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GiovanniG
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951 2HnD fault

Thu Oct 14, 2021 2:55 pm

Hi, I've a fault board, it doesn't react at boot, as I plug the power P5 lights on for 0,1sec, then P4 fully and P3 at 50%. Reset doesn't give any effect, there is a way to revive this board?
Thank you
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GiovanniG
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Re: 951 2HnD fault

Sat Oct 16, 2021 11:54 am

noone may suggest something here?
Thanks
 
r00t
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Re: 951 2HnD fault

Sat Oct 16, 2021 4:25 pm

If the LEDs are lit dimly, that usually means either power supply problems (ie. switching regulator, caps, ...) or CPU is dead/burned.
I would start with easiest thing first, replace all electrolytic caps - it's the most common problem with mikrotik HW.
Then measure voltages on all electrolytic caps to see if you have all required voltages (it helps if you have another working board you can compare with).
If any voltage rail is missing or different, switching regulator is dead and have to be replaced. For a quick test it's possible to run a board directly from lab powersupply, injecting all required voltages after switching regulators (ie on the cap pads), board should boot if it's OK and you will know it's just voltage regulator that needs replacing.
If all voltages are there and are correct, you can try to see if CPU is doing something - probe with a scope data lines going to flash to see if it's trying to access it.
If there is no activity, CPU is likely dead. You can try last resort hot air reflow, but it's rare these small chips would suffer this type of failure.
If CPU is trying to do something, it's possible flash is corrupted in some bad way... desoldering it and reading it may give a clue. It's possible to replace the chip, just make sure calibration block is copied from old one if possible (again helps to have multiple boards and chips so you know what you are looking at and what memory ranges change from device to device...)
 
GiovanniG
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Re: 951 2HnD fault

Thu Oct 21, 2021 2:10 pm

thanks for the great answer! I'll check the caps, hopefully there is the problem

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