Yep going to do a new post about this gem. And making sure the red colours and discalaimers are added!
Doing the ground work on the SYSCON connection via serial uart mode document - asked mina to proof read as he has been giving me loads of useful info! - So thanks @mina
So back to the thermal monitors
As a hobby I fix the old PS3 fats, restore them then sell them or give them away depending on condition.
I've had plenty of ps3 boards to mess about with and break each bit to see what syscon says.
The two central thermal monitors for say the SEM-001 board CELL and RSX the ADT7461 are rare to break but a short by accident or whatever will kill them as on standby pin 1 is always live 3.3V on them.
I think they die more often now as people open their ps3 up and probably short them by mistake!
The fail safe i think was by design for sony, as the syscon cant communicate to those monitors then it just defaults to 100% mode on the fan - the pwm is directly connected to the syscon chip so always has control regardless.
I removed the thermal monitors to see what happened, and yes it booted but fan was 100%
The syscon console messages showing temp value errors confirms that if no communication it falls back to FF mode.
And finally, the fantbl is fascinating as it shows that sony did a rush job of setting a terrible default
0 CELL
fantbl get 0
fancon No:00
P0: TempD:0.0(0x0000) - TempU:76.0(0x4c00) duty:20%(0x33)
P1: TempD:56.0(0x3800) - TempU:77.0(0x4d00) duty:29%(0x4a)
P2: TempD:56.50(0x3880) - TempU:82.0(0x5200) duty:30%(0x4d)
P3: TempD:57.0(0x3900) - TempU:83.0(0x5300) duty:31%(0x50)
P4: TempD:57.50(0x3980) - TempU:84.0(0x5400) duty:32%(0x52)
P5: TempD:58.0(0x3a00) - TempU:85.0(0x5500) duty:34%(0x57)
P6: TempD:58.50(0x3a80) - TempU:86.0(0x5600) duty:36%(0x5c)
P7: TempD:59.0(0x3b00) - TempU:87.0(0x5700) duty:55%(0x8d)
P8: TempD:79.50(0x4f80) - TempU:88.0(0x5800) duty:65%(0xa6)
P9: TempD:80.0(0x5000) - TempU:91.0(0x5b00) duty:100%(0xff)
P10: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P11: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P12: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P13: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P14: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P15: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P16: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P17: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P18: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P19: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
1 RSX
fantbl get 1
fancon No:01
P0: TempD:0.0(0x0000) - TempU:84.0(0x5400) duty:20%(0x33)
P1: TempD:56.0(0x3800) - TempU:85.0(0x5500) duty:29%(0x4a)
P2: TempD:56.50(0x3880) - TempU:86.0(0x5600) duty:30%(0x4d)
P3: TempD:57.0(0x3900) - TempU:87.0(0x5700) duty:31%(0x50)
P4: TempD:57.50(0x3980) - TempU:88.0(0x5800) duty:32%(0x52)
P5: TempD:58.0(0x3a00) - TempU:89.0(0x5900) duty:34%(0x57)
P6: TempD:58.50(0x3a80) - TempU:90.0(0x5a00) duty:36%(0x5c)
P7: TempD:59.0(0x3b00) - TempU:91.0(0x5b00) duty:55%(0x8d)
P8: TempD:77.0(0x4d00) - TempU:92.0(0x5c00) duty:65%(0xa6)
P9: TempD:78.0(0x4e00) - TempU:95.0(0x5f00) duty:100%(0xff)
P10: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P11: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P12: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P13: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P14: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P15: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P16: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P17: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P18: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
P19: TempD:255.75(0xffff) - TempU:255.75(0xffff) duty:100%(0xff)
These are insane values, but even more worrying is that is not the same for all boards - Another SEM-001 board as different values as these fan tables are programmed via the eeprom, so dont change on sys updates - tried this out.
Nice you are going to share how to edit the fantbl

Better post it in the thread where we was talking about all this, there is not much info in the forum about how all this works so is better to cummulate it in the same thread
Or create a new thread dedicated to it... but remember to add huge warnings in eyebleeding red colors and bold
My logic when i was writing my previous posts of this thread (please reads all them, not sure if you missed some of what i was trying to explain) is the thermal monitors from PS3 slim looks very robust, also the only "input" they have is just a signal from the thermal sensor inside CELL/RSX, and that input is going to be very stable even in the worst conditions (lets say CELL or RSX dies by overheat... but the thermal signal sent by them is going to be still under normal values)... so that input is not able to damage the thermal monitors
I guess the only way that could be damaged is by a massive overheat.... but if we consider that are components related with thermal it would not surprise me if they can keep working normally over high temperatures like 90ºC or more... they should be ready for it
Anyway... this im saying applyes mostly to the thermal monitors used in PS3 slim onwards... but im not sure how looks or the specs of the thermal monitors used in the first PS3 models... maybe are a bit more weak and more prone to malfunction
Actually, you are the first person i see saying in a forum that eventually the thermal monitors of the PS3 fats can malfunction (the other day you wrote a post about it, not sure in which thread), thats pretty interesting, but believe me i been reading forums related with PS3 scene since years ago and never seen anyone mentioning it, this shows how infrequent is it
Back to how syscon works.... lets say the thermal monitor starts malfunctioning... it seems in that case syscon takes the value 0xFF for it, but we dont know why... maybe is just an unexpected consequence caused by how the communication protocol in between syscon and the thermal monitor works... or maybe the syscon is ready for it detects the problem and outputs the 0xFF just as an indication about it (like an error output, for repair purposes)