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 Post subject: Laseractive RGB amp - advice?
PostPosted: Sun May 02, 2021 5:22 am 


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Joined: 30 Jul 2020
Posts: 27
Hello,

I've recently been wanting to mod my Laseractive for RGB output. This is the circuit I came up with after looking at the service manual:

https://cdn.discordapp.com/attachments/ ... nknown.png

The problem here is that I couldn't figure out what's the voltage range for R, G and B when tapping them from the jumper lines close to IC808 (the IC that overlays RGB with the LD's video signal). The color signals come straight through from the PAC and I couldn't find any service manual/diagram on the PCE/MD pacs themselves, so their voltage ranges are a big mystery. The only thing I know is that the signal IS 0.7v peak to peak on IC808's pins (since that's the operational range the IC describes on its datasheet), but as the jumper wires comes before a 330 ohm resistor and a 20uF eletrolytic, I'm not sure if I:

1. should plug R, G, B directly into THS7316
2. add 330 ohm resistors in between the jumper wires and THS7316
3. add a voltage divider of unknown value* between the jumper wires and THS7316.

*I've seen people saying that they used PC Engine RGB amps here, so I could just copy resistor values from another unrelated design for that console.

I'm also not sure about the role of eletrolytic capacitors on the THS7316's output, as I've seen from some designs for other consoles. I'm intending to plug a Neo Geo CD SCART cable into this and I'm sure there are some caps in the cable itself, so I'm not really sure if they need to be added.

Thanks in advance for any pointers.


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