Re: Help wanted with B/W TV Mod
Hello Ian,
it seems that IC 201 has a built in sync separator. This kind of complicates want you want to do. There are two options:
1) find an input on IC201 that accepts a composite video signal, so you can inject your video signal before it is being processed inside IC201. I have not been able to find the data sheet for this chip so it is unclear whether it has a video input. From the looks of it it only processes the video IF RF signal.
2) Build a small circuit that strips the sync from your composite signal. This could be done with an LM1881 IC. You would have to feed the incoming signal to both the transistor Q801 and the input of the LM1881. From the LM1881 you would get a composite sync that you could feed into the connection point marked "F5". Make sure to disconnect pin13 of IC201 before feeding in the sync.
Please also note that you will need a clamping circuit for your video signal before feeding it into the base of Q801. If you just AC-couple the signal into Q801 via a capacitor without clamping, the average brightness of your images will change depending on the content of the video signal.
All things considered I would go for the UHF modulator approach. The loss in image quality will not be that significant if even visible and you can preserve the original state of your TV.
Just my $0.02
Cheers
Semir
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