Looks like my original Series 3 Tivo power supply is bad. Is it possible to use a power supply from the Tivo HD (TCD652160) in the series 3 Tivo (TCD648250) to confirm this assumption?
The 648 supply has an extra 7.5V section not used in the 652/658 supplies.
Otherwise the pin-out to the motherboard is the same.
So using a 652/658 supply in a 648 won't blow anything up or start a fire but I can't promise that for the other way around.
However, I tried a 652 supply in a 648 a while back, expecting it to work except for the OLED display and it did not, so it might not be as simple as "the 7.5V section is for the OLED display and only that".
The better way to test is with a Voltmeter set on the 20 or 25V DC scale.
Clip the black (negative) lead to the metal chassis (the case) on the side away from the power supply, or jam the tip in one of the holes on that side, and use the positive (red) lead to backprobe the plug that goes in the socket on the motherboard.
Yellow=12VDC, red=5V, orange=3.3V and gray=7.5V.
You won't get exactly those numbers, maybe 11.8 or 12.2 or 4.9 or 5.1, although generally the 3.3 will be almost exact.
But if it's more like 11.1 or 4.2, then that probably indicates failure.
Also, it you get very much variation in readings depending on whether the hard drive is connected or not, that indicates an inability for the supply to "voltage regulate", which is also a sign of failure.
It's a 648 supply. If the caps haven't failed yet, it's just a matter of time. Replace them and be done with it. Might as well do the 652 supply while you're at it as well.