Another issue is the gear may be old and failed. Test each VCR and DVR on it's own and maybe something's broke. Think up another way to wire it up.
I have an older tv that uses an RF modulator and a mini cable box. I connected the VCR and the DVR in the past but after taking it apart I cannot get both of them to work. I have the wall cable going into the mini box and then to the VCR and then to DVR and then to the RF modulator and then to the TV. Right now only the DVR works. Would adding a splitter between the cable box and the two units work better? Or would using two mini boxes work? The VCR and the DVR do not have tuners.

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