goose... nada... zip zilch...

So what am I missing? I used pin 28, 10 and 11...

Should I have left the ground open? Not used a ground? The spec sheet for the MC6847 says it can drive a TV directly... I did tap the input of the MC1372 because the pins on the MC6847 were too hard to get to... I did manage to get the Y lum direct from the MC6847 pin 28...

Who's the expert who can help me out? I must have a more clean TRS-80 COCO SIGNAL!!!!!

[oompa loompa]

the mc6847 signals cannot directly drive your tv. you'll have to build the amplifier that's on my page somewhere . it is only for luminance, so you'll only get a black+white picture , but it's a start. i dunno about the R-Y and B-Y signals though - i'll have to check the datasheet and tweek the amp resistor values to get the correct color . no time for me to do this though, so you're on your own on this one to get color video. using just the luminance output, you should be able to plug it into a composite video input on your tv too.

there is also a way to get composite video out directly from the mc1372, without having to demodulate the signal at the tv

haha, i think the mc6847 only had like 8 different colors it could generate, so you'll get like very little performace boost

[chjmartin2a]

Ok... so I built the Y-signal circuit... works great... I'd really like to be able to use an op-amp instead of a two transistor circuit... seems to me it would be cleaner... what would be the R1/R2 values - that is, what is the gain on your circuit? (I'm just not smart enough to figure it out..)