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VCR demodulator hack

 
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doomcuroe
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PostPosted: Thu Oct 11, 2007 6:56 pm    Post subject: VCR demodulator hack Reply with quote

Hi, I was just wondering if I want to use a VCR for the sole purpose of demodulating RF to the 3 RCA cables so I can connect cable to my reciever, does the VCR have to have power to do this?

I'd rather not have a whole VCR plugged in just to convert these signals and I dont want to spend hundreds of dollars for a commercial demodulator. Is there a way to remove the board that the inputs/outputs are attached to and create my own housing for a more compact device by simply supplying power to the board? I wonder how to identify which pins to solder the power source to and how much voltage the board requires? Its an old Electrohome VCR with stereo output. Thanks!
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Fri Oct 12, 2007 4:23 am    Post subject: Reply with quote

Question Not exactly sure what you are trying to accomplish? Can you rephrase and be more specific as to your application?

In general any RF modulator can be used separatley for modulating audiow/video and---yes it needs have a DC source, but why would you need it for a receiver?
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doomcuroe
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PostPosted: Fri Oct 12, 2007 4:44 pm    Post subject: vcr hack.. Reply with quote

Ok, my problem is this: I simply want to connect my cable (normal non-digital) to my home theatre system without having to go through a VCR. My reciever does not have a coax input.

So I figure that maybe I can make my own device using an old VCR to convert coax signal to the RCA type (demodulate) my reciever accepts.

I opened up the old VCR and found that the coax (cable) input and the RCA outputs are on the same circuit board and thought that maybe if I supply power (if needed) to this board alone it would function as a demodulator. Iwould make my own enclosure and the whole thing would be smaller than the original VCR.

I thought about it more and realized its probably not that simple. I bet the board has power when the VCR is plugged in and then some other kind of power once the VCR is turned on to get the demodulator part of the circuit working. I also bet that power is fed to the board at multiple points and maybe multiple voltages as well.

I cant find a circuit schematic and even if I did I only barely understand them, and unless I get this VCR reverse engineered- I'm in over my head. AM I right? THanks!

Dave
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Sat Oct 13, 2007 4:48 am    Post subject: Reply with quote

... in another words, you want to be able to hookup the audio from your cable to your stereo system by means of (left-right) RCA cables and want to use a demodulator instead of a whole VCR ---right?

While you have the right idea, it is NOT how it works;

Let's backtrack a bit;
The cable signal operates in various bands in the RF spectrum, thereby it needs to be first "Tuned-in" and then converted down in freq. BEFORE it can be demodulated to usable audio/video signal(s), meaning that you need to have:

1) Front-end Tuner & needed associated circuitry
2) Demodulator to change it into usable Audio/video signal. Both of which can be done by a TV or a VCR's (tuner section). So the box that you see inside the VCR is not a simple demodulator; rather a Tuner/demodulator/modulator all in one. But you still need to have some form of control circuitry---too much for an average person & simply not worth the hassle regardless.

Does your TV set have audio outputs? (most likely) Why not utilize them instead?
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doomcuroe
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PostPosted: Sat Oct 13, 2007 4:24 pm    Post subject: vcr hack... Reply with quote

THanks for your input. Yes my tv has audio out but I cant get any sound out of them... Above the audio out rca outputs in brackets it says variable/fix. I tried avarything I could to get it to work. No sound. Someone told me that I had to change the setup on the tv for audio out to be fixed, but I only have a cheap radio shack remote without a menu option. I guess I'm SOL, and have to buy a VCR....?
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