Originally Posted by FishTail74
1) What's the INTERNAL blue light (on the motherboard) mean ? (Current suspicion is it means "start-up prevented, due to low power", since upgraded HDD is 6.5 watts more, and power brick has only a 24 watt total rating)
I'll answer it but leave you with more questions.
There's actually 4 internal LED lights on a Base Roamio board.
Blue and Green are used during booting probably as checkpoint indicators. I'll elaborate.
Embedded developers code on a PC and upload to the board the build for testing. Many times, a bug you introduced will prevent it from booting all the way, so you put statements in the code at critical operations to indicate it's gotten past that hump. When there's a terminal, you can print a detailed progress, but without, when you just have the board you resort to these LED indicator lights, as a broad stroke.
That's a long way of me trying to say, the BLUE LIGHT is not an error message per se, everyone's Roamio does that. The trouble is it does not turn off, so it was the last OK message [ "I'm here" ] to make it out, before getting stuck or derailed.
From my memory, the stages during a normal boot are:
a) Blue external + Red external LED's then
b) Blue internal LED then
c) Green internal LED then
d) Green external + Yellow external flashing LED's
d) is what we call Kickstart entry, so the c->d transition is triggered by a startup script
The Roamio hardware boots really fast so it's hard to eye for certain what's doing when, without some contraption.
I'm going to guess from experience, the b->c transition is an instruction in the bootloader.
That might leave the a->b transition, an instruction (if it can be called that) in the verifier (for the bootloader). That's a guess, or more precisely a deduction on shaky information.
The off->a transition may be a hardwire for when chips reach ready.
The best way to find out for sure is someone who consistently gets a stuck blue light, would need a TTL serial cable monitoring for a descriptive error message being printed out.
If someone's box does this reliably and wants to volunteer, I'll write out the directions. Requires a USB computer near by. It also might not say anything. If it's too early, it might use a lower level communication channel.
Alternatively, the box is not 100%... if you contact Tivo Support and can have the details passed to Engineering (if it appears it's not in their error troubleshooting script) the developers should easily recognize it, but you might not get a better explanation than it needs to be replaced.
Why does the first stage have two LED's ? Is it two CPU cores, two chips?
Where is the bootloader stored that it could not pass verification sometimes?
When does the Red or Yellow LED get used? Unlocked bootloader? An Error condition?