Problem DVD/VCR combos

I have recently bought two DVD/VCR combos. One was the Samsung DVD-VR357, and the one I bought today is the Toshiba D-VR610. They both have exhibited the same problem. When a DVD or VCR is playing, the t.v. picture flashes on and off in about one second flashes. They also did this when hooked up to my computer. Is there anything that I can do to fix it??