Our Series3 HD TiVo recently stopped working. The initial symptom was that the video gradually deteriorated as faint wavy lines appeared and moved up and down and back and forth across the screen. This lasted for a couple of months and I just didn't take the time to try to diagnose what was causing it. The effect was similar to what you would see if there was electrical interference affecting the coaxial cable but without static, only an ever-changing pattern of wavy lines that shifted their dance across the screen and disappeared and then reappeared.

But a couple of weeks ago the unit suddenly stopped displaying programming and started rebooting. It would display the Welcome screen for a few minutes, then the screen would go black for some seconds and then go back to the Welcome screen and this would continue until I pulled the power cord.

Thinking the problem was caused by corrupted data on the aging hard drive, I purchased a Western Digital WD10EVDS and copied the old hard drive using WinMFS and installed the new drive in the unit. When I started it up, it still would not progress past the Welcome screen and after some minutes would reboot. So, thinking perhaps the original hard drive had passed along corrupted settings to the new WD hard drive, I used the hard drive from a second, working TiVo S3 HD to try to initialize the new hard drive but it still would only boot to the Welcome screen and then loop back to the Welcome screen again and again. During this process, I tried a full copy of the original, failing hard drive. Then I tried a truncated copy of the original hard drive. Then I tried a truncated copy of the hard drive from a different TiVo S3 HD. In each case, the unit would start to boot to the Welcome screen and then restart.
At this point I tried WinMFS's bootpage fix with option 1. This didn't yield any better results. I then tried bootpage fix option 2 with similar results.
Then I read online that some of the WD green hard drives were being distributed with the intellipark feature so I created a boot CD with wdidle3.exe on it and ran wdidle3 /D to change the park setting to 62 minutes. This still didn't stop the endless reboot loop.
I then pulled both of the multi-stream cable cards and powered up. This time the unit progressed through the entire boot process until it got to the point where it realized there were no cable cards installed. It notified me that it was expecting two cards and instructed me to install the cards.
I followed the instructions on the screen which said to install the cable cards with the bottom card to be inserted first, but as soon as I installed the first cable card, the unit rebooted and entered the familiar boot sequence loop.

I tried booting the unit with only one cable card installed in the first position and that resulted in the endless reboot loop. I tried booting with only the second cable card installed and it entered the endless reboot loop. I tried swapping the cards and it entered the endless reboot loop. In short, I tried several different variations involving the cable cards and the only persistent observation was that the unit would not progress past the Welcome screen with the cards installed and, if I booted without the cards installed, it would immediately reboot as soon as either of the cable cards was installed.

With the combination of the faint wavy lines that dance across the screen and the reboot loop that only occurs when the cable cards are installed in the unit, I concluded that the power supply may be failing and has become too weak to provide adequate, stable voltage to the unit while the cable cards are installed.

I have ordered a new power supply to see if that will fix the problem.
Does anyone have any additional thoughts about this? Any other trouble shooting suggestions? At this point I am just trying to apply logical tests to see if I can get the unit to work but I do not have any formal education in electronics and I do not have specialized testing equipment to tell me if any of the motherboard components might be causing the problem. The power supply replacement seems like an easy and prudent measure to take based on the symptoms I'm experiencing but I wonder if someone with more experience sees something that would be worth investigating that I haven't tried yet.

Any suggestions are welcome. Thank you.