S3 won't power up fully but turns on fan & drives spins

Remember that power supply is open frame and can bite very nastily, theoretically fatally.

Double check whatever it uses to connect the motherboard to the front panel where the lights and remote sensor are.

Powering up with it slightly disconnected on S2s is supposed to cause damage to motherboard components. (People learned this the hard way by accidentally jostling it when changing hard drives) Maybe the 3s are more forgiving, but it still has to be properly connected to operate properly.

Put your meter on DC Volts, 20, 25, or 50 Volt scale.

If you can find where the drive's power cable attaches to the power supply, and can get the probe tips to metal without touching other metal (maybe wrap electrical tape right up to the point where the probe sharpens to a point), the black is ground, the red should read right around +5, the yellow right around +12, and the orange, if used, right around +3.3 Volts.

If those aren't low (or, rarely, too high), then the power supply is probably working right and not being overloaded.

Of course if there was an "open" somewhere in the power lines to or on the motherboard, the power supply wouldn't be overloaded, but the Tivo wouldn't work.

If those readings are low, try booting with the drive disconnected, both power and data. If you seem to get some response from the motherboard, try running the hard drive from a computer power supply and let the TiVo just worry about the motherboard.

 

And if your power supply is marginal, the harddrive could suck up so much of its optput that there's not enough left for the motherboard.

After about half a century of being involved with electronics I have learned a thing or two about troubleshooting.

 

Is there some sort of fairly stiff ribbon cable connecting the power supply and the motherboard?

With the power cord unplugged from the wall socket and from the back of the TiVo (suspenders and belt) inspect that cable.

At least one end should, rather than being soldered, be slid into a socket of some sort. Ease it out (you may need to slide or flip a latching mechanism first) and inspect the individual bare metal connectors at the end of the cable. If all is well, re-insert squarely and fully, re-latching if necessary.

Do the same with the other end unless it's soldered, in which case use a bright flashlight and check that none of the wires are broken loose.


Then find the cable running between the motherboard and the front panel lights and IR (infrared) sensor. Inspect carefully both ends, but do not detach either if not absolutely necessary.

Apparently one end or the other of this cable can sometimes get slightly dislodged when changing out drives, and powering back up in that situation fries some transistors on the motherboard or the light board. Search this website for more info if you fear this is the case.

If you think you have both cables properly attached at both ends, power up with no drive attached and see what you get on the screen and the front panel.

Report back.